Engine driven gear fuel pumps type "C" (Power Plant Section report)

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Auburn University Libraries
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File D 52.46/39
Vol. V
ION CIRCULAR
CAVIATION )
PUBLISHED BY THE CHIEF OF THE AIR SERVICE, WASHINGTON, D. C.
May 1, 1924 No. 464
ENGINE DRIVEN GEAR FUEL PUMPS
TYPE '·'C"
( POWER PLANT SECTION REPORT )
Prepared by Mr. H. C. Osborne
Engineering Division, Air Service
McCook Field, Dayton, Ohio
January 10, 1924
WASHINGTON
GOVERNMENT PRINTING OFFICE
1924
---·
Ralph Brow:1 Draughon
US RARY
MAY 16 2013
Non·Depoitory
Auburn University
CERTIFICATE: By direction of the Secretary of War the matter contained herein is published as adminis­trative
information and is req uired for the proper transaction of the public business.
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OUTLINE
( NECESSITY FOR AN ENGINE-DRIVEN PUMP --- - -------- ---- ------"------- - - - - --- - ------ - - - - --- -
1. Gravity _ __ ________________ ____ · _ ____ __ ______ ___________________________ ________ ___ __ 2. Vacuum and g~a vi ty ____ _______ ____ ____________________________ ____________ ________ ___ _
3. Air pressure ___________ __ ____ _______ ________ _ ~ ____ ____________ ____________ ___ ___ __ ____ _
4. Fu~ pumP -- -- -- -- ------------------~--------- - ----- - - - - ----- - -- - ----- - -- -- - --- - - - - - --
II. HISTORY OF E N GINE-DRIVEN FUEL PUMP DEVELOPMENT UP TO " C" PUMPS. - - -•-------- - - --- ~- -
III . HISTORY OF THE TYP.E "C" PUMPS ____ _ _ _ _ _ ___ _ ___ _ _________________ · ___________ _ _ __ __ _ _ ___ _
1. C- l--- - - - - - - ---- - - - - - - - - - - - - --- - ----- - - - - - -~--- - - - - - - - - - - - - ------ - - - - - - ---------- - -- -
2. C-2-- ~-------------- ----------------------- --------- ------ --------- - - -- - - -------- ----
3. C-5 ---------- - - - ----------------------~---------------- ---- - - - - - - - - ---- - - --- - --------
4. C- 3 _____ ___ ___ -.- __ ________ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
5 . C- 4 __ __ _____________________________________ _____ __ _____ ____ _______________________ _ _
6. Engine equipped to drive " C" pumps ___ _________ _____ _________________ __ ________ ____ ___ _
7. High-altitude work ____________________ ___ ____ ___________ · __ __________ _______________ · _ _
I v. GEAR PUMP THEORY - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
1. Gear arrangement _ __ _________ ______ ______ ______ ________ _______ ____________ ________ ___ _
2. Pumping principle ____ ___ ___ ________ ~ __________________ ____ ~ __ ___ _______ _______ _______ _
a. Volumetric efficiency ____ _________ ________________ __________________ __ _________ __ (1) Theoretical capacity ___ ______________ ___ __________________ ______ ____ ____ ________ ____ _ _
(a) Effective area _____ ___ _________ ____________ _ · __ __ ___ ___________ ________ ______ _
(b) Number of teeth __ __ ______ _________ _______ _______________ ___ ____ __ - ___ ___ ____ _
(2) Slippage _______ _______ ____ ___ ____ __ ____ _____ ___ ______ ________________ ______ __ _______ _
(a) Liquid pumped __ ~ __ ______________________ . _______ __ ____ ___ ____ __________ ___ __ ~
(b) Pump clearances __ __ _____ ___ ______________ ___ ________ ______ __ __ ____ _____ ____ c
( c) Speed of rota ti on _ __ _____ ______ __ ____ ______ ____ _____ __ __________ _____ _____ __ _ _
(d) Pumping head _ ___ __ _____ ____________ ______ ______ ______________ ________ - - - - - -
(e) Effect of turbulence ______ __ __ ___________________________ ______ __________ ____ _ _
3. Power. efficiency _______ ____________________ ___ __ _______ ______________ ______ ___________ _
4. Priming __ _____ __________ _________________ ____________________ ____ _ _____________ ____ _ a. Standard prime test ____ __ ______ ___________ __________ ______________ ____ _ - - - - - - - - -
5. Inter~al6:~~~~::1-::r~=~~:n~~~ ~i~~ ~~i~~~~~ = = = = = = = = = = = = = = = == = = = = = =; = = = = ;~ = = ~ = =·=·== = = == = = == =
V . DESCRIPTION OF THE "C- 5" PUMP ____ _ _ _ _ ___ _ __ - ___ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
l. Description of details __ __ _____ ____________ ___________ __________ ________ ______ _________ _
2. Clearances _____ ___ _______ ___________________________ ____ ___________ · _ - ·~ _ . _ . ___ - - - - - - - - - -
3. Design of the gears __ ___________ _______ __________ _____ __ --·~-- - - ~· __ : _· _ ~- '~---- - - -- - - ----
a. Gearteeth _____ ___ ~- ----- - -- - - - -------------- - - ---- - - ----"---- ~ - - -- - - ------ - - --
b. Number of teeth ________ ___________ -· ~ _________ _____ ~ ________ · _ __ _ -______ - - - - - - - - -
c. Pitch diameter and face ___ __ ____ ________ ____ __________ ______ - _ - _ - - - - - - - - - - - - - - - -
d. Gear center distance ___ ________________ _____ ______ __________ . ____ __ · __________ ___ _
e. Material_ __________ · ________________ ________ __________ ___ ____ ___ ______ ____ _ · ___ _
4. Capactty _ ____ ________________________ __________ __________ ____ · _ ~ · -- -----~ · ----- ------
5. Effi ci:~c~ ~l ~~;t~ic- ~ffi ;i~~1~; = = = = = = ~ = ~ = ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ = = = = = = = = = = = = = ~ = = = = = = = = = ~ ~ = = = = = = = = = = = = b. Power efficiency __ ____ __ ______ ______ ________________ ______ ____ · __ ~ ___ __ - - - - - - - - - -
6. Ability to prime _____ ____ ______ ____ ______________ _____ _____ __________ • ____ - - - - - - - - - - - - - -
7. Ability to run dry ___ ______ __________ ____ ______________ ___________ _____ __ __ - _ - - - - - - - - - -
8. Endurance __ J - - - - ---- -- ----------- - - ---------- - - - - -- - - - - ----------~-~ - - - ------ -- - - - - - -
VI. INSTALLATION ON THE ENGINE ___ _____________ _ ~ _ __ _ _ _ ________ _ _ _ _ _ _ __ __ :_::~- ---- ---- -- --
1. C- 5 pump ______________________________ ___ ~ - _____________ __ ______ · __ ______ ____ _______ _
a. General ___________ __ _________________ _______ ___ ____________ ____ ________ ____ ___ _
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b. Standard Liberty "12" ________________ ____ ____________ ______ ________ ___ _____ : ___ 12- 14
c. Wright model "E" a ·nd "_I "- --- -- - - -------------- - - ---- ---------- - - -- -------c -- - - 14
d. Lawrance "J- 1 "__ ___ ____ _____________ _____________________ ______ ___ __ __________ 14
e. New engines ___ ___ __________ ____ _ ~- __ ~ ____ __ _____ ___ _____ _____ ____________ _ .__ ___ 14
2. C-3 pUmP -- -- - - ---- - - - - - ------- - --- -- ------------ - - ---- --- - --- --- --- - -- ------ - - - ~---- 14
3. Engine t est __ ___ _______ ___ ______________ __ . ________ _________ ~ ____ __ · _____ __ ___ _ - - - - - - - - - 15
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VII. THE GEAR PUMP FUEL SYSTEM _ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 15- 24
1. Typical fuel system using gear pumps ___ __ __________ _____ __ _______ ____ __________ ___ __ ___ _ 15-16
a. Description _____ _________ ____ __ ___ __ -· ______ _______________ ____________________ _ 15- 16
(1) Relief valve __ __________ ____ ________ __ ____________ ____ __________ ____ ____ _ 16- 17
(2) Control cocks __________________________________________________________ _ 17
(a) Type E-1 cock ____ _______ ____ ______ ______ ____ _______ ___ ____ __ __ _ 17
(b) Type E- 2 cock ____ _____________________________________________ _ 19
(c) Type C- 1 cock ___ ___ _________ _________________________ . ______ __ _ 19
(d) Type C- 3 cock ___ _________ _ ~ ________ ______ ______ _______ _____ ___ _ 19
(e) Cable control_ __ ___ __________ ___________ ___ ____ _______ _______ ___ _ 19- 21
(3) Strainers ___ ___________ ____ _________________________ ___________________ _ 21
(4) Venting ____ ______ ____ _____ ___ __ ____ ___ ___________ __ ___________________ _ 21
(5) Tubing and connections ____ _________ ___ ____________ ________ _____ ___ __ ___ _ 21 - 22
b. Operation _________ __ __________________________________________________________ _ 22
(1) On the ground _______________________ __ ________________________________ _ 22
(2) In flight __ ___ _________ ___ _________________________ __ ____________ _______ _ 22
2. Fuel system for a supercharged engine _____ ___________ __ __________ _____ _______ ____ ______ _ 22- 23
3. Variations from t he typical system ____ _________________________________ . _________________ _ 23- 24
a. Removal of overflow indicator ______ __________ _______ _______ _____ _______ _________ _ 2~
b. Addition of hand pump _________________________________________________________ _ 23
(1) Centrifugal hand pump ___ __ _________ __ : __________ ___ ___________ __ ___ __ _ _ 23
(2) "Wobble" or oscillating hand pump _______ __________ ______ _______ ______ __ _ 24
c. Exchange of gravity tank for hand pump ___ ____ __ ________________________________ _ 24
VIII. I NSTALLATION IN THE AIRPLANE _~----- - ------- ------ - - - ---------- - - - -- --------- --- ------ 24- 25
1. General_ __ · ______________ ____________ _____________ _____ _______________________ _____ __ _ 24-25
2. Ground tests-- --------- ----- --------- ------ ------- ------ --~----- - - - --------- -- - ----- -- 25
a. Pressure gauge---- - --------------------------- - ---- ~ ----- - - - ------------- c ------ 25 b. Prime ____ _____ ______ _________ ___ _________ ______ _________ ___ _________ _______ __ _ 25 •
c. Relief valve __ ___ ____ ___________ ____________ _ .- _____________ ____________________ _ 25
d. Gravity tank _________ _____ _______ _____ ____ ___ ___________ ______ _________ ___ ____ _ 25
e. Gear pump capacity _______________________________________ ____ ____ _____ ___ _____ _ 25
f. Overflow indicator _ __ __ _______ ___ ____________ ___ ____________ __ _________________ _ 25
g. Packing - -------- - ------------------------- -- ------ - - - -- ----- --~----- --- - ------ 25
h. Level gauge ____ _____ ____________ ___________ _______________ ____________________ _ 25
i. Hand pump ___________________ ____ __________ ____ ___________ ____________ _______ _ 25
IX. THE GEAR PUMP IN SERVICE_ - - - - - - - - - - - - - - - - - - - ~ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 25- 27
1. General ____ _____________ ___ ___ _____ ____ _____ ______ __________________________________ _ 25
2. Trouble hunMng _____ _______ ______ _____ ____________ ___ _______ • __ ___ __ __ _____ __ ___ ____ : 25
a. Engine will not run on gravity __ ____ __________ ___ ________________________________ _ 25
b. Gear pump will not prime ______ ___ __ __________ ___________________________ ___ ____ _ 26
c. Engine will not run on pump _______ __________ _____________ _____ ___________ __ ____ _ 26
d. Engine will not run on e.ither gravity or pump ___ _______ ______ _____________________ _ 26
e. Engine will not run on " both on" ____ _____ ________ _________ _____ __ _____ __ ___ ____ _ 26
f. Engine will run on pump but pressure is too low ___ ___________ ___ __________ _____ ___ _ 26
g. Engine will not run at idling speeds __________ ____ _________________________ ______ _ _ 26
h. Engine will not run above a certain altitude ___ ___ ___________ ___ __ __________ ____ __ _ _ 26
i . Pressure is too high __ __________ ___ _________ _____ __________ ___ ________ __________ _ 26
j. The gravity tank accidentally empties __ ___ · ___ _____ ________ ____ ______ -- - - -- -- - -- 26
k. Packing leaks ________ ____________________________________ ____ _________________ _ 26
I. Gasket leaks ____ ____ ____ ______ ___ ____ ______ ___ __________________ _____ ______ ___ _ 26
3. Trouble in flight ____ ________ __________ _________________________________________ ___ ____ _ 26- 27
a. With typical fuel system _____ ________ _________ _____ ________ __ ___________________ _ 26
b. With supercharged engine fuel system ____ __ ~ __ ____ __________ ________ _____ ___ __ ___ _ 27
4. Preparation for engine overhaul_ ____ ________ _________ ___ ____ ____________ _______ ______ __ _ 27
x . OVERHAUL OF THE GEAR PUMP __ __________ __ ____________________ _ __ _____ _________ ___ _____ _ 27
1. General -- - - --------------------------------------------------- - ~ - ---- - --------------- 27
2. Repair ___ ____ _____ ___________ _____ ____ ___ _______ _____ __________ _____ _____ _______ ____ _ 27
a. Shaft clearance _____ _____ ______ ___ ___________ ___ _____ ____ ___ ________ ______ _____ _ 27
b. Side clearance __ __ ________ " ----- -- ---------- --- ------------ -- -- --------- -- - -- --- 27 c. Reassembly ____ ___ __________ __ ___ ___ · ______ ___ ___ _________________ _____ ____ ____ _ 27
3. Tests ______ ____ _______ _____ __ ______________________ __ _________ ___ ____________ ___ ____ _ 27
~ Capacity ___ ______ ___ _____ ____ __ ______ ______ __ ________________ _________ ____ ____ _
b. Dry run __ __________________________________________ _____ ______________ __ ___ __ 27
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4. Preparations for remounting ___ ___ ____ __ ___ __ _______ ______ ___ __ ____ ___ ____ ________ _____ _ 27
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XI. COMPARISON OF THE C - 5 GEAR PUMP WITH OTHER FUEL PUMPS _ _____ ___________ _ _ _ _ ______ _
1. General_ ________ _________ ___ _________________________________________________ __ - - - - - -
2. Pumps used for comparison ______ c ___________________________________ ________ ___ ____ ___ _
a. Commercial gear pumps ________ ____ _________ _______ __ ___ ___________________ __ .. __
(1) Wright gear pump ______________________________________________________ _
(2) Lawrance gear pump ________________________ · ____ _______________ __ _
(3) Pioneer Instrument Co. gear pump ________________________ _______ ________ _
b. Bellows pump _____ ____ · _______________ ________ ________ ~ ______________ _____ _____ _
c. Curtiss plunger pump ___ _______ ___________ __________ ___ ______________ _____ ____ _ _
d. Pump types ____________________________________________________________________ _
3. Qualities considered ______________________________________________ ___ ___ ______ ___ ______ _
a. Reliability ____________________________________________________________________ _
b. Freedom from fire hazard ______________________ ______ _____________________ ______ _
c. Ability to prime _____________________ ______ ________________ _____ _______________ _
d. Ability to run dry ____ ___________________ _______ _____ ____ __________________ ____ _ _
