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Патент USA US2409976

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Oct., 22, 1946.
Filed March 6, 1943
Patented oct. 22, 1946
Russell R. Curtis, Dayton, Ohio, assignorto Curtis.
Pump Company, Dayton, Ohio, a corporation of
Y Ohio
>`lipplimtißn March 6, 1943,*ser'ia1'Nq.-478,213 ,_
`10 Claims.
This invention relates to the maintenance of
selected pump `pressure differentials above se
lected base pressures.
otherside. A spring in thistsecond relief-valve
Will `determine .the pressureadifferential ¿main
tained by »the .pump under emergency dutyper
Specifically the invention relates to the-control
of-fpump discharge pressures'by a ñrstbalanced 5 V'The .system of this „invention ythus providesffor
relief ‘valve assembly ,subjected` to pump .pressure
the maintenance `of 'selected> pump pressure :dif
on one side `and base pressure-.onlthe otherside,
together with Va positively-controlled valve for
subjecting the balanced relief valveassembly to
pump discharge >pressure instead of said base ,
pressure, and a secondrelief valve assembly for
limiting the effect of `pump pressure on said first
ferentials, based on the same or ».diiferent Abase
pressures.` For example, Hthe‘balancing rmeans of
theV pump relief valve can-be subjected -tofa ibase existsvin the fuel tank, -while the
Second `relief Valve can be subjected .to-.1a `base
pressure such as existsin thefueltanhorthe
>relief valve assembly-«whereby the .pump cande
liver fluid under selectedconstant pressuredif
supercharger pressureof >the airplane engine [be
ferentialsi-based on the same Aor .different base
fI-t is, fthen, an object Aof this invention `to ` pro
vide .an ~ assembly ?for „maintaining ,selectedt pres
ing suppliedfby thepump.
.This invention is especially `applicableto air
sure differentials based .on-the sameiorfdifferent
base pressures. , '
craft fuel systems and Iwill lhereinafter `be de
scribed »as 4embodied .in such systems, `although it
`Afurther object `ofthe ',¿inven'tion Lis toprœ
should be understood that the .invention Ais Vnot 20 videa pump assembly having a 4balanced >relief
limited to aircraft usage.
valveiwith a Vrelief» valve` contrölsystem sci_that' the
` ’According «to this invention, a. fuel .pump with
pump can maintain different _selected I'discharge
a balancedrelief 'valvefassemblyismountedrin an
airplane fuel tank to receive‘fuel therefrom rand
deliver the fuel underpressure througnafuel‘line
to >a- secondiuelpump .driven by the» airplaneen
Astill further object of {theinvention .isjto pro
videfan aircraft fuel` system‘capable of ,delivering
a'constantnormal fuel pressure differential above
gine. The ‘fuel pumpin the tank is ,preferably
albasefpressure as Wellas a constant increased
driven by an electric motor.
emergency" fuel pressure .di?ferentialfabove a'íbfase
I‘ The fuelpump S in .the .tankig equipped with: a
spring-urged relief - valve setto .maintain a de~ 30
sired. pressure on `the ,dischargeside of the pump,
inthe order of seven oreighttpoundspersquare
inch. "Such pressures will prevent liberation of
, A still 'further objectief theinvention is .to pro
vide, `in an aircraft `fuel system 'havinga plurality
of fuel pumps in serie‘s’orïìtandem arrangement,
a' relief valvearrangem’ent for at leastone ofs‘aid
gases and vapors",inrïthe’fuelline- In order to
pumps capable ofV automatically maintainingfdif
‘ "
'maintain “a constant-,pressure differential. inthe 35 ferent selected fuelpressures.
VAnotheriobject istoprovidefa positive‘displace- ,
‘discharge side ofjthe fuel' pump, determined
solely bythe springj‘pressure rexerted on-.the relief
ment type booster pump for aV fuel system witha .
relief valve assembly that can `be selectively con
the Arelief valve assembly which is subjected to
trolled‘to maintain a selectedjconstant pressure
pump _pressure `on .one sidel and "basel, pressure on 40 differential on"`the ‘ discharge 'side of ‘ the (booster
the ‘othergside during" normal . operation. The
pump above a selected basejpressure.
valve of'this pump, .a diaphragm‘lis provided in
basei pressure‘is lpreferably that pressure existing
in the' tank in' `Which‘the 'fuel pump is' mounted.
