US3614269A

US3614269A - Integrated pump-control system using a unitized pump

Info

Publication number: US3614269A
Application number: US17748A
Authority: US
Inventors: Robert S Lanctot
Original assignee: Chandler Evans Inc
Current assignee: Colt Industries Operating Corp; Colt Industries Inc
Priority date: 1970-03-09
Filing date: 1970-03-09
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19
Also published as: GB1336639A; CA927618A

Abstract

An integrated fuel pump and control system has a unitized pump which includes three pumping circuits. A first pump circuit includes a positive displacement gear pump to provide fuel to a gas turbine engine from startup to just below idle. A second pump circuit includes a high-flow centrifugal pump, and a third circuit includes a low-flow centrifugal pump. A pump switching arrangement automatically switches from the first circuit at an engine speed slightly below that of ground idle to either the second or third circuit depending on the engine fuel requirements.

Description

United States Patent [72] Inventor Robert S. Lanctot 2,780,172 2/1957 Coar 417/286 Long Meadow, MESS. 2,812,715 11/1957 Redding et 417/248 [21] Appl. No. 17,748 2,941 ,473 6/1960 Lorenz 417/248 [22] Filed Mar. 9,1970 2,968,348 1/1961 Fortmann. 417/286 [45] Patented Oct. 19, 1971 3,026,929 3/1962 Bums t 417/286 [73] Assignee Chandler Evans Inc. 3,279,522 /1966 Norris et a1. 417/79 west Hartford Conn Primary Examiner-William L. F reeh Attorney-Radford W. Luther [54] INTEGRATED PUMP-CONTROL SYSTEM USING A UNIT [ZED PUMP 26 Claims, 5 Drawing Figs.

[52] US. Cl 417/253,

417/76, 4 7/ 8, 417/427 ABSTRACT: An integrated fuel pump and control system has [5 lnt. a unitized pump which includes three i it A fi t F0413 49/00, F041) 41/06 pump circuit includes a positive displacement gear pump to of Search 79, provide fuel to a gas turbine engine fr stan p t j t b l 426, 427 idle. A second pump circuit includes a high-flow centrifugal pump, and a third circuit includes a low-flow centrifugal References Cited pump. A pump switching arrangement automatically switches UNITED TATE PAT from the first circuit at an engine speed slightly below that of 2,506,611 5/1950 Npal et a1. 417/216 ground idle to either the second or third circuit depending on 2,549,897 4/1951 Everell 417/287 the engine fuel requirements.

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sum w FIG 4 PUMP PXEJSZ/FE INTEGRATED PUMP-CONTROL SYSTEM USING A UN ITIZED PUMP BACKGROUND OF THE INVENTION The invention relates generally to fluid pumping systems. More particularly, this invention pertains to fuel control systems for gas turbine engines.

Fuel controls for gas turbine engines commonly include positive displacement pumps to meet engine startup and lowspeed requirements. Positive displacement pumps are employed to meet these requirements because of their inherent dry lift and high-output pressure capabilities. However, the use of positive displacement pumps throughout the entire range of engine operation presents certain problems, prominent among which are the fuel heating caused by high bypass flows and the ability of the pump to handle contaminated fuel. The unitized fuel pump, shown and described in U.S. Pat. application No. 767,293, filed Oct. 14, 1968, and now U.S. Pat. No. 3,547,557, provides solutions to the problems of fuel heating and contaminated fuel pumping. In order to incorporate the aforementioned pump into a jet engine fuel system, particularly of the afterbuming type, it may be necessary that the pump-fuel control combination be capable of providing pump switching logic to maintain adequate transient fuel-metering accuracy.

SUMMARY OF THE INVENTION The invention provides an integrated pump-control system which possesses the necessary response characteristics to maintain adequate transient fuel-metering accuracy. The invention achieves minimization of the transient disturbance which occurs when the system is switched from one pump to another.