e. Indifference to changes in head _____________________________________________ _____ -
.f. Pressure regulation ___ __ __________________ ____ _______ ____________________ _____ __ _
~ Lightness ______ __________ _____________ ___ _______ ____________________ ____ __ ____ _
h. Ease of maintenance ____ _____________ ______ _________________ ________ _________ __ _
i. Adaptability to different engines __________ __ __________ __________________ _____ ____ _
J. Adaptability to a supercharged e ngine _________ _________________________________ __ _
k. Compactness _______ ___________________________________________ _______ _____ ____ _
l. Power effi ciency _· __ __ ___ _______ - ~ ____________ _____ __________ ________ _____ _____ _ m. Endurance _________________ _________ ____ ____ __ __________ ________________ ____ __ _
n. Resistance to deterioration ________________ ____ ___ ___ _______________ ________ __ ___ _
o. Cheap uess __________ ______ __ c __ __ __ __ _ ___ _____ _ _ ___ · ________ - - - - - - - - - - - - - - - - - - -
4. Tabulation __ __________ _____ _____________ _____________ ___ _______________ _____ ____ ____ _
XII. MISCELLANEOUS FACTS CONCERNING TYPE "C" FUEL PUMPS _ ______________ _ . _____ _ _______ _
1. Definitions ___________ _ ________________________________ _________ - - - - - - - - - - - - - - - - - - - - -- -
2. Engines equipped to drive C- 5 pumps _________________ ____ ________ ____________ ____ ______ _
3. Airplanes eq uipped with the C- 5 puinp __________________ __ _________ ___________ _____ ___ __ _
4. Drawing numbers and weights ___ ______________________ ____ __________________ __ ______ .. __
5. Change in various factors causing 20 per cent reduction of capacity under ordinary fligh t condi-tions,
"C- 5" gear pump _____ ____ _____ _________ _______ ________________________ __ ___ _ _
6. Power necessary to drive " C- 5" pump at 1,700 revolutions per minute against 3-pound pressure_
7. Priming the "C--5" pump ________ ____________________ ___ ______________________________ _
ILL USTRATIONS
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FIG. 1. Engine-driven fuel pump for supercharged engines, obsolete__ ________ _____________ ___ __ ____ 2
2. Type "C- 1" gear fuel pump ____ ______ _________________ _______________________ _________ 3
3. Type "C- 4" wind-driven gear fuel pumP- - -- ---------- - - --- --- ··--------·------·-- - -- - ------ 4
4. Effect of clearances on capacity, "C- 2" pump_________ ____ ___________ __________________ ___ ___ 6
5. Curves comparing pump capacity with engine consumption ___ _____ ________ · ________ - _ - - - - -- - - - 7
6. Standard prime test set-up _________________________ ____ __ _____________ ____________ ____ - _ 7
7. Curve of internal pressure variation, "C- 1" pump ______ ________________ • _ _ _ _ _ _ _ _ _ _ _ _ 8
8. T y pe "C- 5" gear fuel pump ____ _______________________ _______ ___ __ _______ .. ____ __ ,- ___ .. ___ 9
9: Capacity curves of "C- 5 " gear pump __ _______ _____ _____ __________ ________________ ____ - _ 11
10. Effi ciency curves of "C- 5 " gear pump____________________ ____________ ____________ _________ 11
11. Prime curves of "C- 5" gear pump ________________ __ _____ _____________ _____________ __ . _ _ 12
12. Rotation chart and arrangement of "C- 5" fu el pump drives _ __ ____ ____________ ___ ___ _____ __ 13
13. Liberty "12" engine showing "C-5" fuel pump and drive_ _____ _____________________ ___ ____ 14
14. Wright model "E" engine showing "C- 5" fuel pump and drive____________ _________ ____ __ ___ 15
15. Lawrance "J-1" engine showing "C- 5" fuel pump and drive_________ ____________ ___ __ _____ 15
16. Diagram showing information .necessary for engine designer in providing for "C- 5 " pump___ ___ 16
17. W- lA engine showing "C-3" fuel pump___________ ______ ____________________ _______ ____ _ 17
18. Typical fuel system employing " C- 5" fu el pump ____ ______ ___________________ - _ - - - - - - - - - - 18
19. " B- 1 " fu el relief valve sectionalized __ _____________________ ____________ __________________ 19
20. " E- 1 " fuel cock ______ ______ ________________ · _____ _________ ~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 19
21. Combinations of ." E " fuel cock contr;:il parts ___ ___ __ _____________________________________ 20
22. Supercharger fuel relief valve_ ___ __________ ____________ ________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 22
23. Flexible drive and pump mounted on Liberty "12" _______ __________ _________ ____ _ - _ - - - - - _ 23
24. Table of comparison of fuel pumps __ _________ ____ __________ ___ -. ______________ ; __ _____ __ _ 30
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ENGINE~DRIVEN GEAR FUEL PUMPS, TYPE" C"
I. NECESSITY FOR AN ENGINE-DRIVEN FUEL PUMP
Thus far, the following means have been employed
_on aircraft for transferring fuel from the tank or tanks
to the carburetor: Gravity, vacuum and gravity, air
pressure, and fuel pump. Each one of these methods
will be discussed briefly.
l. GRAVITY
Feeding an eugine by gravity is by far the simplest
and most reliable of all fuel systems so far devised, and
loss of pressure, and ffre hazard from bullet holes, and
the fact that leakproof tanks will not safely withstand
the necessary pressure due. to the thin metal walls.
Although new types of airplanes are never equippe:I
with air pressure, and existing types are being slowly
changed, air pressure is still used on more airplanes
in the Air Service than any other system.
4. FUEL PUMP
is used whenever practicable. Sufficient head to give Many types of fuel pumps ti.ave been devise::!, and
satisfactory operation has been so difficult to obtain, may be classified as wind-driven, electrically-driven, and
however, that only very few airplanes have been s'.l engine-driven. Wind-driven pumps have been driven
equipped. Low carburetors cause poor mixture by impellers of either the anemometer or the screw
distribution, due to great length of the intake manifold type. Anemometers are used in the Army only on
and most efficiently placed carburetors usually require . airship cars, driving a gear-type pump. They arc
a fuel tank location in the upper wing. Carrying the used on a number of Navy a irplanes, as well as air­entire
supply of fuel for an airplane in the uppe~ wing ships. Impellers of the screw type have peen used to
has a number of disadvantages; such as filling and drive various types of pumps, but mostly the .gear
increase in parasite resistance. Examples of full type.
gravity feed are the TW- 2 and TA-3, having their The only reas:in for using the wind-driven fuel pump
entire capacity in the upper wing, and the Messenger, OD airplanes is convenience 0£ installation. When no
having a single tank in the fuselage. provision has been made on an engine for driving a
2. VACUUM AND GRAVITY
This is the system most commonly used for auto­mobiles.
Pressure below atmospheric, obtained from
the intake manifold, from the oil pump intake, or by
means of a venturi tube in the slipstream lifts the fuel.
Automatic means for applying this vacuum to, then
venting, a chamber, causes the fuel a lternately to rise
from the main tank to the chamber, then flow to a
" nurse " tank above the carburetor. The failure of a
single ~alve is all that is necessary to make this system
inoperative, a condition considered highly undesirable
in an airplane. Another disadvantage is that it is
essentiall y a gravity system, requiring the "nurse"
tank to be high above the carburetor. In a DH, for
instance, the upper wing wo.uld not give sufficient
head to operate the Zenith US- 52 carburetor under the
worst conditions. The vacuum system has been used
in the LePere biplane, but it proved to be unsatis ­factory
and was soon replaced by wind-driven .fuel
pumps. The use of . a vacuum system on airships is
not so hazardous due to the ability to repair any
trouble which may occur in flight . Several "blimps"
have been reporte::I to operate satisfactorily on a
vacuum system.
3 . AIR PRESSURE
iuel pump, a wind-driven pump may be mounted
almost anywhere on the the airplane in the slipstream,
by making a simple bracket. vVhen it is necessary, as
with supercharged engines, to have t:10 pumps below
the gas level, the wind-driven pump has been the
solution, up to very recently.
The wind-driven fuel pump, however, while it will
always be useful, inust be considered a temporary
makeshift. It is uneconomical, due to low effici ency
and parasite resistance; the torque is low, making it
possible for a slight obstruction to stop the pump; the
impellers are easily broken; and it is difficu lt t:J get an
impeller which wi]I give the pump the necessary range
of speed between flooding the carburetor and supply­ing
the engine under all conditions of flight .
Electrically .driven pumps are too heavy when the
battery is considered. A magnetically operated pump
was developed at this field, but was never installed in
an airplane as it was heavy and uneconomical. A
motor-driven centrifugal pump was ·developed ma inly
for use on the NBL--1, having six Liberty " 12 " en­gines.
This was the only pump of large enough capacity
to do the work and which could be obtained quickly.
The use of electrical drive was justified due to the large
am:rnnt of ele-::trical energy provided on this airplane
for other purp:-ises. The only advantage electrical
drive has over engine drive is in starting, since it derives
Air pressure has been used more than any other energy outside the engine itself.
method for the main means of fuel supply. Next to The advantages of an engine-driven fuel pump are
gravity, it is the simplest system in use, and is a fair s'.J m!J.ny and s:J important that a great deal of effort
system for peace-time purposes . I n a crash the da.nger for a · number of years has been and is being expended
from fire is greater, but the inain reason why air pre3- on the pr0blem. S:ime of the advantages are greater
sure had to be abandoned for military purp ose~ is the 1 p ower efficieney. speed of pump increases as the con-
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sumption increases, less weight, no parasite resistance,
greater torque, any desired pressure, no tank pressure.
In spite of the work done, the number of successfur
fuel pumps driven by the engine is extremely sm!J,\l.
The difficulties are many, and past experience with
such a device is meager. Some of the necessities are,
ability to prime, adaptation to m!J,ny conditions of in­stallation,
packing gland, lubric!J,tion , provision for
excess pressure, light weight, reliability, mJtmting on
existing engines, ease of maintenance, ease of produc­ti
Jn, ease of inspection, corre ct capacity thr:rngh enti re
range of engine speeds, and ability t::i run dry (see p. 12).
At the time the engine-drive:1 gear pump was started ,
there were no engine-driven pumps in producti :rn in
this country, at least none that could be seriously con­sidered.
Since that time, however, t he Wright AerJ ­nautical
C)fpJration has a gear pump for its "E- 2 "
engine, and the Curtiss CJ. has a 3-cylincler plunger
pump of the Maybach type. in its "D- 12 " engine.
Recently a gear pump for the Lawrance 9-cylincler
radial was submitted for approval, and the Pioneer
Instrnm3nt CJ. has a gear pump for use on the Liberty
" 12 " which is incorporated in what they call the "K- L
fuel system."
As can- be seen· from the above discussion, the im­portance
of getting into production a reliable engine­clriven
fuel pump wis very great.
II. HISTORY OF ENGINE-DRIVEN FUEL PUMPS
AT M'COOK FIELD UP TO THE TYPE "C"
PUMPS .
When McCook Field was first started, a vane pump,
copied from a British design, was developed and first
installed in the D- 9-A. This pump was built into the
tank and was driven by a flexible tachometer shaft
from the engine. The flexible shaft was not strong
enough, the fiber vanes wore rapid ly, and the installa­tion
was heavy, so t hat this pump was soon abandoned.
The 4-cylinder "sylphon " punw was the next de­veloped.
It was like a plunger-type pump, except the
change of volum3 was obtaine:I by compressing a
metallic bellows instead of moving a pist ::rn in a cylin­der.
The only advantage which this pump had over a
plunger pump was the elimination of t he need for a
packing gland. This was flown a number of times, but
was abandoned, due to its weight, bulk, and difficulty
of maintenance. ·
Except for a magnetic type "sylphon" pump which
never passed the laboratory stage, the next pump to
receive attention was the well-known Duplex bellows
pump, or "sylphon " pump. This is a two-unit pump
which has had much use and with proper care is very
reliable. It has the spring discharge feature which is
at once its big advantage, and also a source of t rouble.
Its big advantages are automatic pressure regulation ,
ease of lubrication, and elimination of need for a pack­ing
gland. Its serious disadvantages a re weight, bulk,
difficulty of maintenance, production, and inspection.
Due to the use of an acid soldering flux in a large
order of these pumps, corrosion set in and after about
six months caused a number of bellows to fail, result­ing
in forced landings. Either bellows, however, will
supply an engine, so that if care is taken to see that
both units aTe in order the failure of one unit will not
cause engine failure. This pump is thoroughly de­scribed
in Power Plant Report Serial No. 1907 (A. S.
Information Circular, Vol. 4, No. 369, and Vol. 5,
No. 458), March 30, 1922.
It was clis3!J,tisfaction with this pump th'lt le:l t he
power-plant section to start the development of a gear
pump, which had, to start with, the advantages of low
weight and bulk, only two moving parts, dire ~ t relation
between speed and capacity through a wide range, and
high pressure. It was believed that a pump could be
made to have, in addition, a sati sfa ctory packing
gland, ability to prime coincident with ease of produc­tion,
ability to run with out lubrication , reliability,
FIG. I .- Engine driven fu el pun1p for supercharged engines.
Obsolete type
ease of adaptation to a ll conditions of installation,
and ease of maintenance and inspection.
Unfortunately gear-pump development got a bad
star t , clue to the haste resulting from a contract for
20 supercharged Martin bombers early in 1920. I t
was believed that for production, wind~driven pumps
should be replaced by engine-driven pumps, so that
a fter incomplete preliminary experiments, a pump was
designed for high a ltitude work . A photograph of
this pump is shown in Figure 1.