"Under emergency Aconditions, as,.for example,
inïhigh altitudeiñyingyand in case'of damage to
the “engine-‘driven `ifuerpump, it"`is desirable .to
maintain a higher pressure differential on 'thel‘dis
A `still further obj ect’ofY this inventionjis to-‘Lpro
Videg'inian aircraft’ fuel “systemjof the ‘booster
pumpeengine-driven fuel pump type, a'positiv'e
displacement booster pumphaving a balancedre- '
lief valve assembly capable of maintaining anim
creased pressure above Ltank pressure on the irl
take'side ofthe engine-‘driven‘fuel‘pump during
charge-side‘of the pump ?mounted in 'the tank.
normal operation, ‘and >capable ,of 'maintaining a
For this purpose, the ¿discharge sid'e‘of i:the pump
is ïjoined `«with a*positively-controlled valve >such 50 higher .controlled pressure duringr emergency
as ~açsolenoid-ioperated =valve. When this valve Vis
>Other and further-objects ofthe‘invention Will
actuated it >Will‘sulojec't 4"both sides of >the-relief
be apparent to those "skilledfin‘the art from Athe
valve to pump discharge pressures instea‘d‘of‘sub
' jecting - onellside `-`to ’ pump - discharge pressure and
following Vdetailed description pof )the annexed
the/other sidetofbasejpressure-las in‘ normal oper 55 sheetof drawings which, by'wayçof preferred
example Vonly,'illustrate one embodiment of ‘the
ation. 'ßA-‘second relief valve 4is‘also provided‘to
limit‘the pump `-‘discharge pressure---e‘ñî‘ect on the
balancing :means of »the‘ipumplrelief Valve. "This
second? `relief `>valve 4"«is “subjected ïto‘ibase'r'pressure
On‘ the drawing:
Figure 1 ` is ' af ~broken rvertical’` 'cross-sectional
on'loneïside .fand~ pump l discharge pressure 'on »the 60 view of‘an wairplane fuertank‘having mounted
therein apparatus according to this invention
to the relief Valve 26 to move therewith, While
the peripheral portion of the diaphragm can be
and also showing, in side elevation, a portion of
clamped between casing sections, ofthepump.
the aircraftenginereceiving fuel from the tank.
, Figure 2 is a‘wiring diagram forv the appa
ratus shown in Figure 1.
As shown on the drawing:
The bottom of the diaphragm 32' is thus sub
jected toA pressure in the chamber 34, while the
s; = top of the diaphragm 32 is subjected to whatever
In Figure
an 1airplane
the reference
fuel tank
the atmosphere as at Ilia. An lairplane engine II is.
equipped with an >engine-driven fuel` pump I2 for
supplying fuel under pressure through a dis-v
able source of electric current, such as a battery
B. lCurrent to the motor >35 from the battery B
charge line I3 to a fuel and air mixing device
such as a carburetor I4 for the 'engineN II.' The`
carburetor I4 discharges, as is customary, into
the intake manifold I5 of the engine II.
A turbo-supercharger I5 discharges air un
der pressure'through a pipe I'I to the carburetor
I4.` The fuel pump I2' includes a balanced relief-
is controlled by a switch 36.
valveassembly therein (not shown) subjected to
by the pressure of the spring 28, since this spring
urges ,the relief valve 2‘5 to closed position', and
the relief valve, by being subjected to pump dis-V
, the pressure in the intake manifold I5 through 20
aline I 8. Alternatively, of course, the "line -I8
could communicate with the discharge tube I1 of
base pressure exists in the spring chamber 33.
As shown in Figure 2, the pump 2U is driven
by an electric motor35 energized from any suit
the 'supercharger I 6 .