I
-r
,,
r j
/ '
fl. .
This pump had three sets of gears. One set pumped
fuel and vapor to the gravity tank. The gears provided
overcapacity to t.a ke· care of vaporizat ion which occurs
at - high altitudes. This vapor condensed in the
gravity tank, which was connected to the other two
sets of gears in series with each other, and thence to
the carburetor. The gears were all on one shaft and
were driven from the cam-shaft drive shaft of the
Liberty " 12." It was so designed that the inner set of
gears and housing could be used with a new shaft
and cover plate, making a single-stage pump for un­_
supercharged engines. This pump was a failure and
was replaced temporarily by Martin wind-drivei1
pumps.
3
The features of the " C- 1" design which di stingui shed
it from the later pumps of that type were:
(1) Relief valve included in the pmnp casting, and
adjustable with the pump in operation.
(2) "Bound Brook" bushings, having a graphite­filled
spiral groove.
(3) String packing, impregnated with graphite.
Two of these pumps were made by the National
Steel Products Co., of Dayton, and tests begun in
February, 1921. Seven more pumps of this· design were
made, one of which was mounted in the PW- 1,_Packard
" 1237" engine, for flight. This was the first flight test
of a "-C " type pump, and was entirely successful.
A number of considerations resulted in a redesign
in May, 1921, and construction of two pumps which
were delivered in September, 1921. In this design
the relief valve was removed, and the graphite insert
bushings replaced by phosphor bronze bushings. The
main reason for removing the relief valve was to make
it possible to use the pump for either direction of rota­tion.
Various materials for bushings were tried, but
none were found better than ordinary bearing bronze.
While those two pumps were being made, two impor­tant
changes in design had been decided upon through.
experiment: Firstly, the packing was changed from
graphited string to cork, and secondly, the idler-gear
bearings were changed so that instead of having one
in the cover and one in the body, with the shaft cut on
the gear, the bushing was pressed into the gear and a
stud pressed into the housing. The cork packing im­proved
maintenance, as the string packing had to be
prepared and placed very carefully, while the change
in bearings made manufacturing easier.
2. 0-2
These changes were incorporated in a new design
known as the type "C-2," which is in appearance and
except for minor changes, the same as the pumps of
this size put into service. An order for 15 was placed
and received in January, 1922. Nine of these were
placed on various engines, but only five were placed on
ships which ever took the air, viz, the Loening p ·w
--2B, Packard "1237," the parachute D9A, P- 74,
Liberty "12"; the night flying DH-4B, P-257, Liberty
"12"; the Boeing GA- 2, model "W- 1"; and the ill-
FlG. 2 fated C0-2, Liberty "12."
In order to have enough pumps for the recondition-
111. HISTORY OF THE TYPE "C" FUEL PUMPS ing of 10 Liberty "12 " engines, a rush ·order was
1. 0 -1 placed ju June, 1922, in the factory for 10 of these
The type "C-1," originally known as the "C-80 " pumps. Just before this time, a minor change was
engine-driven gear fu el pump, was designed as a pump, made in the idler-gear thrust bushing in the cover.
which, if successfu l, could be standard for a ll Aii This series can be distinguished from former·"C- 2"
Service engines up to 500 horsepower. The original pumps in a change iu the contour of the bushing boss
design shoivn in Figure 2 was started in October, 1920, in the cover, and by type "C- 2" being cast across
and complet ed in January, 1921. The latest pursuit the top of this boss. These 10 were completed in
engine at that time was the Packard, which was July, 1922. About half of these were actually flown,
designed to drive this pump. In May of the same one being used on· the "TW-1," P-200, Packard
year a pump drive for the Liberty "12" was designed "1237"; one on a Lawrence " J- 1," and the remain­to
mount on the crank case, replacing the lower part der on Liberty " 12 's."
of the cam-shaft drive-shaft housing. The splined Due to a constantly increasing demand for fuel
lower cam-shaft drive-shaft was replaced by a similar pumps, 40 more pumps of this design were ordered in
part with a beveled gear cut upon it at the top, which June, 1922, and deiivered by the Northside Tool
meshed with a gear integral with the shaft used to Works, of Dayton, t he following January. Nearly
drive the pump. This drive is still used, except the all of these pumps were supplied on a irplane contracts,
gear ratio is i1ow such that the pump has the same including the L. W. F. transports and t he Fokker
speed as the crank shaft while the original drive was, I PW-7's and C0- 4 's. Three were sent to the Navy
once and a half th.is speed. for use on Packard " 1237 " engi nes.
9570-J- 24'1'--2
3. C-5
It was discovered in February, 1923, that under a
condition of high-suction head, lowest idling speed,
and maximum pump clearance that the "C- 2" pump
. had insufficient capacity to operate a Liberty "12"
which has a high fuel consumption at idling speeds.
The capacity was increased by adding an eighth
of an inch to the face of the gears, and 10 pumps were
ordered from the National Steel Products Co., of
Dayton, from marked blue prints. A few other
changes were made, such as the use of stainless steel
gears to prevent rusting, increased hardness of the
idler gear to prevent burring the edges of the teeth,
and increased length of the drain bosses to eliminate
possible interference of the drain fitting. The new
design was given the symbol of "C-5" and has
entirely superseded the "C-2" pump. ·
In April, 1923, standardized drawings of the "C-5"
pump were sent to Washington for ·placing an order
4
more were ordered in March with one change, that is,
increase in face of gear from thirteen-sixteenths to
fifteen-sixteenths to. give greater capacity. It is con­templated
using all these pumps on model Wl-A engines.
5. C-4
The type "C- 4" pump is a wind-driven pump having
the same internal construction as the type "C-2"
pump. It was designed for use on airplanes unsuited
for other fuel systems and equipped with engines which
had no provision for driving a fuel pump. A photo­graph
of this pump is shown in Figure 3.
6. ENGINES EQUIPPED TO DRIVE "C" PUMPS
The use of the gear pump will be greatly increased
from now on due to the increased number of engines
equipped to drive it. The Packard "1237," Packard
"2025," Curtiss "D- 12," and Almen barrel engines are
designed to drive the "C-5" pump, and the Libe:-ty
.. :.
_ . _J
FIG. 3.- Type C-4 wind-driven gear fuel pump
for 100, as called for by the 1923 production schedule.
All the above changes were incorporated in these
drawings together with a general reduction of gear
clearances which made a much u+ore efficient pump at
only slightly increased expense. In October, 1923,
after thorough testing, the cover assembly, consist­ing
of aluminum with pressed in phosphor-bronze
bearings, was replaced by a phosphor-bronze cover,
nickel-plated, for the sake of appearance. This change
made a cheaper, though slightly heavier cover.
!. C--3
While the development of the ·above series of pumps
was going on, the type "C- 3" pump was designed for
engines between 500 and 1,000 horsepower, e!'pecially
the Wl- A. This pump was different in several respects
but the main difference was in the mounting flange, an<l
the increase in capacity by widening the face of the gears.
fI'wo pumps were completed at McCook Field in
February, 1923, for experimental use only. Fifteen
"12," Wright "E" and "I," Wright "R- 1," and
Lawrance "J- 1" have been provided with adapters
for driving it. No more "C- 2" pumps will be made,
this type being superseded by the "C- 5" pump. As
for the type "C- 3" pump, the Wl-A is the only engine
so far equipped to drive it.
7. HIGH ALTITUDE WORK
Another use for the" C-5" pump is with supercharged
engines. In order to get a fuel pump which is always
below the surface of the gasoline, a necessary con­dition
for high-altitude flights (see p. 22), wind­driven
fuel pumps have been used in the past. These
are only a makeshift, however, so that some other way
was sought to obtain a "drowned" pump. Many
different schemes have been experimented with, but
none have shown as much promise as a high quality,
oversize, spiral wound, flexible shaft. The best shaft so
far found is made by the Strand Co. of Chicago. Figure
21 shows this shaft mounted on a Liberty "12' engine.
•
To determine the breaking strength of one of these
shafts, one end was held, and torsion applied at the
other end by means of a lever of I-foot length, and
measured with a spring balance, arranged to give the
maximum reading for each test. At 6! foot-pounds
the driving end fitting of the spiral core bent due to
improper supporting. At 7.8 foot~pounds this core
end broke. The broken end was held where the wire
strands enter it and the torque applied again. At
13 foot-pounds this fitting split away from the wire
strands ; 6! foot-pounds corresponds to 2.2 horse­power
at 1,800 revolution per minute. The shaft is
rated at only one-fourth horsepower at this speed. The
power necessary to drive the pump and adapters at
maximum load does not exceed one-eighth horsepower,
so that the safety factor is very high.
Th ~ static strength tests were supplemented by run­ning
a pump by means of a flexible shaft, and feeding
into the pump-suction line various foreign matter which
might put an unusual load on the shaft in practice.
Two speeds were used- 250 and 1,700 revolution per
minute. Small bits of rubber, flakes of shellac, sand,
solder-globules as large as three-thirty-second-inch in
diameter, and flat spatters of solder as large . as three­eighth-
inch diameter by one-sixteenth-inch thick, were
fed into the pump with the gasoline without any
breakage of an.v kind. The pump slowed up a little,
and the shaft wound up until sufficient torque was
built up to snap the particles through the gears or break
them up.
Another test of this flexible drive was an endurance
test covering 1,350 hours of almost continuous running
at 1,700 revolutions per minute operating a "C-5"
pump at full load and with bends in the shaft as great
as any that would be allowed in service. The shaft
was taken down at the end of this run and the wear
could be detected only by careful inspection.
IV. GEAR PUMP THEORY
1. GEAR ARRANGEMENT
A gear pump may be composed of an internally cut
gear, with an externally cut idler gear meshing with it,
or two externally cut gears. The former method has
the single advantage that the center line of the main
shaft is on the center line of the body casting, making
a compact symmetrical mounting flange. The ex­ternal
arrangement only will be discussed, as it was
chosen for manufacturing reasons for the type "C"
pumps.
2 . PUMPING PRINCIPLE
The gear pump consists of a pair of gears rotating
within a housing which incloses them completely, with
the exception of the hole necessary for the shaft to
drive one gear, and the inlet and outlet. The inlet is
located at the point where the teeth are diverging, and
the outlet where the teeth are converging. Obviously,
the outlet and inlet may be reversed by changing the
direction of rotation.
Assume the pump inlet connected to a tank of liquid.
For simplicity, assume for the present that the pump
is below the tank. As the teeth diverge, the liquid is
carried in the direction of rotation by the "buckets"
5
formed by the space between two adjacent teeth in
each gear and the housing. As the teeth converge,
these buckets are emptied, discharging the liquid. If
the supply tank is below .the pump, the air in the
suction pipe is first carried out by the "buckets" and
the pump is said to be "primed."
Volumetric efficiency.- Due to clearances between
the housing and the sides and face of the gears, the
"buckets" leak, and the amount of leakage or "slip­page,"
determines the volumetric efficiency of the
pump. As in any other type of pump,
Theoretical capacity-Slippage
Volumetric efficiency
Theoretical capacity.
(1) Theoretical capacity.- Theoretical capacity is
the capacity based upon volume and is computed from
the following formula:
C _AXFXTX2XNX60=0519 AFTN gallon per
t- 231 .
hour in which,
C, =Capacity based on volume.
A= Effective area in square inches between two teeth.
F = Gea.r face, that is, tooth length, in inches.
T =Number of teeth.
N =Revolutions per minute.
(a) Effective area.- The effective area between two
teeth is considered in this report as the whole area
bounded by two adjacent teeth and the housing,
minus the minimum area between the root circle and
the end of the meshing tooth. This minimum area
occurs when the line between gear centers passes
through the center line of the meshing tooth. It has
been suggested that effective area be defined as the
whole area minus the area between the root circle and
the meshing tooth, when the latter first makes contact.
This, however, is not true of the idler gear, because
due to the backlash the teeth do not contact; leaving a
space for the liquid to escape. In the case of the
drive gear, the imprisoned liquid must be forced out
during the period between first contact and the point
of minimum area, some passing between the gear and
housing, and classified as slippage, and the remainder
joining the discharge stream, and classified as capacity.
The first definition gives an effective area slightly
greater, while the second definition gives one slightly
smaller, than the true effective area.
(b) Number of teeth.-The total area of a gear, as­suming
a constant pitch diameter of unity, varies ap­proximately
inversely as the number of teeth.
A two-tooth gear therefore would give the highest
volume for a given pitch diameter and face. The
Root type is really a two-tooth gear pump, the two
teeth of which have to be driven by a separate set of
gears.
A seven-tooth gear was used for the supercharger
gear pump, which may be seen in Figure 1.
(2) Slippage.- Due to the large number of factors
entering into a determination of slippage, it is ex­tremely
difficult or impossible to compute it. In the
case of the "C" type pumps, slippage was estimated
before the pump was built by comparison with other
gear pumps, which were carefully tested and meas­ured.
This important factor is dependent upon
nature of liquid pumped, pump clearances, speed of
rotation, pumping head, and turbulence within the
pump. These are taken up in detail, as fo llows:
(a) Liq'Uid p'Umped.- Surface tension, viscosity, and
density enter into very complicated relations, the
analysis of which have not been attempted. It is
known that the surface tension and viscosity of high­test
gasoline remain nearly constant under the usual
a irpla ne conditions. Density, however, has an im­portant
effect on slippage, and tests were made to
determine it quantitatively.
Three different specific gravities were used : 0. 710,
high-test gasoline; 0.820, kerosene; and 0.765, a mix­ture
of the two. A " C- 2" pump at 400, 1,200, and
2,800 revolutions per minute, with a suction head of
3 feet , and a discharge bead of 2 pounds per square
inch furnished the means of comparison. Capacities
are in gallons per hour.
'l'able showing increase i n capacity with increase in
specific gravity
400
J,200
2,800
g
62
162
16
75
183
20
79
194 .
6
By plotting capacity against specific gravity it was
possible to find out by interpolation the increase in
capacity clue to a change in the specific gravity of
high-test gasoline from 0.705 to 0.725, which could
occm in 24 hours at high summer temperature. At
400 revolutions per minute the increase in capacity
clue to this change is 50 p er cent; at 1,200 revolutions
per minute, 11 per cent, and at 2,800 revolutions per
minute, 6 per cent. ·
(b) P'Ump clearances.-For a given number of teeth
and tooth volume, there is one relation between pitch
d iameter and face which will give the least slippage;
t hat is, greatest efficiency. The least slippage is
obtained l".hen the "slippage perimeter" is the short­est.
The "slippage perimeter" is the perimeter of
t he section through the gear recess along the center
lin e of the bearings, minus the shaft diameter wherever
it is an obstruction to t he slippage. It has been
proven that this slippage is approximately the same
per inch whether it is cliainetral or side cl!larance. By
cliametral clearance is meant the difference in cl iaineter
between t he gear recess and the gear, and by side
clearance t he sum of the depth of gear recess, and t he
gasket thickness, minus .the width of the gear. Strictly,
t he "clearances;" that is, the distance between the
gear and the housing, assuming the gear centrall.'·
located, are half of the above.
In order to determine the effect of clearances on
slippage a series of tests were made on a "C-2"
pump, successively increasing the side clearance, and
then the cliametral .clearance. Side clearance was in­creased
by increasing the gasket thickness, and cliam­etral
clearance was increased by successively grinding
clown the outside diameter of t he gears. Capacities
rather than slippage were measured, for convenience.
Slippage erpials t heoretical capacity minus actual
capacity. The t heoretical capacity of a "C- 2 " pump
is 0.07715 mul t iplied by the revol utions per minute.
Figure 4 shows the results of these tests and is self­explanatory.
(c) Speed of rotation.-Slippage increases with speed
of rotation. Liquid will flow through a gear pump
with given clearances at varying rates, depending upon
the head and liquid density, with the gears not turning
at all, the cleara nces acting as an orifice. With the
gears turning, t his slippage is increased by t urbulence,
which increases with speed. In spite of t his, t he volu­metric
efficiency increases with the speed, up to the
.Point of cavitation, assuming a constant discharge pres­sure.
Curve "A," Figure 10, shows the increase in
efficiency with revolu t ions per minute · in the case of
the "C- 5" gear pump. The volumetric efficiency of a
gear pump drops so low at low speeds that it has to be
EFFECT OJ!= CLEARANCES ON CAPAC/TY
" C-2 "' PU~P ; "%f1 ro::Al CUA!"'NCE=l----l~ll!S.P~H s_v~
. . 0 175 ~ .. •
VARIABl.E SI.OE CL.EAli'ANCE'
.00 'IA M
IMIV/lfllLE QIAIUTtrAL CUAHAN&E
.0() ~.SID£ C~ARA#C~
.R/if.
000 "SOO 000
FIG. 4
ooo
designed .for t he lowest idling speed of the engine for
which it is designed.
F igure 5 shows curves comparing the co nsumpt ion
of a theoretical 500-horsepower engine with the ca­pacity
of t he "C- 5" pump in a t ypical installation ,
both plotted with revolutions per minute as the ab­scissae.
Note that the curves "A" and " B" are very
near together at 200 revolutions per minute, and di­verge
rapidly, until at I , 700 revolutions per minute
t he excess capacity is about 80 gallons per hour.
(d) Pmnping head.- As the pumping head increases,
the slippage increases, the cleara nces, of course, acting
as an orifice. Wit hin the ranges of pressure obtaining
in an airplane it is ver.v nearl:v t rue that suction and
.,.
I
1
7
discharge heads mll.y be added rn clctermiui.11g t he tota l
pumping head.
An idea of t he effect of pumping head on s lippage
may be obtained from Figure 9. For example, .at 300
revolu t ions per rniuute the slippage for a" C- 5" pump
is 12 gallons per hour greater with a 10-foot head
t han with a 2-foot head.
. Fuel Consumption Cur \/
of 500 H.P. tn~i ne. .
Prop. load at Sea LeveI.
. Capacity Curve of C-5 Pl.I
Mox. Clearanc~s.
Typical Installation._
C. Fuel Lons. Curve oT SOOtlP
'f'nj,i ne., ..Superc horj,ed.
·100
90
80
10
prime is dependent upou its abil ity to pump a ir. For­tunately
the suctio n heads are usua lly low in an air­plane,
and t he operation of getting fuel to the carbu­retor
for starting can be arranged to prime the pump
automatically.
(a) Standard prime lest.- In testing gear pumps for
prime, the set-up shown in F igure 6 is used . The
p roced ure is as follows : The valve in the overhead
horizontal line is set to pass approximately 5 ga llons
an hour. The valve beneath the overhead or priming
tank is opened and the t ime required for prime starts
at t his instant. The gasoline from this tank flows
through the horizontal line, corresponding to the car­buretor
line in an a irpla ne, and also t hrough the clear­ances
in the pump to the suction tank below, which
is the cause of t he priming. This tank is adjustable
in height from level with the pump to 6 feet below the
floor. Above and below the pump a re small sections Capacii)' Curve of
C-5 Pump.
Typical H~h ~llitude
flight condil1ons .
of glass tubing. When the flow reverses in the upper
t.o I glass section, the pump has primed. The lower sec­tion
simply ser v:es as a means for warning the operator
to be ready to snap the stop watch.
3o
2.o
0
FIG. 5
(e) Effect of turbulence.- No tests have been made I
to determine t he effect of turbulence 0 11 slippage. Tur- I
bulence does not need to be considered in design, as it
is JJegligible at low speeds at which pump capacity ap- 1
proaches nearest to engine consumpt!on , and an ad- 1
vantage at high speeds because turbulence will keep
down useless excess capacity. /,I
3 . POWER EFFI CIENCY
. output I As i.11 a n.\: other pump, power ~ffic1 e n cy= input ·
Assumrng !ugh-test gaso line to weigh 6 pounds per '
Ca-x 6 · . .
gallon, output=-w- X P=0.10 Ca P., ft. lbs ./m111 .,
in which Ca equa ls actual capacity in gallons per hour.
P equals total pumping head in feet.
4. P ltl l\UNG
FIG. 6.- Standard prime test set-up
It has been proven experimentally t hat once a pump
has primed, the length of suction line may be greatly
increased without t he pump losing its prime. As an
example, a pump which was scarcely able to prime
A gear pump of a size practical for use on an a ir- against 3 feet at 300 revolutions per minute did no
plane is too small to be an efficien t air pump. I n lose its prime when the suction line was increased to
other words, the safe running clearances in a small 9 feet. . · •
pump cause a slippage which is large in proportion to I Thirty seconds has been chosen as the maximum
t he theoretical capacity. The ability of a pump to , t ime which should be allowed in a prime test, although
under unusual conditions a pump has been known to
prime after three minut es.
8
b. Traps.- Suppose, in F igure 6, that the line leading
upward from the pump had a trap in it. By a trap
is meant a change in the slope of the tube from up­ward
to downward. Now, as the gasoline flows from
the priming tank through the pump it does riot com­pletely
displace the air, but flows down the sides of
the tube and pump, leaving the air column, which
extends from the trap downward through the pump
to the level of the liquid below, imprisoned by the
t rap, and this prevents it escaping to the air through
the priming tank. T he pump therefore is pumping a
little gasoline at the sides of the gears and a great
deal of air in the middle bf them, and the pump refuses
to prime. Even if the tube is horizontal at any point,
and not an actual trap, t he pump may not prime at
all. In an actual case, with a pump mounted so that
the gear shaft was vertical, the t ime of prime was
reduced from 60 seconds to 3 seconds by tilting the
pump 5 degrees, thus raising the outlet above the inlet.
Now, suppose that a trap is placed in the line below
the pump so that the top of the trap is above the
pump. The gasoline from the priming tank flows
through t he pump and some of it remains in the trap.
The trap is pumped out, lifting the column from the
supply tank part way toward the pump. Soon air
reaches the pump and the gasoline falls back through
the pump. Surging now takes place, and each time a
little air is forced out, until the pump primes. This
shortens time of prime slightly, but is not recommended
for installation for various practical reasons. This
lu 8
UJ
lL 6
"!
:r." 4
v
t.n z
0
scheme does not assist priming if there is a trap in the
discharge line.
c. Check valve as an aid in priming.- Priming is im­proved
by adding a check valve in the suction line, but
is not recommended unless priming can not be accom­plished
wit hout it, which might occur with a very long,
low, suction line. A check va\'\Te is of little or no
assistance if there is a trap in the discharge line.
5. INTERNAL PRESSURE VARIATION
The pressure within a gear pump varies from a
negative pressure at the inlet to a positive pressure at
the outlet. Figure 7 shows this variation along the
circumference of the gear recess of a "C- 1" pump.
The pump was prepared by drilling radially seven
! -inch holes, 30 degrees apart, through the wall
surrounding the idler gear. A primer tube one­eighth
inch outside diameter by 0.025 in ch wall by
2 inches long was pressed into each of these holes.
A mercury manometer was connected successively
to each of these tubes, the other tubes being plugged,
while the pump was run at 1, 700 revolutions per
minute p umping gasoline against a suction head of
13! feet and a d ischarge head of 9! feet. This combi­nation
was determined experimentally as one which
would give zero pressure at 90 degrees- that is, on the
center line through the gears. The reason why equal
suction and discharge heads fail to give zero pressure
at 90 degrees is believed to be due to different eddy
losses at the inlet and outlet.
~
~
~
~
~ 0
._ l
w
_/
~4
l
~ 6
bs :::>
If)
/0
/ v
,,, /
300
_/ /
/
60° 9o0 120°
FIG. 7.- Curve of Internal Pressure Variation-"C-1" Pump
150° 114°
OUTLET
•
V. DESCRIPTION OF THE "C- 5" PUMP
1. DESCRIPTION OF DETAILS
It is assumed in this section that the reader is fa­miliar
with Section IV. Figure 8 is a drawing showing
the essential details of the "C-5" pump. It will be
noted that only the small square end of the main shaft
is on the engine side of the mounting flange. This
makes the pump more readily adaptable to various types
of engines. The supercharger pump, Figure 1, had
the bevel drive gear keyed to the main shaft, so that
in mounting the pump, it was very difficult to get the
gears to mesh correctly. In the case of the "C- 5"
pump the drive mechanism is installed by the engine
manufacturer, making it a simple matter to remove and
replace the pump. Below is a detailed description of
each of the numbered parts.
1 is the body made of 8 per cent copper aluminum
alloy. Aluminum Is used for the sake of light weight
only. The ring or dowel shown· above the mounting
flange serves to center the pump on the engine, insur­ing
a true running shaft. The inlet and outlet bosses
are tapped to three-eighths inch Brigg's standard pipe
thread. This thread facilitates installation, as con­nections
may be made with ordinary pipe fittings, such
as nipples, ells, tees, etc. The three-eighths inch size
is correct for use with one-half inch outside diameter
copper tubing, which is used for engines up · to 500
horsepower.
9
2 is the main shaft bearing bushing, pressed into
the body and cover. The shoulder serves as a thrust
bearing for the gear. The bushing is made of phosphor­bronze,
as this proved to be better than any of the
materials tried, which are graphited bronze;" Genelite,"
an alloy of copper and lead; "Graphalloy," an alloy of
graphite and copper, with the graphite predominant;
monel metal, babbitt metal, cast iron, lignum vitae,
and "Promet," a heat-treated bronze. The difference
in diameter between the gear shaft and these bearings
is between 0.001 and 0.003.
3 is the driven-gear spindle pressed into the body.
This is made of stainless steel heat treated to a sclero­scope
hardness of 55 to 65. The shoulder serves as a
thrust bearing for the driven or idler gear.
4 is the stainless steel drive gear with integral shaft.
The integral construction is more expensive, but is
much safer, than keying or pressing the gear on the
having both bearings on the body side of the drive
gear, which resulted in a ba1ly worn bearing next t-J
the gear. This cantilever arrangement was therefore
abandoned.
The design of the gear . teeth is taken up under a
separate heading below.
5 is the cork packing. The first packing used was
cotton wicking soaked in a mixture of castor oil and
graphite. The castor oil soon washed away, but the
cotton fibers were impregnated with graphite and
effectively prevented leakage. Due to the care with
which the work had to be done and the time involved,
a more desirable packing was sought. Cork was next
tried and far surpassed expectations. The cork has
the conventional beveled ends and in addition a semi­circular
annular groove midway on the outside diame-
6cAR ,t:(J~L Pl/HP - TYPe c-s
~~~1~~~·-~--~--=--7~
FIG. 8
shaft. The shaft diameter, five-sixteenths inch, was ter which weakens the cork at this point structurally,
chosen as the smallest possible, to. give the least causing the inside diameter to be forced against the
opportunity for leakage between the packing and shaft with a greater pressure at the middle than at the
shaft, and yet be strong enough to prevent failure due ends, when the packing nut is screwed down. This
to obstructions such as small pieces of metal, core sand, packing, if properly adjusted at the start, need not be
etc., in the gears. touched before the next overhaul of the engine. Under
Although not shown in the figure, there is a shoulder laboratory conditions, this packing has prevented
cut on the sides of the gear eleven-sixteenths inch in even the slightest leakage without adjustment for over
diameter and 0.0015 wide to prevent the teeth cutting 300 hours.
the aluminum housing. Without the shoulder this cut- This packing is kept from rotating by radial V
ting occurred in the early pumps. It is believed to be grooves cut into the body at the bottom of the packing
due to the shaft on one side of the gear riding high in recess.
its bearing, while the shaft on the other side is low in 6 is the bronze packing nut. The length of this is
its bearing, or vice versa. so arranged that the cork is usually compressed
It would be a much simpler construction to have no enough to prevent leakage when the nut is at the outer
bearing in the cover, but a test was made of a pump end of its travel-that is, when it is flush with the
10
mounting flange-as shown in the illustration. This
gives it a quarter inch travel, which is s uffi cient adjust­ment
under ordinary condit ions for at least 1,000
hours of pumping. An an nular groove is cut around
the outside diameter just below the threads which is
drilled with four radial holes equally spaced, thus pro­viding
a passage for any gasoline which may leak past
t he packing,. because of neglecting to properly adjust
t he packing nut. This groove communicates with the
p acking drains described later.
It migh t be supposed from the drawing that the
packiug uut acted as a bearing for the main shaft, but
this is not true, there being a difference of one sixty­fourth
inch in diameter.
7 is the steel packing nut lock plate to which is
brazed 8, a straight steel p in. This assembly serves to
Jock the packing nut in position at a ny point in its travel,
to the nearest quarter turn. The lock is attached to the
body by means of the rounclheaclecl-screw 19.
8 is the packing nut lock pin. See 7.
9 is the driven or idler gear. This is made of
stainless st eel, and has the same shoulder design as
t he drive gear 4. The design of the gear teeth wiil be
taken up under a separate heading below.
10 is t he driven-gear bushing, made of phosphor­bronze,
and pressed into the driven gear.