In accordancewith this invention, afpositive
During normal operation, the pump 20 pumps '
excessive Yamounts of fuel into the discharge side
25 thereof, and the reliefvalve 2t is opened to
recirculate the excess fuel back to the intake side
2| of the pump. The pressure maintained in the
discharge side 25 of the pump will ïbe controlled
charge pressure on the other side thereof is, of
course, urged to open position by this discharge
pressure. The diaphragm 32 Ais arranged forfçof
displacement type booster pump 20 is mounted in
the bottom of the fuel tank I0 to receive fuel di
rectly from the tank. The pump 29 has an inlet
the spring chamber 33 balancedrby an equal valve
2| communicating'with the bottom of the tank,
area exposed to pump discharge pres`sure._`> ` In
so that fuel’in the tank will drain directly` into
addition the varea. `of the diaphragm 32 'exposed '
movement with the relief valve and has an effec#
tive area on one side exposed to base pressure jin
the pump Awith a minimum .of restriction. , Y'I‘he 30 to inlet pressurein the chamber 34 and tending
drawing illustrates the inlet 2l to be somewhat
'elevated above the bottom ofthe tank. "It should
'be understood that, in actual installations, the
inlet 2l` will communicate with the very bottom
of the tankandthe elevated position‘of the pump
vto move the relief valve 26 in one direction is
balanced by an equal area on the valve exposed
to the chamber 34 tending to move the valve in
the opposite direction.
The assembly is thus balanced'against variae
20j in V'the ‘tank `,has been lillustratedl merelyV for
tions in inlet pressures and compensating varia‘- i
the -purpose of convenienceinV illustration ofthe
tions in pump discharge and base pressures, so
various tubes in the system.
that the pump pressure'will be maintained at a
pressure differential above the base pressure de-v
„ '
Thev particular pump 29 illustrated is of the
_sliding-vane typeincluding a sleeve 22 defining 40 termined solely by the spring.,
The chamber 33 communicates through a tube ‘
agjpumpbore 22ïd'with its inner surface andre- "
Íceivingtherein a roto-r 23 carrying a plurality of
V3l with the bottom chamber 38a of a second re
sliding Avaries. 24 for `acting on ,theVV pump _bore
22a. to propel fuel from the inlet 2I tothe outlet
25 of',.the pump. _ This >outlet„25 is connected
through ‘a pipe or tube 25a with`the intake side
of the' engine-driven fuel pump I2,v
i .
’I'he discharge >side 25 of the pump 29 is adapt
-ed to‘communicate with the intake side 2IY of
the pump through a relief valve` 26 to relieve eX- I
cess „pump pressuresL The’ intake side 2l of the
pump is connected> to the discharge side 25 of
they pump through a by-pass valve 21 to by-pass
vfuel around 'the >pumping element, in the event
that the pump 'does not supply suiiicient fuel `to ..
the intake of the pump I2.l The by-pass valve
`2.` _held in closed positionby a light spring 21a;
r’The »relief valve 26 is urged to closed position
by means of a coiled spring 28 mounted in a
lief valve assembly 38. This assembly includes an
intermediate chamber 38h separated from the
chamber'38arby a relief valve 39, and a top cham
ber 38e separated from the intermediate 'chamber
38h by a'flexible,'diaphragm` 4III) similar to: the .
diaphragm 32. The relief ,Vall/,e l39 islconn'ected
to the central portion ofthe diaphragmÃIl, and is
spring-urged to closedposition by a Ícoil spring 4L I
in the top chamber 38o. The spring 4 I, similarto
the spring 28, can be radjustably compressed by
means `of an operating screw 42 so as to exert ,a
desired pressure on the relief valve 39 through
thevdiaphragm 40.
The chamber 38h c_ommunicates'with the in
teriolr of the tank II)` through a drain vline 43. l
The chamber '33e communicates ythrough a
tube 44 with either the intake manifold I5 ofithe
airplane engine II or with the ambient air sur
u ’TheV compression of the'spring 28 can be ad
rounding the tank depending upon the position
~justed by means of a control screw 29 which
,operates a top retainer 30 for the spring, to move
of a valve 45, The valve 45 is adaptedr to se
lectively connect the interior of the chamber 38e
this retainertoward and away from a bottom
with either the ambient air or the intake mani
>retainer SI for the spring.
fold. Thus the chamber 38e can either besub
jected to a base pressure, which is the ambient
air pressure, or the engine intake manifold
In order that the pressure of spring 28V wil1 be
the sole, determining factor for the amount of
fluid relieved from the discharge side of the pump,
anpressure-balancing _flexible diaphragm 32 is
provided. Y'Ilhisdiaphragm 32 can be composed of
synthetic rubber-impregnated flexible fabric.
The diaphragm 32' separates a chamber 33 in the
casing housing the spring 28 from a chamber 34
in the pump housing the >reliefvalve 26.