11 is the only gasket used on t he pump and is. made
of vellum drawing paper, which is fairly uniform in
thicknes, 0.0025 to 0.003. Any other paper of exactly
t his thickness would probably do just as well.
12 is the cover plate, made of aluminum like the
body, with pressed-in-bushings, 2 and 20.
13 is t he two steel dowel pins pressed into the body
and having a "slip " fit in the cover. The object of
these pins is to maintain proper alignment of the main
gear bearing in the cover when the cover is replaced
a fter removal for any reason.
14, 15, and 16, are the No. 12 zinc-plated steel
washers, filister head 12- 24 zinc-plated steel screws,
and 0.032 galvanized-iron lock wire, r espectively.
17 is the three-eighth-inch iron pipe plugs, tem­porarily
placed in the pump inlet and outlet to hold
oil in , and keep dirt out while the pump is waiting
installation.
18 is the three slotted one-eighth-inch brass pipe
plugs used at the packing drain bosses, only one of
which is visible in the drawing. These bosses are
equally spaced.
19 is the No. 4-40 zinc-plated steel screw used to
hold the packing-nut lock plate 7 to the body .
20 is the t hrust bearing for the idler gear, made of
phosphor bronze and pressed into the cover.
2. CLEARANCES
The cliametral clearances, that is, t he difference in
diameter between the gear recess and t he outside of the
gear is 0.006 to 0.009. The side clearance, t hat is, the
depth of t he gear recess plus the gasket minus the gear
width is 0.0015 to 0.0045 at t he hub. The shoulder
thickness each side of the gear is 0.001 to 0.001 5,
making the sid e clearance at the teeth 0.0035 to 0.0075.
The clearance of the main gear shaft and its bearings,
as well as that of the idler gear and s pindle is from
0.001 to 0.003.
3. DESIGN OF THE GEARS
a. Gear teeth .- The tooth design is an orcliuary
generated in volute, having a 14!-clegree pressure
angle. A 20-clegree pressure a ngle was t ried with uo
apparent advantage. Generated rather t han milled
teeth are called for to give smoother ruuniug. Grind­ing
t he t eeth has been t ried , bu t t he cost was excess ive
a nd the advantage doubtful.
b. Nmnber of teeth.- Twelvc teeth were cli o:se11 as
t he minimum .11umber of teeth for which a standard
cutter could be obtained. As the teeth a re generated
in the latest design, t his reason does not uow apply.
Twelve teeth give slight ly smoother running than
seven.
c. Pitch diameter and face .- The "C-5 " pump has
a 1-inch pitch diameter and an eleven-sixteenth-inch
face. The face was decided upon after experiments
had been completed with t he " C- 2" pump having
nine-sixteenth-inch face, a figure which was based
upon judgment assisted by the measured efficiencies of
former gear pumps. The effective volume for one gear
is 0.022 by 12= 0.264 cubic inch . The "slippage
perimeter " for the "C-5 " pump is : (2XH)+4
(l + 0.08)- (3X-ft) =4.76 inches. The minimum perim­et
er for t his volume occurs when the pitch diameter
is seven-eighths and the face fifteen-sixteenths,
giving a perimeter of 4.38 inches. The "C- 5" pump
therefore has very nearly t he correct relation in this
respect, and tests show t hat the eleven-sixteenths face
actually gives less slippage than t he fifteen-sixteenths
face. The reason is that eleven-s ixteenths is t he ideal
face of a three-eighths priming tank inlet and outlet.
A wider face has portions of t he teeth not in -line with
the opening, and local high pressures at these points
cause increased slippage.
d. Gear center distance.- After a number of tests it_
was found that a center distance of 0.008 over t he
pitch diameter gave quiet running and also prevented
undue load on the bearings when the gears expa nded
.due to heat developed in dry running.
e. Material.- The gears are made of stainless steel
to. prevent rusting in storage and hardened to 55 to
65 scleroscope to minimize wear and prevent the teeth
from being hammered out wider than the recess.
Experiments were made with t he earlier pumps to
find the best material for the gears. One steel and
one bronze gear had been used for the supercharger
gear pump (fig, 1), b(1t after long running the bronze
became corrocl ecl, probably clue to electrolytic action.
Oi1e interesting material used, for t he idler gear
only, was bakelite, in combination with fabric, in the
form of the commercial products "Textoil " and
" Micarta." Both of these materials ran much quieter
with no loss in capacity or prime, and seemed to be
just the material for a gasoline pump. However, it
was soon discovered that, although gasoline bad no
visible effect upon it, water in t he gasoline caused it
to swell, ·increasing the face of the gear enough to cause
seizure.
Nickel steel was then used, heat-t reated to a ha rd­ness
of 35- 40 scleroscope. This hardness had to be
increased to 55- 65 clue to t he teeth hammering out,
11
increasing the face at the ends of the teeth enough to
cause them to cut into the aluminum housing.
"Stainless" steel was finally chosen to prevent
rusting.
4. CAPACITY
Figure 9 is a set of curves showing the actual capac­ity
of the "C-5" pump with maximum clearances
under varying conditions of pressure and speed of
rotation. High-test gasoline was used for these tests.
The speeds in the lower right corner were taken with
CAPACITY T~.5T.5 OP
GCAl2. F\JMP -TYPE: -C-5
3!!.liZ.IALllf4A
~UCTION HEt"O 3! f'TCT
Ote.icHFtRGI!. H~AO .!*iOWrt.
~ .(, I'~: -
.;\: ~ ("I: \V)
FIG. 9
t-f°
lt:,Ui?C!I IC:Eff'R.
TO COM61rtC.0
~OCTION 6'0l5CtfOlillit'
Ht.f'O~
a geared-down dynamometer to get more accurate
readings, and pressures were measured in feet of gas­oline.
The pressures for the other curves were meas­ured
by a mercury manometer.
A comparison of curves "B" and "D ", Figure 5,
shows again the effect of pressure on the "C-5" pump
above a speed of 1,100 revolutions per minute. The
pump 1s assumed to be on a theoretical 500-horsepower
engine, supercharged, during a typical flight to 42,000
feet altitude. Other assumptions are as follows: The 1
airplane leaves the ground with the engine "turning
up" 1,100 revolutions per minute. At 5,000 feet the
engine has a speed of 1,200 revolutions per minute;
at 12,000 feet, 1,400 revolutions per minute; at 37,000
feet, 1,600 revolutions per minute; and at 42,000 feet,
1, 700 revolutions per minute. Sea-level pressure at the
carb~retor is maintained by the supercharger.
To illustrate how the points of curve "D" were
plotted, take 1,400 revolutions per minute, at which
the· capacity is 80 gallons · per hour. At 12,000 feet
. the difference between tank pressure and carburetor
pressure is 29.9-19.0, or 10.9 inches of mercury, which
95704-24t-3
is nearly 5% pounds per square inch. To compare
curves "B" and " D " it is necessary to add 3 pounds
to this pressure, making 8% pounds. Tests show that
at 1,400 revolutions per minute, against 8Y2 pounds
total pressure, the capacity of the "C- 5" pump is
80 gallons per hour. This is 21 gallons per hour, or
about 20 per cent, less than the capacity against 3
pounds pressure.
Curve "C" merely shows the fuel consumption of
an assumed supercharged engine of 500 horsepower
during the same typical flight, assuming a carburetor
equal in specific fuel consumption to the one used for
curve "A." The break at 1,100 · revolutions per
minute is due to the fact that up to this point the
engine is throttled, but on leaving the ground full
throttle operation must be considered.
5. EFFICIENCY
Figure 10 is a chart showing the volumetric and
power efficiencies of the pump used in the capacity
tests. This chart is self explanatory.
ffl ( Y OF ~Al2. UMP- YPE -
URVt:'i'.\'
I NCRC.A~~ ll"t VOLUMC:T5ZIC fFRCtErtCY
WITH . lil?.P.M.
CON~TANT PR~:>!)Uef. Of 3ff. P-'e.2 SQ. IN .
uevE'B'
0?.Cli2f.A~E. IN YOLUME.TleJC E.FFICl~HC
YYITH INCli.E..Aoe. IN TOTA\.. PR:E5o~URI:;
COM~TANT SPEEO Of' 1100 li! .P.M .
UICYE 'c
YAJi?I ATIOl'i IN Powe~ t.FFI c ICNCY WITH ~P.M
CON!>TANT P~"":>;,Oi?e: Of_, ... PER 5.;t. JN.
A_V'E.R.AGf. TIGttTNE&'::t Of PACKIN'i NUT
uev(D
1NC'2.E.A~~:ni Powee. e.FF'ICIENCY WIT
INC'2e.A5E lri TOTAL P~~5!::1URE
CON~TANT ~~ED Of 1100 R .P.n.
AYl:.'?AGE TIGHTNE.55 Of PACKING NUT.
FIG.JO
0
a. Volumetric efficiency.- This was found by divid­ing
the actual capacity by the theoretical capacity.
Theoretical capacity=· 022X.6875X 12X2X60 N
231 .
= .09429 N gallons per hour, in
which N = r. p. m.
The slippage of the " C- 5" pump under ordinary
flight conditions, that is, 1, 700 revolutions per minute
at 3 pounds, is about 20 per cent of the theoretical
capacity, or 32 gallons per hour. This is at the rate
;1.2
of about 6.7 gallons per hour per inch of "slippage
perimeter."
b. Power efficiency.- ln finding the power efficiency
the "input" was measured on a variable speed one­fourth
horsepower electric dynamometer by weighing
the reaction of the motor field. The "input" included
the power necessary to operate the Liberty "12"
drive necessary in the test set-up. This drive absorbs
0.005 horsepower at 1, 700 revolutions per minute.
The "output" was computed.from the formula given
on page 7.
6. ABILITY TO PRIME
The "C- 5" pump with maximum clearances will
prime within 30 seconds against the suction heads
and with the speeds shown in Figure 11, under the
standard . prime condit ions, a descripti~n of which is
started on page 7.
F'l<IME T1=s/· OF C-5 GEAR !?UMP
WRYE :Jl(OWS RllflTtON ol" R. P.H.
TO M/6/fTllT Wff/CH ,PC/ff/'~££ .
PR/tte 11'1 .iO~M>S
FIG. 11
7. ABILITY TO RUN DRY
Another requirement imposed upon the "C- 5"
pump is running dry, that is, without the cooling or
slight lubricating effect of the gasoline, during a period
of about 30 minutes. This is due to the use of a 30-
minute emergency supply of fuel, which does not pass
through the pump, but goes to the carburetor directly,
usually by gravity. The pump therefore runs dry as
soon as the main supply is exhausted.
Much experimental work had to be done before the
pump would run dry without injury. Many types of
bearings were tried. The vitrious materials tested
were mentioned on page 9. The material finally
chosen was ordinary phosphor bronze. If the bush­ings
are carefully lined up as called for by the
drawings, any "C" type pump will run at least 10
successive dry runs of 30 minutes each at 1, 700 revolu­tions
per minute, with no measurable injury to the
pump. If the pump is below the gasoline level, 15 to
20 minutes more may be added to the safe dry-run
period, due to the fact that all gasoline is not immedi­ately
pumped out of the lines after the tank is empty.
8. ENDURANCE
An early criticism of the gear type of fuel pump was
the fact that wear would soon increase the clearances to
a point where the pump would be useless. This fear
was found to be groundless in the case of the gear
pumps of the "C" series.
A "C- 2" pump was taken at random from stock
and driven at 1, 700 revolutions per minute for 2,500
hours, pumping gasoline under conditions similar to
those of an actual installation. It was stopped at the
end of each 500 hours and bearing measurements
taken, also the capacity. After 500 hours the pump
was subjected to a series of 10 dry runs of one-half
hour each at 1,700 revolutions per minute. The fol­lowing
table gives the results of this endurance test.
'l'irne in hours
Start of test ...... . ............... . .... ..
500 ........... --- . ---- -- -- -- .... -- -- -- -- .
10 dry runs ................... .......... .
1,000 ... - . - . - -- - - - . - - - ... - -- - - - -.. - - - - - - -
1,500 ....... . . . . . ............... ........ .
2,000 ... ... "- ····· ··· ····· · - · · ------ -: .. .
2,500 ........ - .. . ..... . ... -- . - . . - . ...... .
A_verage Idler-gear Capacity
dll ve-.gear bearing gallons
cfe~~~~e clearance per hour
.0023
. 0032
. 00335
.0034
. 00355
. 0038
.0039
0. 0012
. 002()
.0024
.0029
.0033
. 0037
. 0040
}
Not
taken .
62
58
59
61
58
VI. INSTALLATION ON THE ENGINE
I. C-5 PUMP
a. General.- The "C-5" pump, as well as the " C-2"
pump, may be mounted directly on the "1921"
Liberty, Packard "1237," Packard "2025," Curtiss
"D- 12," and Engineering Division model "XW-lA";
and by means of special driving mechanism may be
mounted on the Lawrance "J-1," Wright "E" and
"I," and standard Liberty "12." Figure 12 is a chart
showing the · general location and arrangement of the
pump drives on the various engines, and the direction
of fiow.
To mount the "C- 5" pump on engines designed to
drive it, it is necessary only to exchange the pump for
the cover plate. The method of equipping an existing
engine with a drive for the pump will be explained in .
detail for each engine for which a drive is now available.
b. Standard Liberty "12."-The pump drive may be
mounted on_ either the right or left cam-shaft drive
shaft, although it is customary to mount it on the left.
Figure 13 shows the Liberty "12" with the pump
drive and "C-5" pump mounted on the left cam-shaft
drive shaft.
1'
13
eorATJON CHA ET AND Al2£!.ANGE/1C!YT or c. 5 rucL PUMP D!!?.IYC5
·• four
o @o
o , 0
' t '"'
PACKAE:.O IZ'J7 & ZOZ5
eme [l[YRTION
PUf'1F 110Uf'YT5 ON cNGINC
lAWl:eNC[ d-1
l:.CAE. t::.LtvATfON
PUf'1P !10UNT' ON DE/YC
D/2/Ve !10UNT~ ON t:NGINF:
PJeOf!> l!ND
YY~/GHT 110D. [ ~ I
510[ [LEVATION
PUMP MOUNT5 ON 01!!./YC
012/Ve /'70UNT!J ON F:t'IGINC
CU£Tl55 D-IZ LIBCl2TY-/2.. MODEL XWIR.
!)JDC t:U::.VATION /:?CAI:!!. CILYATIOfY BOTT0/'1 Vle'W
PU/'1P f10UNTj ON c!YGJNC PUMP MOUNTS ON Df?.IYC PUMF' /'10UNT5 ON eNGINC
OO!Ve MOUNT.5 ON ~NG/NE:: .
l"l6Xl8.t.£ 011/VG
4.1.JGl'llli.Y
FIG. 12
14
The following parts are necessary for this installation:
1 fuel pump drive assembly_ __ 027833
12 shims ______ ____ ___ ___ ___ 13238
4 studs _________ _________ __ _ MA- 5056
The following drawings are necessary:
Fuel pump drive assembly____ 027833
Bearing retainer_ _________ ___ 027831
Lower cam-shaft drive-shaft
assembly__ __ __________ ___ 027832
To mount the drive, proceed as follows:
(1) Remove one cam shaft assembly and both upper
and lower cam-shaft drive-shaft assemblies.
(2) Make the overall length of the upper cam-shaft
drive-shaft housing 7i inches. This requires cutting
3i inches from the lower end of 8109, "cam-shaft
driving-shaft· upper housing and flange assembly" in
FIG. "13.-Liberty "12" engine showing "C-5" fuel pump and
its drive
the case of the basic Liberty "12"; 3i inches from
13896 "cam-shaft and gun-control drive housing long,"
when Nelson synchronizers are used; and five-sixteenth
inch from 13897 "cam-shaft and gun-control drive
housing short,'' when a Nelson synchronizer is mounted
on the same cam-shaft drive shaft as the air pump. In
this case the air pump would be replaced by the gear­pump
drive.
(3) Rework bearing retainer 8072 to agree with
drawing 027831.
(4) Change 8208, "lower cam-shaft drive-shaft
assembly,'' to agree with drawing 027832. This
requires replacing the splined drive shaft 8141 by shaft
027830, furnished with 027833 and adding the reworked
bearing retainer 027831.
(5) Replace four studs No. 131 in crank case by four
studs MA-5056.
(6) Mount 027832, obtaining the proper mesh of the
gears by means of shims 13238.
(7) Mount drive assembly 027833, getting proper
mesh of pump-drive gears by means of shims 13238,
also 027842, 3, 4, and 5. (See drawing 027833.)
(8) Reassemble remainder of engine, using the
shortened cam-shaft drive-shaft housing.
(9) Replace the cover plate on drive assembly
027833 by the fuel pump.
c. Wright Model "E" and "!."- Figure 14 shows a
model E engine with the fuel-pump drive and a "C-5"
pump in place.
All the parts needed for this installation are included
in the "Fuel pump drive assembly" X- 43895. The
drawing X- 43895 is the only one necessary.
To mount the drive proceed as follows:
(1) Remove right-hand cam-shaft drive-shaft hous­ing
assembly, both upper and lower, and cam-shaft
drive shaft upper.
(2) Replace the shaft collar which is assembled to
the top of the lower drive shaft by means of a taper
pin, by X- 43899, "driving gear."
(3) Reduce length of upper cam-shaft drive-shaft
casing assembly to length shown on drawing X- 43895.
(4) Separate assembly X- 43896 from X- 43895.
(5) Reassemble engine, using casting X- 43897, sepa­rated
from X- 43895, in place of the cam-shaft drive­shaft
housing lower casting, using the same nuts, pack­ing
ring, and packing, and shortened casing assembly.
(6) Reassemble X-43896 to X- 43895, obtaining
proper mesh of bevel gears by means of shims X- 42103
and X- 42104 between assembly X- 43896 and housing
X- 43897,. and by means of shims X- 45309 and
X-45310, between housing X- 43897 and the upper
crank case. By removing cover X-43903 it wiil be
possible to see that the gears are meshed properly.
(7) Replacing the lock wires will complete the in-stallation
of the drive. ·
(8) Mount the pump as shown on the installation
drawing X- 43895.
d. Lawrance "J-1."-Figure 15 shows the drive and
C-5 pump mounted on this engine. Fuel-pump drive
assembly X- 42824 is the only part necessary besides
the pump. itself. It is necessary only to remove the
cover plate from the right side of the intake and mount
the drive so that the pump inlet and outlet will be in a
horizontal line. It is possible to mount the drive in
three positions, but only two are correct.
e. New engines.-The information necessary for the
engine designer in order to equip his engine with the
means for driving the "C-5" pump is shown in Fig­ure
16.
2. "C-3" PUMP
At present this pump is used only on the Engineering
Division W- 1- A 700-horsepower engine. Figure 17
shows the correct installation for the pump on this
etigine. It is necessary only to replace the cover plate
by the pump. It can be mounted only one way.
15
FIG. 14 .-Wright Model " E" engine showing 11 C-5" fuel pump m1d dri ve
3 . ENGINE TEST
During t he testing of the engine elther on the dyna ­mometer
or the torque stand the pump must not be
a llowed to run dry. It should be connected up so that
it will pump gasoline . Before leaving t he t esting rig
the plugs must be inserted in the inlet and outlet of
t he pump to keep dirt out. If the engine is not to
be installed at once, the pump gears should be oi led
before inserting the plugs.
VII. THE GEAR PUMP FUEL SYSTEM
As one of the main objects in developing the gear
pump was to replace the bellows pump, it is natural
t hat the gear pump is most commonly found in the
standard bellows-pump system, with certain differ­ences.
Unlike the bellows pump, which provides auto­matic
pressure regulation, a by-pass line containing
a relief va lve has to be used with the gear pump.
The only other diffe rence is t he necessity for greater
precaution in providing for priming in the case of
the gear pump. This syst em is described in t he next
paragraph.
]. TYPICAL Fu 1; 1., S YSTEM USING G1; 1ui PUMP
F igure 18 is a photostat showing t his typical system.
a. Descri plion.- Gasoline flows to or is lifted by t he
pump from the ma in tank, passing through the stra ine r.
The pump forces it t hrough a three-way cock to t he
carburetor. The t hree-way cock is connected a lso to
the gravity tank. The gravity tank has aD overflow FIG. 15 - Lawrance J- L engine showing " C-5" fuel pump and drive
16
line leading from the top of this tank to the top of the
main tank through an overflow indicator.
The three-way cock may be turned so that both, or
either, the gravity tank and pump are connected to the
carburetor, or both may be shut off from the carbu­retor
and from each other. When the pump is con­nected
to the carburetor, but not to the gravity tank,
the excess from the pump builds up a pressure which
is relieved through the by-pass line cont1Lining a
spring-loaded relief valve. The pump excess is thus
returned to the top of the main tank.
Two lines lead off from the line connecting the three­way
cock and carburetor; one leads to the pressure
gauge on the instrument board, the othei· through ~
shut-off cock to -the pump used for priming the engine. ·
The discharge of t his pump connects to the proper
points in the intake manifold.
The vent line, connected into the overflow line, and
the carburetor, p ump, and strainer drains c·omplete
the system.
The note calling for a constant slope in the pump
intake and discharge lines is necessary to insure the
II
3Z
pump priming. This applies only when the level of
gasoline in the main tank, at the lowest point at which
the airp lane would ever take off, and with the tail
skid on the ground, is below the pump. The necessity
for t h is slope is explained on page 7.
Following is a description of the parts other than the
gear pump, which make up the ·system:
(1) Relief valve .- Figure 19 gives a full-size view of a
sectionalized relief valve of the "B-1" type, for use
with the "C- 5" pump. It is made in the form of a
tee for convenience of installation. The " run" of the ·
tee forms a part of the pump discharge line. The
"branch" of the tee allows the passage of the excess
fuel back to the main tank. These three openings
are equipped with standard three-eighths inch pipe
threads, permitting t he use of one-half inch outside
diameter copper tubing, with proper connections.
The body is made of a standard casting alloy of
aluminum and copper. The ball is made of Mone!
metal to minimize corrosion. The spring is of phos­phor-
broi1Ze wire and rests upon the ball. The cage,
adjusting nut, lock, and cover are of brass.
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Fm. 16.- Diagram showing information necessary for engine design in providing for 0 -5 pump
NOTES
1. This pump is designed for engines up to 500 horsepower.
2. Pump should be mounted as low on the engine as possible.
3. Pump should be mounted so that a line through the outlet and inlet is vertical, the inlet being at the bottom.
4. Pump must be mounted so that inlet is below or on a horizontal line with the outlet. In case the inlet and outlet are parallel with the propel­ler
axis, the ou tlet must be toward the propeller end.
5. With the rotation shown above, the pump outlet will be as shown. With the opposite rotation, the outlet will be on the opposite side of
the pump.
6. Pump speed must be not less than 200 revolutions per minute at lowest engine-idling speed, nor over 2,200 revolutions per minute at the
maximum engine speed.
17
The adjusting nut is shown at the top of its travel.
The top of the lock, which holds the adjusting nut
at any point in its travel, is barely visible just under
the top inside of the cover. The adjustment and spring
are so designed that with the nut as shown, the valve
will by-pass 100 gallons per hour at a hydraulic pres­sure
of 2 pounds; and with the nut screwed down to the
stop, 100 gallons per hour is discharged when 4. pounds
pressure is applied. This range is .sufficient, except
in very unusual installations, to make it possible to
get a gauge reading of 3 pounds at full revolutions per
minute.
To adjust this valve, remove the cover, take out
lock, and with a screw driver turn right-handed, or
clockwise, to increase the gauge reading, and vice versa.
The amount of adjustment must be in half turns, so
that the lock may be replaced. ·
For engines above 500 horsepower, the "B-2 " relief
valve is used, so that this valve is used with the "C- 3"
pump. This is identical in construction with the
"B-1" type, except in size. It has one-half inch pipe
thread openings, and is larger in all respects.
A special relief valve for use with supercharged
engines will be described later. ·
The location of the relief valve is important. Al­though
not always praeticalf' the relief valve is best
located above the level of the carburetors, so that in
case the ball is held off its seat by dirt carelessly left
in the system, there will be a head on the carburetor.
When the location shown in Figure 18 is not high
enough, the easiest way of accomplishing this is to tee
the relief valve line into the overflow line, below the
overflow indicator. Care must be taken so that the
large flow through the relief-valve line will not back
up the overflow line into the indicator, and therefore
give a false indication. Placing the tee 6 inches below
the indicator will prevent this, unless the stream is
directed up the overflow line by improper pipe fitting.
(2) Control cocks.- Commercial metal-key cocks are
not suitable as pilot-controlled cocks due to possibility
of sticking at a critical time, and because they leak
seriously after much use.
Control of this cock is obtained by a steel tube
acting in torsion between a handle in the pilot's cockpit
and a fittfng which engages a yoke attached to the
cock, as shown in the figure. This fitting and yok e are
designed so that it not only acts as a universal joint
but also permits longit(1dinal movement which is
essential to prevent the stem being pushed off its seat
by errors in installation or deformations in the air­plane
structure due to flying or landing str esses.
Another universal joint is often needed at the handle
end of the control rod for convenience of installation.
Figure 21 shows the various methods for arranging the
parts of this control to suit every condition.
FIG. 17.- Wl-A engine showing" C-3" fuel pump
(a) Type "E- 1" cock.- This cock is shown sec­tionalized
in Figure 20. The aluminum body is in the
form of a tee, the branch of which is in all installations
connected to the carburetor. · The left outlet of the (b) Type "E- 2" cock.-This type fa identical with
run is the gravity connection, while the third opening the "E-1" cock described above, with the exception
is connected to the pump. By comparing this with the I of size. The "E-2" cock is designed for use with
dial shown in Figure 18, the operation of the cock is engines between 500 and 1,000 horsepower, and would
apparent. be used with the "C-3" pump.
The essential feature of this construction is the cork- (c) Type" C-1" 3-way cock.-This type was designed
faced stem. The cork is made up in a unit consisting for use with the bellows fuel pump, but has been used
of layers held together by means of a special resilient in the gear-pump system, as the "E- 1" is only a recent
cement. · The unit is pressed onto the stem, which is development and has been av.ailable only a short time.
knurled and shellacked. As an extra precaution pins The "G-1" cock has only four positions while the "E"
are driven through the upper stem flange into the cork. type has five.
The correct taper is then carefully ground. The The "off" position of the "C" type is not a true
double-compression coil spring serves two purposes- "off" position, as the carburetor is shut off by connect­holding
the stem into the body, and giving the spring ing the gravity and pump together. This serves to
action necessary for the star-shaped plates (shown only shut off the engine but causes trouble in the hangar
in section) which ~ake it possible to "feel" the five by causing the gravity tank to drain at a rate of from
positions when the cock is operated. 1 to 8 gallons per hour through the pump to the inain
.~ ~
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!)!AGRAM Of TYl>IC~l FUEL SYSTEM
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FIG, 18-'l'ypical fuel system employ ing " C-5" fuel p ump
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19
tank, or to the floor if 1,he main tank is full and the
vent is low ; and also ma kes it necessary to fill the
gravity tank by hand to start the engine.
The dial for the "C" type has a note cast upon it at
the "off" position, reading " Leave at 'run' when not
in ·use." If this note is followed, the pmi1p is connected
to the carburetor, thereby cutting off the gravity tank.
Two troubles have been experienced with this arrange­ment
and are the cause for the development of the
" E" _type, which, as explained, has a true "off" posi­tion.
Both the pilot and mechanic forget to follow
the instructions to turn to " run " when a ship comes
in. With the bellows pump, this would not make any
difference if the check valves were tight. With the
gear pump, however, the grav ity tank promptly drains
thrnugh t he gear clearances to the main tank.
FIG. 19.-" B-1" fu el relief valve sectiomlizcd
The second trouble occurs when the carburetor is
below the level of the gasoline in the main tank,
combined with a leaky carburetor float-chamber inlet,
or with a carburetor having the float chamber forward
of the jets. Under these conditions, when instructions
a re followed; that is, when the handle is turned to
" Run, " the main tank drains through the pump,
float chamber, jets, and carburetor drain to the hangar
floor. If this condition occurs, and an "E- 1" type
cock is not available, the only solution is to put a cock
in the carburetor line. This should be for t he use of the
mechanic only.
(d) Type "C- 3" cock.- This type is a recent design,
replacing the "C-1" cock. The operation and use is
the same for both, but the method of manufacture of the
' 'C-3 " is an improvement.
(e) Cable contr.ol.- The use of three-way cocks is
not advisable on la rge a irp lanes when cable co ntrol
to the cocks is necessary, for t he reason that it is
difficult to feel the cock positions, and the length of
cable is difficult to maintain constant. For these
reasons two shut-off cocks are used to repla<'.e one
three-way cock. One shut-off cock is placed in the
pump discharge line, the other in the gravity line. The
downstream sides of the cocks (assuming the gravity
tank emptying) connect into a tee, the branch of which
connects to the carburetor. Each cock has a pulley
attached to it which is connected by cable to the pilot's
contr'ol lever.