'diaphragm has me central portion thereof. iixed
The tube 31 has a branch »tube 31a communi
eating with the middle compartment 45a of a
positively-operated valve 46; The chamber 46a
has a bottom port 41 joining it with a bottom
chamber 4Gb. A port 48 joins thechamber .46a
with a top chamber 46c. , The chamber 461,);_Comf
municates with the interior of the tank through
a drain> line 49. The chamber 46c-is connected
through-a tube 5l! with the fuel line 25a on the
discharge side of thepump 2B. The tube 50 has
ay restricted- intermediate portion 50a to-preventi
excessive leakage of fuellfrom the line 25a',A into
the compartmentltßc, while at the same time sub
jecting the compartment 46c to the pressure eX
isting in the fuel line 25a.
which comesî into eifect to vent the chamber 331
to the relief ‘valve 39 Whenever the chamber 33v
is not vented tothe tank through the drain line
¿9; The relief valve 39 is adapted to beopened"
Avalve 5l-is provided for closing the portll'l,
anda-.second valvei52 is‘provided for closingïtheport 48. The 'valves 5l.A andf52iare secured on.A or
integral-with a shaft 53 i and îare \ so positioned that i'
the port 4l is closed when’the port lliifisop‘ened`
and, when the port 46: is closed, the; portV 41:1 isA
The shaftv 53í is connected toa solenoid'corecäß"
surrounded by a solenoid coil 55. Asrillustrated,
the» coil 55> is energized.: fromïthe batteryir B? and
a switch` 5l in the battery circuit t0 the coil 55
isclosed so` that, as illustrated> in Figure» l, the
core 5‘4 is in raised positiomto open the port 48:
and `close theqportß'l. A spring ößî urges the; core
by pressures' existing in the chamber 33 abovev
pressures exertedon the relief valve 39 by the
spring 4l and by the pressure in the compart
ment 38o. When opened, the valve 39 Will‘vent
the chamber 33 to the interior of the tank '
through the drain line' 43.
_The spring ä! _can be set to exert any desired
.pressure on the valve 39 and the pressure in the
chamber 38o can either be based on ambient air
pressure surrounding the tank I0, or pressure in
the intake manifold l5 of the engine Il.
Therefore, the pressure in the chamber 33 is lim
itedby a second relief valve mechanism which is
arranged to maintain a desired constant pres
sure differential above a base pressure» (either
ambient air pressure or intake manifold. pres
is,` dea-energized ‘ as, for»A example, .when the switch
sure). Since-the ambient air pressure is sub
stantially the same as that existing in the vented
tank lli, except for a slight Ádifferential due to
head of fuel in the tank, the base pressure‘on
which the pump discharge pressure diiîerential
51 is open as shownpin‘ FigureiZ.
is maintained can be the same, or` different, de:
54. to- move . the valve“ 52 to, closed position,~ and'y
the-.valve 5l toY open position, when the` coil‘liä.
When the solenoidcoil‘. 55 mda-energized', the
chamber 33;' of thepumprZD, isvent‘edto the4 in
terior; of-` theïtank Nl 0 ëthroughthe tube> 3l", branch
31a,_open portA llf'lg.chamberi‘liiîb;` and drain line 4Q) The s base; pressure.: on the balancing mechanism
for.: the: reliefi valvegZB `is thusthat‘ pressure eX
isting; in the, tank> il);A Under such operating- con-
ditions,¢of_l course,.the; port; 48 `is closed and the
chamber33-is not. subjected` to pump discharge -
pressure through'> the tube 5U." Under these cone
ditions, the pumpf willdeliver` fuel atta constant
pressure differentiaL above‘the base pressure ex-`
isting‘infthe'interior'of'the tank depending upon
the-settingof~ the springL 28; The spring 28‘ is
pending upon Whether or not the chamber 38c
is vented to the atmosphere, or to the intake
manifold pressure. In any event, the spring 4|'
will be the sole determining factor for .mainte
nance of the increased pressure differential above
the selected base pressure when the pump 26 is
being used for emergency duty.
From the above description it Will be under~
stood that this invention provides apparatus for
maintaining selected pump pressure differentials
above selected base pressures including a low
pump pressure differential for normalY operation,
and a high pump pressure diiferential for emer
gency operation. During emergency operation
the engine-driven fuel pump l2 may even-be in
operative and the pump 2li will be suiiicient to
25a will be from seven to eight pounds per‘square
supply fuel to the carburetor M tcrrnaintain-oper
inch' above tank pressure:` Such pressures` arei
sufficient to preventï liberation ofi gas andvapor' ' ation of the engine. The pump'` i2 is substan
bubbles in the fuel’line and'only fully liquidïfuel .g tially identical with the pump 23 and includes a`
by~pass means so that fuel from. the line 25a
is‘pressured through thefuelY line 25a to‘ thel in
can be by-passed around the pump into the'tubev
take side of- thev engine-driven fuel* pump- i2.
Failure‘fof the system through vapor l‘ock‘is- thus
If the; pump 2U becomes inoperative the'by-pass
preferably. set so> thatA the fuel? pressure- in line
Under emergencyJ conditions,` however,> suchL as"A f:
when the engine~driven pump` |2‘ fails, it‘ is, de
sirable-to deliver fuel under higherfpressures to:
Unless'some means were provided` '
for changing the> pressure ofi the spring 23v on
the relief~ valve 26, or for -adding to the eiTectof :f
this springy pressure on‘` the ; relief- valve, theÀ di‘s~
valve 2'1 is effective so that the pump I2 can
always receive fuel from the tank.
It will, of course, be understoodY that various
details of construction may be varied through* a
Wide range-»without departing from the principlesV
of this invention and it is, therefore, nottthe‘pur
charge pressure of ' the pump would- remain the
pose to limit the patent granted hereon other'
wise than necessitated by the scope of the ap
pended claims.
In accordance with this inventionthe solenoidv
valve 46 is energized, as by closing the switch til:`
to' open the port 48 and close the portßl'l.` This
vents discharge .pressure from the line 25a,
through the tube 5i)` to the chamber été; and
thencel through. the port 43. intoI the chamber
46a, branch tube 3'la,.and`tube_3-l intothe spring.
chamber 33. As a resultpump discharge.A pres.
sure, isadded to., the spring pressure, in chamber`
33, and the relief valve is urged toward` closed.
positionwith an addediorce thereby` permitting
the, building up. ofpressurein the line 25a.
This pressure would buildup to,the maximum:r
capacityr ofthe pump; or rupture ,point of the
diaphragm 32, unless lsome means were provided
for relieving the pressure. This means is pro
vided in the second relief valve assembly 38 75
I claim as my invention:
`l. Apparatus for maintainingr selected pump
pressure differentials which comprises'a pump
having a ñuid intake and aI fluid discharge' side,
a relief valve for relieving fluid from the discharge
tothe intake sideof- the pump, spring-biased dia
phragin means urging the- valve toward closed
position for maintaining a selected pump dis
charge pressure, a» positively' operated valvefor
selectively subjecting said diaphragm~meansfto
pump discharge pressure to` increase the relief;
valve closing for-.ce` exerted. by‘said means and'
create a» diñerent pump discharge pressure` dife
ferential,> and» a second relief valve'f Cooperating,
with said positively operating valve for limiting
said effect.
2. Apparatus for maintaining selected constant
pressure differentials which comprises a pump
havingan inletY and an outlet, a relief valve as
sembly for relieving fluid from the outlet to the
said valve can be actuated'to move the valve
inlet side of the pump, said assembly including
head for subjecting the spring chamber to tank
discharge pressure, >means for venting the third
chamber in the valve to tank pressure whereby
pressure-balancing means subjected to an ad
pressure or to pump discharge pressure, and a
justable pressure on one side and the pump outlet
pressure on the other side for maintaining `a
second relief valve mechanism operativev forre
lieving excess pump pressures from the spring`
predetermined pressure differential between the
pressure in the pump outlet and said adjustable
pressure, a second valve subjected to pump outlet
pressure on one side and on the other side to
the pump inlet pressure; means for operating'said
second valve to subject said one side of the pres
sure-balancing means to pump outlet pressure,
and a third valve including pressure-balancing
means vented to the pump inlet pressure on one
side and on the other side to said one side of
the pressure-balancing means >of the relief valve
for relieving pressure on said one side of the
pressure-balancing means of the relief valve when
said one side is ventd to pump outlet pressure
whereby said second valve can be operated to
select constant pressure differentials of different
6. Pump’pressure control apparatus compris
ing a pump having a relief valve normally sub
jected to pump discharge pressure _on one side
and a predetermined constant but adjustable
pressure on the other side, and means >for se
lectively adding pump discharge pressure to said
other side of the relief valve to increase the dis
charge pressure to greater than said predeter
mined value.