An important point in this arrangement is the loca­tion
of the stops, which are 90 degrees apart and indi­cate
to the pilot the "On" and "Off" positions.
FIG. 20
These stops are placed near the cocks. If they were
loca t ed on the pilot's levers, any change in length of the
cable due to installation, or distortions clue to flying
stresses, would prevent the holes in the stem from
·registering with the holes in the body, thus creating a
restriction to flow which might easily stop the engine.
With the stops at or near the cock, full flow or complete
shutting off is assured when the pilot turns the lever
until it stops.
(3) Strainers.-Proper screening of the gasoline,
important in any fuel system, becomes of great im­portance
in a gear"pump system, as abrasive foreign
matter, such as metal filings and core sand, score the
aluminum housing and under some circumstances
will actually jam the gears, causing the pump shaft to
twi st off. It is known that pa r ticles of rubber, solder
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DIAGRAMS SHOWING INSTALLATIONS OF FUFL COCKS TYPE "E"IN THE TYPICAL SY5TEM
FIG. 21.-Showing combinations of "E" cock control parts
'\
7-27- 23
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21
beads, dried shellac bits, fairly large in size, will pass ·
through the pump without injuring it, but sand or clay,
tightly packed, or metal chips, or a rag, will cause the
gears to jam. Only gross carelessness, therefore, will
endanger the proper functioning of the pump.
Following the gas line from the field tank wagon to
the carburetor will give a good idea of the problem of
screening.
The taqk filler unit contains a 50-mesh brass-wire
screen. It is true that this is usually removed in filling
the tank at an airdro.me to speed up the work, but in
cross country "flying, where it is necessary to use
gasoline,· the history of which is upknown, the filler
screen becomes important.
A properly designed sump, like the one shown for the
main tank in Figure 18, will catch any large heavy
debris, sometimes built into or acquired by a tank, and
all of the water. Some of the small particles may enter
the outlet tube and flow to the line strainer.
The line strainer shown in Figure 18 is the type
"C- 1 " strainer, of recent design. This strainer
consists of . an aluminum casting with a brass ring
threaded into it at the lower end, and threaded inter­nally
to take the bronze cover. The latter has a one­fourth
female pipe thread, so that a plug or drain cock
may be. added. The basket screen is 60-mesh monel­metal
wire and is removable. To increase the screen
area without increasing the outside dimensions, a
conical screen with the apex .at the top is joined to the
cylindrical screen at its lower end .
The "C-2" strainer is similar to the "C- 1 " type,
but designed for use with engines from 500 to 1,000
horsepower. The cover is too large to be threaded
satisfactorily, so it is held to the body by a yoke.
The function of the line strainer is (1) to protect the
fuel pump; (2) to act as a water pump for the fuel sys­tem,
sometimes including the main tank; and (3) to
catch the bulk of the foreign material passing the
main-tank sump.
From the line strainer the gasoline flows through the
pump and three-way cock to the screens provided in
or with every carburetor. The Zenith US-52 car­buretor
used with the standard Liberty " 12 " has a
strainer which is separate, but especially designed for
it. All the Stromberg carburetors have built-in
strainers. These act as the "bodyguard,'' so to
speak, of the jets.
A screen is placed at the inlet of the special super­charger
relief valve, which will be described later.
(4) Venting.-The venting shown in Figure 18 has
proven to be the' best. Inasmuch as the tops of both
gravity and main tanks are connected together by the
overflow line, it would appear at first sight as if a
single vent at the top of either tank, or teed off the
overflow line at any point in its length "'.Ould be suit­able,
provided the overflow line slopes constantly down­ward.
However, if the top of the gravity tank is
vented and the gravity tank is overflowing, the restric­tion
in the overflow line builds up a slight pressure in the
gravity tank, causing gasoline to be forced out the
vent. Sometimes the vent line may be raised high
enough conveniently to prevent this, but the method
shown is the me.re certain. Taking the other extreme;
that is, a single vent placed at the top of the main tank,
a siphon is formed when the gravity tank overflows,
which would, in many installations, cause a reduced
head on the carburetor, sufficient to stop the engine.
The venting shown ·in the typical system is a satisfac­tory
compromise. The possible siphon is broken at a
point high enough to prevent serious loss of head at
the carburetor, and there is, under all except the most
unusual conditions, a sufficiently low restriction in the
overflow line from the vent tee to the top of the main
tank to prevent the gasoline raising to the top of the
vent.
Note that the overflow line comes in at the rear of
the gravity tank and passes diagonally across the tank
to the upper, opposite, forward corner. It will be seen
that this arrangement makes loss of gasoline from the
gravity tank through the overflow to the main tank
impossible, regardless of the positions which the airplane
may assume.
When two main tanks are used they should be con··
nected to act as one tank. A vent line will be necessary
to connect the tops of the two tanks.
(5) Tubing and connections.-The tubing for this
system is seamless copper, as follows: All sizes refer to
outside diameter.
i"-0.025 Wall. Used for primer tubing only.
l"- 0.032 wall. This is used for vent lines, the
fuel-pump drain, and pressure-gauge line.
!"-0.032 wall. For carburetor vent lines, and
for the main lines supplying engines not exceeding 300
horsepower, and when the lines are not unusually long
or the pumping head unusually great. The relief valve
and the overflow lines are one-half inch for this engine
size.
~"-0.032 wall. For r elief valve and overflow
lines with engines under 300 horsepower, and for all
main lines supplying engines having a maximum horse­power
between 300 and 600.
5/8"- 0.047 wall. For all main lines supplying
engines having a maximum horsepower between 600
and 1,000.
3/4"- 0.047 wall. This and larger sizes are used
only on multi-engine airplanes not having individual
fuel systems for each engine.
Connections are made flexible only when absolutely
necessary. Promiscuous use of flexible connections is
not permitted due to the high cost of maintenance of
the rubber joint. No metallic flexible joint which is
suitable for military airplane use has yet been devised.
Flexible joints are necessary at each end of tubing, one
end of which is attached to the engine. The advisability
of flexible joints at any other point is open to question,
although at present, for the sake of safety, they are
used at each end of a line joining parts which are sub­ject
to relative movements or unusual vibration.
Flexible joints are not used for lines the ·breakage of
which would not cause engine failure or create a fire
hazard in flight. A pump drain, or vent, would be
of this class. Flexible joints are not used on primer
tubes.
22
b. Operation.- The operation of t he typical system
shown in Figure 18 will be expla ined both from t he
·mechanic's standpoint and t hat of the pilot. This
explanation applies to normal operation only . Trouble
hunting is considered in Section IX.
(1) On the ground.- In star ting an engine eq uipped
with ·a gear pump, turn the. three-way cock to the
" Start- both on" position. This not only provides
t he carburetor with gasoline, but also allows gasoline
to flow through the pump, which permits it to prime
as soon as the engine starts: When the overflow indi­cator
shows that the gravity tank has been filled by
the excess from the pump, the cock should be turned
to " Run- pump on." The pressm;e gauge sh ould
then read between 2t and 3t pounds at three-fourt hs.
t he maximum engine speed. If necessar y, the r elief
Fin. 22.- Superclmrger fu el relief va.lve
valve should be adjusted to obtain this pressure (see
p. 16). If more t han five minutes · is consumed in
starting the engine, it would be advisable to t urn t he
three-way cock to t he "Gravity on" position, while
starting, . to prevent the gravity tank from emptying
through the pump gears to the main tank. If t his is
done, it is necessary to turn the cock to the "Start"
position for a few seconds to .prime the pump before
t urning to the " Run " position. This is not true, of
course, if t he level of gasoline in the main tank is on
a level with , or above, the pump gears. In t his case
the cock may always be turned to " Gravity on " for
starting.
(2) In jli:ght.- Assuming t he gravity head suffi cie1H
for full-throttle operation, t he p ilot may take off with
the cock at either t he " Run " or the "Start " position .
The advantage of the former is that t he p ilot never
has to touch the fuel system during a flight, barring
accidents or the main tank going dry. The "Start "
position is probably safer for the take-off. In case of
main system failure during this critical period, the
gravity tank. will automatically come into action.
Upon reaching a safe altitude t he cock should be
turned to "Run " after noting that the overflow indi­cator
shows that t he gravity tank is Qv.erflowing.
In case the main tank goes dry, the cock must be
quickly turned to "Gravity on." Finding a landing
field may then be accomplished with the assurance that
the full capacity of the gravity tank is availa ble.
The engine may have to be throttled due to insuffi cient
gravity head ..
Upon landing, the engine should be shut off by
turning to the "off" position. In the case of the
"C- 1" cock it is necessary to turn to " Run " a fter
the engine has stopped. (See p. 19.)
2. FUEL SYSTEM FOR A SUP E RCHARGED E NGINE
There are two reasons why a fuel system for a
supercharged engine is different: (1) Because the
supercharger pressure is a utomatically applied to t he
gasoline within the carburetor float chamber, and (2)
because usually an altitude is reached with a super­charger
at which high-test gasoline can not be lifted
by suct ion due to the in crease in its vapor pressure.
Carburetor float mecha nism cpuld be designed so
that the pump pressure . necessary at the highest
altitude would not flood the carburetor or increase
the ·fu el consumption seriously on the ground. In this
case the differential pressure at the carburetor would
fluctuate with changes in altitude and with varying
amounts of supercharging.
However, as it is desirable to use existing car­buretors,
a means has been developed for keeping
the differential pressure constan t. Th·is is the special
supercharger fu el relief valve shown sectionalized i1Y
Figure 22.
This valve consists of an aluminum body i1ito
which is screwed a brass valve seat which comes
between two three-eight hs inch pipe thread openings.
On the lower side of t his seat is a 50-mesh sc reen
which protects the valve seat. Fitting on the seat
is a flat brass valve held to its seat by a bronze ad- ·
justable spring. The unusual feature of this relief
valve is the met allic bellows soldered to the top of t he
flat valve. The inside of this bellows communicates
with the one-fourth inch pipe t hread opening in t he
co ver. The· upper · head of the bellows is a. brass
plate each side of which is a gasket. The cover
contains the adjusting screw packed with cotton
wicking soaked in graphite and castor oil.
This relief valve is mounted in a by-pass line from
the pump outlet line to the main tank. An a ir line
connects the one-fourth inch pipe thread opening with
the supercharger air duct. ·when supercharging,
t herefore, two forces are. acting to hold t he valve down
•'
:?3
to its seat; 011e the spring, the other the supercharger
pressure, which is a lso the carburetor bowl pressure.
The pressure available for supplying the necessary
fuel to the bowl is t herefore due to the spring only.
· It can be seen t hat an ordinary pressure ga uge
would read spring pressure plus supercharger pressure,
and would not be of much use to the pilot, so a s uper­cha
rger fuel pressure gauge a lso has been developed
consisting of the ordinary pressure gauge inclosed
in a casing which is also pipe::! to the supercharger
a ir duct. This gauge reads differential pressu re~that
is, the pressure due to the spring in t he relief valve.
The supercharger fu el system, then, is like t he
typical fu el system shown in Figure 18, with the
exception that the relief valve and pressure gauge a re
changed, and each has an air line connected to them
from the supercharger a ir duct.
When the airplane reaches a ltitudes between 25,000
and 30,000 feet, the vapor pressure of high-test gasoline
is near the boiling point, in spite of the low temperatures
encountered. Sucti on pumps are therefore out of the
question above this a ltitude, as this suction lowers the
pressure on the gasoline the slight additional amount
necessary to cause the boiling. The pump therefore
must be mounted below the fu el tank. This is ac­complished
by means of a flexible drive fitted with an
adapter at each end, one mounting on the engine in
place of the pump, and containing a pair of bevel
gears, the other equipped to mount and drive the
pump. Figure 23 is a photo of a Liberty "12"
equipped with this flexible drive and pump.
3 . VARIATIONS FROM THE TYPICAL S YST EM
A number of variatio ns from the typical fu el system
shown in Figure 18 have been tried, some of whic0h
have a lready been discussed under 1 and 2, preceding.
· a. Removal of overflow indicator.- ln t he combined
a ir pres8ure and gravity system, as used on DH- 4's,
the gravity over flow could not be a llowed to return
to the main tank, but consisted of a one-fourth inch
vent tube which led to the trailing edge on one side
of the cockpi t . This has been used in the typical
system instead of t he method s hown, and has the
advantage of lighter weight, and doing away with t he
unsightly line between t he upper wing and the fuselage.
The disadvantages are (1) that when the gravity tank
overflows, gasoline is forced out of t his vent tube
before the cock can be turned, resulting in loss of fuel,
increased fire hazard, and damage to the airplane from
dripping or spraying gasoline ; and (2) t hat the pilot
can not take off with "Both o n," as some prefer to
do in getting out of a bad fi eld, so t hat, in case of main­system
failure at a critical instant, the gravity tank
will automat ically come into use.
b. Addition of hand pump.-Until proper safeguards
have been taken to · keep da ngerous foreign matter
from flowing into the pump gears, and until long
satisfactory service has proven that t he gear pump
is as reliable as other parts of the power pla nt, such
as a crank s haft, magneto, or water pump, a hand fuel
pump is advisable when long stretches of country
a re flown over which do not provide a safe landing
place. The hand pump should be added by connecting
the intake to the downstream side of the stra iner, and
the outlet to the top of the g ravity tank. The o nly
two types of fuel hand pumps which have had any
use in the Air Service are described herewit h.
(1) Centrifugal hand pump.- This hand pump,
known as the type " B- 1 " hand fuel pump, is a small
pump rotated by a fl exible shaft driven by a crank
geared 14 to 1. It must be located below the bottom
of the main tsnk. The outlet line should run para llel
to the overfl ::nv line within t he g ravity tank to prevent
loss of fuel back to the main tank. This type of pump
F IG. 23.-Flex ible dr ive and pump mounted on Libe.rty "12"
has the di sad vantage of a greatly reduced ·discharge
due to increase of head or dec reas~ of speed. By
operating the crank below a certain speed, t he capacity
is reduced to zero. This speed is rather high when
the discharge head is high". Other disadvantages are
the flexible shaft which adds to the cost of ma intenance,
and the fact. t hat the installation is rather heavy.
The a dvantages of this type of pump are (1) elimi­i1ation
of a suction line, (2) immunity due to absence
of valves . from foreign matter in t he lines, and (3)
flexibility of insta llation. T hese pumps are in pro­duction.
24
(2) "Wobble" or oscillating hand pump.-This pump the band pump replaces the gravity tank of the system
in principle is like · the double-acting plunger pump. shown in Figure 18, and a tee replaces the three-way
The following sketch will illustrate its operation. cock. The hand-pump suction line tees off the main­pump
suction line on the pump side of the strainer.
A single pilot-controlled shut-off cock near the tank
-~ --...._ outlet is all that is necessary. If a level gauge of the
""- boiler-glass type, like that used on the PW-8, is used,
there is slight chance of the pilot running out of fuel
i unknowingly. In case this type of gauge, or one
/ ; equally reliable, can not be used, it is better to have
/ > \ I the supply arranged so that the pilot's attention is
This type has been used to a small extent in two forms
(1) of German construction taken from the Junker
airplane and (2) that made by the Pioneer Instrument
Co. The latter is undergoing modification under
direction of the Engineering Division for use as an
Air Service standard. It is intended to put this into
production, if the service testing is satisfactorily
c.ompleted.
It has . the advantage of having a nearly constant
eapacity through the range of discharge heads com­monly
used, and increase in capacity directly as in­crease
in speed. The oscillating motion in operating
the pump is preferred by most pilots to the circular
crank motion of the centrifugal pump.
A disadvantage is the presence of fom check valves,
although two of them must stick open to cause the
failure of the pump.
This hand pump is connected as described for the
centrifugal pump. The discharge line could be teed
into the pump to three-way cock or the gravity to
three-way cock line. Neither of the last two varia­t
ions have been tested, but of the two the connection
below the three-way cock is probably the better.
c. Exchange of gravity. tank for hand pump.- For the
sake of clean des,ign, or because of insufficient gravity
head, some starting and emergency system other than
a gravity tank is desirable. The Curtiss Racer and ~
the Curtiss Pursuit PW-8 are ·equipped with a hand
pump for starting and emergency. The gear pump
and oscillating hand pump. combination is now in use
on the PW-'8 and has been so satisfactory that it is
contemplated as a standard system. In this system
call~d to the low state of his fuel supply by a starving
engme.
Probably the best way to accomplish this is to have
two tank outlets, one at the bottom and the other a
few inches above the bottom. These ·outlets are con­nected
to a three-way cock, having "Main" and "Re­serve"
positions, and the third cock outlet is connected
to the suction side· of the engine-driven pump. The
lower tank outlet is also connected to the hand pump.
When the fuel level reaches the upper tank outlet, as
evidenced by a missing engin~, the three-way cock is
turned from " Main" to "Reserve." To be abso­lutely
safe, the hand pump may be used while making
the change. To shut off the supply to the carburetor
in landing or in a crash, a shut-off cock is necessary
in the curburetor line.
Another arrangement having some merit is the plac­ing
of the hand pump in the intake line of the gear
pump, with a 'by-pass line around it, entering the car­buretor
line through a three-way cock having three
positions, (1) "Hand pump,'' both pumps open to the
carburetor; · (2) "Run," gear pump open to the car­buretor;
and (3) "Off," gear pump and hand pump
connected together. The hand pump would prime the
pump when starting the engine, regardless of any
traps in the line, which woi.1ld simplify installation in
some cases. There is no e~perience with . this system.
The use of a hand pump which requires continuous
operation, as an airplane emergency system, has not
yet been judged by the pilots of the Air Service.
The only actual case known in which the band pump
has had to be used for emergency is that of Lieutenant
Maitland, who, in the 1922 Pulitzer races had to pump
almost continually for nearly an hour due to stick­ing
open of a check valve in the engine~driven plunger
pump.
VIII. INSTALLATION IN THE AIRPLANE
l. GENERAL
This section of the report is written to aid the man
in charge of installing the gear pump system in the air­plane
and testing it on the ground.
It is assumed that the gear pump is mounted on the
engine. If not, the necessary iniormat.ion may be ob­tained
in Section VI. It is also assumed that the
installation is being put in from drawing showing
correct location of the various parts of the system. If
not, necessary information may be found in Section
VII, which should be carefully read.
Plugs will be found in the pump inlet and outlet.
As these are used to keep the oil in and the dirt out,
while waiting installat ion, t hey should not be removerJ
until necessary.
It will be noticed that on the "C- 5" and "C- 2"
pumps there are three slotted one-eighth inch brass
pipe plugs screwed into openings in the body casting.
As t hese openings are drains, the lowest one of the
three plugs should be removed and a one-fourth inch
tube attached to it by proper fittings. These will
ordinarily be one-fourth inch union nipple, co ne and
nut. This drain line should pass downward through
the bottom cowling either directly, or into a drain
fitting common to other drains. In any event, it
should be possible to distinguish dripping out of thE
pump drain from any other drip, so that it may be
known when the packing nut should be tightened.
Piping the gear pump so that no traps exist in the
intake or discharge lines is a very important and
sometimes the most difficult part of the installation .
The reason for this precaution and t he conditions
under which it is necessary a rc fully discussed on
pa~S. .
The installation of the three-way cock presents two
difficulties which must be avoided. (1) The cock must
be mounted :;i,gainst a level surface. It is easily pos­sible
to causb a leaky cock by distort ing the body
casting. (2) The cock must be m ounted to prevent
side pressure on the stem. A common error is to have
the dogs of the control tube end fit too deeply into the
driving yoke. The control tube should be cut to
such a length that t hese dogs will fi t half-way down
the depth of the yoke slots.
A precaution_ which can not be too strongly empha­sized
is t hat of keeping all dirt out of the fu el li nes.
Dirt large enough to wedge between the gear teeth
and cause the pump shaft to shear off, may either
come through with the gasoline :flow, or come down
from above when t he pump is being primed. The
only known failure of t he gear pump in an actual
in8tallation occurred by bras8 chips and mud falling
clown into the gears from a carelessly installed gravity
tan k.
Every possible source of dirt from the line stra iner
t hrough all the tubing and each fitting to the gravity
tank should be scrupulously inspected, and each line
and fitting installed should be protected from further
dirt .
2 . GP.OUND TESTS
After checking tl1e inst a llation for leak8, a series of
ground tests should be performed to insure t hat the
fuel system is ready for :flight.
a. Pressure gauge .- Oheck t he accuracy of the pres­sure
gauge by turning to "Gravity on." The reading
should be the difference in level between the fuel in
the gravity tank and the pressure gauge in feet
divided by 3t.
b. Prime.- With 1 gallon of gasoline available at
the main tank outlet, start t he engine with three-way
cock at " Gravity on." vVith an engine speed of 600
revolutions per minute, turn t he cock to "Both ·on,"
and 30 seconds later to "Run." The pressure gauge
should · immediately show that the pump ha~ primed.
If the pump does not prime after this treatment
follow directions given on page 26.
c. Reliefvalve.-With the three-way cock at " Run; ' '
and the engine speed about three-fourths full speed,
the pressure gauge should read from 2! to 3! p:mnds.
If it does not, adjust the relief valve to give this pres­sure.
Directions ·for this adjustment are given on
page 16.
d. Gravity tank.-In changing from "Run" to
"Gravity on" at full throttle, and with only a gallon
of fuel available at the gravity tank outlet, the maxi­mum
engine revolutions per minute should be checked
to see that it is correct for the head available.
e. Gear pump capacity.- Obtain the capacity of the
pump by taking the time to fill the gravity tank, the
capacity of which has been found, and adding the
approximate fuel consumption during the run. The
pump capacity should not be less than that shown by
the curves in Figure 9. If it is less, the pump should
be replaced.
.f. Overflow indicator.- After the gravity tank has
overflowed, and the three-way cock turned to " Run,"
the overflow indicator should show clear. If it does
not, there is a trap or obstruction in the overflow line,
or else the relief valve line is so installed that gasoline
backs up the overflow line. It may be due to a leak
in the overflow line within the gravity tank.
g. Packing.- During any of the above runs, no
leakage should have occurred at the pump-packing
drain. If dripping has occurred the pump should be
removed and the packing nut tightened (see p. 26 for
directions).
h. Leuel guage.-See that the level gauge indicates
properly when the tank is full and empty.
i . Hand pump.- If a hand pump is used, obtain its
capacity by the length of time necessary to fill the
gravity tank using a certain number of strokes per
minute. This should be compared with the capacity
data for that type of hand pump.
IX. THE GEAR PUMP IN SERVICE
I. GENERAL
The normal operation of the gear-pump fu el 8ystem
was described on page 22. This ~ection is "written
for the use of the mechanic and pilot in locating
trouble.
Troubles with the gear-pump fu el system, assuming
that the parts have been made properl y and the
grou ud tests were passed successfully, have so far been
entirely due to dirt built into or acquired by the fu el
system.
To understand the following, the reader should have
read Sections VII and VIII.
2. TROUBLE H UNTI NG
a. Engine will not run on gravity.- It is assumed (1)
that the engine will run on the pump, (2) that it i8
known at what speed the engine should run on gravity,
and (3) that this speed is not obtained. The most
likely cause then is dirt obstructing the gravity tank
outlet or line, or the carburetor strainer is choked.
The former can be tested by breaking the connection
~6
at t he carburetur and comparing Lhe fi ow with t he
engine co ns urnpt ion.
b. The gear pump will not prime.-lf it is certain that
the three -way c::Jck has b 3en at t he " B::Jt h on " p osi­tion
for 30 se ~ '.J nd s and t hat the pressure gauge is not
at fa ult, look for a clogged or leaky inta ke line from t he
tank to t he pump or an obstructed tank out let or line
strainer. If t his revea ls nothing, look for a clogged
line between the pump and three-way cock. If the
pump still refuses to prime, it is possible that the
h ousing has been badly scored by foreign matter , that
the pump sha ft has s heared due to the gears becoming
obstru cted, or that the life of' the pump is past . The
life of the pump would ordina rily be not less t han 1,000
hours.
c. Engine will n ot run on pump.- It is assumed that
the engine will run on gra vity. H t he pump is above
the level of fu el in t he main tank, there is only one
reason why t his would occur if t he pump has primed,
and t ha t is the relief valve sticking open. This would
not cause the engine t o quit if the relief valve line dis­charges
suffi ciently high a bove t he carburetor.
If t he pump is below the level of fu el in t he main
t a nk, the trouble may be a clog15ed t a nk outlet, strainer,
or line from tank to pump or from pump to three-way
cock, or the pump shaft may be sheared off due to the
gears becoming obstruct ed .
d. Engine will not run on either gravity or pump.- It
is assumed t hat the trouble is with the fu el system,
and not with the carburet or. There are only four
parts which could cause t his trouble, and which a re
common to both main and grnvity syst ems, viz, the
vent, the three-way cock, the line_ from the three-way
cock to the carburetor, a nd the carburet or strainer.
These should be in vestigated first, and if t he trouble
is not loca ted , it must be one or more of t he t roubles
described under " a" combined wit h one ur more of
those described under " c " .
~. En gine will n ot run on" Both on. "-As~ uming t hat
the engine run s on pump a lone a nd gravity a lone, this
trouble could occur only in case th ere is a vent at the
main tank only (seep. 21).
f. En gine will run on pump, but press ure is too low.­If
t he "pressure ga uge is correct , a nd t he pressure can
not be increa sed to the proper point (see p . 24) by
adjusting the relief valve, the ba ll of the latter is
probably held off its seat by dirt. If not , t here may
be an obstruction in the pump lines, strainer, or tank
out let . Possibly the pump is worn or damaged to
such an extent t ha t the capacity isn't s ufficient.
g. E ngine will not run at idling speeds.-The same
t rouble causing " ! " above could cause the e ngine to
run a t high , but not a t low speeds.
h. Engine will not run above a certain alti tude.- The
same trouble causing " ! " above could cause the
engine to run satisfact orily unt il a certain a lt it ude
was reached. In this case, howe ver, the pressure on
the ground would ordina rily be below the pressure
recommended for t a king off .
i. Pressure is too hi gh.- If t he pressure ga uge is
correct, and t he pressure can not be lowered to the
proper point (see p . 24) by ad justing the relief va lve,
the by-pass line C::Jntaining the latter must be ob­structed.
j . The . gravity tank a ~c'id e ntally emplies .- E xccpt
t hrough leaks in the tank itself or by way of the filler
cap, there are only two possible ways of emptying t he
gravity t a nk, viz, through the overflow line, or through
the out let line. The tank will partially empty by t he
fu el slopping into t he overfiow line. It will ent irely
empty by this means only by a leak a t t he base of
the overflow line within the gravity t a nk. When the
a irplane is not in use, and if the three-way co:::k is
t urned to " Gravity on," the tank may empty through
a leaky needle valve in the carburet::Jr float chamber.
If th e t hree-way C')Ck is a t " Off, " in t he case of
t he " C" type cocks (see p. 17), or " B::Jth on " with
eit her t he " C " or "E" t y pes, the gravity tank will
d ra in through t he pump to t he main tank. If there is
a separa te main t ank vent and the main tank is full ,
it will flow out on the floor, while if there is no separat~
vent, it will climb up the overflow line and show h
the overflow indicator.
k . Packing lealcs .- The pump must be removed .
Referring to Figure 8, remove screw 19, lock plate
assembly 7 and 8, and turn packing nut 6 a full t urn .
Replace pa rts and remoun t pump. If packing still
leaks, repeat until ent ire travel° of packing nut has been
used up. If the leak continues, put in new cork pack­ing
5. This is represented by Engineering Division
d rawing 066325 " Fuel pump gland packing." In put ­ting
in a new packing, the packing nut should be
tightened only s uffi cie ntly to prevent leakage, and not
over two t urns below t he point wher e t be packing nut
is flu sh with t he body casting. If more turns are
necessary , t he packing is fault y and should be replaced.
1. Gasket leaks.- Tighten cover screws if loose. If
cover has been removed , examine ga~k et and remove
a ny fine metal part icles or dirt embedded in its surface.
If r1ecessary to replace gasket, use vellum drawing
paper or i.Joud, eith er .one of which must have a thick­ness
between 0.0025 a nd 0.003.
3 . TROUBLE I N F LIGHT
a. With typical f uel system.- If th e engine st a rts to
miss seriously and the pressure drops, it is necessary to
t urn instantly to "Gravity on " and adviEable to
search for a landing field . In turning to " Gra vity
on " it is essential t hat th e t hrottle be closed to a
position consistent with the available gravity head.
The maximum engine speed p ossible on " gravity"
should be determined before