7. Pump pressure control apparatus compris
ing a pump having a relief valve normally sub
jected to pump pressure on one side and am
bient plus spring pressure on the other side, a
solenoid operated valve for adding pumpdis
charge pressure to said other side of theV relief
valve, and a second relief valve `for relieving eX
3. Apparatus for maintaining selected pressure
cessive pump pressures from said other side of
the first mentioned relief valve.
8. A ñuid pressure control apparatus compris
pressure-balanced relief valve assembly capable
of being set to maintain a constant pressure dif
ing a pump having fluid intake and discharge>
sides, a pressure balanced relief valve for reliev
ferential between the two sides of the valve,
means for selectively subjecting one side or both 30 ing excess pressures from the discharge side ‘of
the pump, said relief valve including an operat
sides of the' pressure-balanced relief valve to pump
ing diaphragm having at one side a pressure`
discharge pressure, and a second relief valve ef
chamber enclosing aV spring for normally biasing
fective to vent one side of the pressure-balanced
said relief valve to closed position, both sides of
relief valve of the pump to a predetermined pres
differentials which comprises a pump having `a
sure whenever said one side of the balanced relief 35 said diaphragm being normally vented `to the-
valve is subjected to pump discharge pressure for
relieving said pump pressure.
4. A fluid pressure control apparatus compris
pressure at the intake side of said pump, a posi
tively operated valve for connecting said pres
sure chamber to the discharge side of said pump
to urge the relief valve toward closed position
and an outlet side, a spring-pressed relief valve 40 with greater force, whereby said relief valve _will
maintain an increased pressure differential' on the
adapted to relieve excess pressures from the dis
discharge side of the pump, and means for reliev
charge to the intake side of said mechanism, a
ing excess pump pressure from said relief >.valve
pressure-balancing device cooperating with said
whenever said positively operated valve effects
valve subjected to discharge pressure on one side
and ambient air pressure on the other side to 45 said increase pressure differential.
9. A fluid pressure control apparatus compris
cooperate _with said spring for maintaining the
ing fluid transfer means having intake and dis
discharge pressure'at a constant pressure olif
charge sides, a spring pressed relief valve for re->
Vferential above the ambient air pressure, a posi
ing a fluid transfer mechanism having an intake
tively-operated valve for subjecting the balancing 50 lieving fluid from the discharge to the intake side
of said fluid discharge means, aV flexible'dia
device to pump discharge pressure instead of
phragm operatively connected to said relief- valve
ambient air pressure, and a relief mechanismand having both the spring opposing` side and
adapted to relieve excess pump pressures on said
the spring aiding side thereof normally exposed
balancing device for maintaining a different con-l
to a base fluid pressure, and means for selec
stant pressure differential above the ambient
pressure on`the discharge side of said mecha 55 tively increasing the fluid pressure on the spring
aiding side of said diaphragm to Vincrease the dis- *_
5; Pumping apparatus comprising a positive
displacement pump having an inlet and an out
charge pressure of Vsaid transfer means.' ` V, Y
10. A fluid pressure control apparatus compris- ,
let, a relief valve for venting the outlet with the
ing a pump having fluid intake and discharge
pump defining a spring chamber, a> flexible dia
phragm separating said chamber from said pump,
fuel from said discharge to said intake side of the
pump, spring means urging said relief valve tov
its closed position, a balancing device connected
inlet to relieve excess pressures, means on said 60 sides, a relief valve in said pump» for release` of '
a spring in said chamber acting on one side of
to said relief valve, both sides ofsaid balancing
said diaphragm, said relief valve acting on the
device being normally vented to the pressure at
other side of said diaphragm, a positively-oper
the intake side o-f said pump, whereby said relief
ated valve having three chambers connected
valve maintains a constant pump' discharge
through ports, a double-acting valve head in said
pressurel differential above intake pressure; and
valve for simultaneously opening one of said
means for selectively subjecting said spring aid
ports Ywhile closing the other of said ports, means
ing side of said balancing device to pump dis
for venting one of said chambers in the valve to
»charge pressure Vfor increasing the pump .dis
pressure in the spring chamber, means for vent
charge pressure differential.
ing an adjacent chamber in the valve to pump
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