Briefly stated, an integrated pump-fuel control includes a unitized pump having a positive displacement pump and two centrifugal pumps. The positive displacement pump is used for starting and supplies acceleration fuel flow up to an engine speed slightly below that of ground idle. Thereafter, transition to operation on one of the centrifugal pumps occurs automatically. One of these centrifugal pumps is a high-flow unit, and the other is a low-flow unit. At all operational engine speeds from ground idle to maximum, one of these centrifugal pumps provides fuel to the engine. The fuel metering systems for the gas generator and the augmentor operate in parallel off the pump discharge. The pump-control system includes a switching logic arrangement which senses the engine speed, the pressure differential across the control, and the total fuel flow demanded of the control. The flow-metering arrangement is used during all three modes of pump operation. This arrangement precludes discontinuous "switching from one mode of pressure regulation -to another. THis discontinuous switching would otherwise be detrimental to the performance of the fuel control since it would engender large transient fuelmetering errors. Switching from operation on the positive displacement pump to operation on either of the centrifugal pumps is accomplished in such a manner that the fuel-metering systems operate in a continuous fashion.

Accordingly, a primary object of the invention is to provide an integrated pump-control system for gas turbine engines.

Another object is to provide an integrated pump-control system incorporating a unitized pump wherein switching logic is provided for the unitized pump.

Still another object is to provide an integrated pump-control system having a unitized pump wherein means are provided to prevent large transient fuel-metering errors.

A further object is to provide an integrated pump-control system for a gas turbine engine incorporating an afterburner.

A still further object is the provision of an improved unitized pump.

Other objects and advantages of the present invention will be apparent and understood from the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A and 1B are respective portions of a block diagram of an integrated pump-control system embodying the present invention.

FIG. 2 is a schematic view of the unitized fuel pump of FIG. 1A.

FIG. 3 is a schematic view of a gas turbine engine having an afterburner.

FIG. 4 is a graph illustrating the performance of the integrated pump-control system of FIGS. IA and 1B.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT description of preferred embodiment The integrated pump-control system of FIGS. IA and 1B is adapted to supply fuel to either a conventional or afterburning-type jet engine such as that shown in FIG. 3. The engine of FIG. 3 comprises a compressor rotor 10 and a turbine rotor 12 which are mounted to rotate unitarily within an engine casing 14. Compressed air from the rotor I l) passes through combustor 16. The hot gas stream from the combustor I6 drives the rotor 12 and hence compressor 10. An afterbumer 13 is mounted aft of rotor 12 to add additional fuel to the hot gases emerging therefrom for providing additional thrust. The com pressor, rotor and combustor are commonly designated by the term gas generator, and the afterburner 118 is also known as an augmentor.

Referring now to FIG. 2, wherein the unitized pump of FIG. 1A is schematically illustrated, fuel enters an inlet which includes a conduit 20. Assuming that the speed (N,,,) of the gas generator is below that of ground idle, fuel flows from inlet conduit 20 through a conduit 22 to the outlet of a jet pump, generally designated at 24. The jet pump 24 includes a housing 26 having a nozzle 28 mounted at one end thereof within a chamber 30. Nozzle 28 discharges into a venturi section 32 which is joined transversely by an induced flow inlet 34. When the speed of the gas generator is between zero and slightly below that of ground idle (e.g. 55 percent), flow proceeds from conduit 22 into the outlet of the jet pump. Fuel flows away from the jet pump in a conduit 36 and is delivered thence into a conduit 38 via a gear pump unloading valve 40, the details of which are described hereinafter. Fuel flowing in conduit 38 away from the gear pump unloading valve is delivered via conduit 38 to the inlet of a positive displacement gear pump, generally indicated at 42.

Positive displacement gear pump 42 is of the sealing block or wear block type. This type of pump is well known in the art and is shown, for example, in U.S. Pat. Nos. 2,705,259 and 3,208,393. Only the basic elements of the sealing block pump 42 are represented in the schematic diagram of FIG. 2, and it will, of course, be understood that the pump is in a suitable housing 43 and incorporates all of the structure necessary to constitute a sealing block pump as disclosed in the aforementioned patents. Pump 42 includes meshing gears 44 and 46 and a wear or sealing block 48 adapt-ed to engage the gears peripheries, the gears being depicted somewhat in perspective to show the cooperation between the gears and the sealing block 48. The gears 44 and 46 are disposed within their housing 43 in a suitable cavity'or recess 50. The diameter of gear 46 is greater than that of gear 44 for reasons explained hereinafter.

The adjacent arcuate wear surfaces of sealing block 48 are contoured to simultaneously contact the peripheries (tooth tips) of gears 44 and-46. If desired, side plates may be provided for the positive displacement pump to create a region of high fluid pressure in the area of meshing contact between gears 44 and 46. The construction of such side plates is well known to those skilled in the art, and is exemplified in U.S. Pat. No. 3,427,985.

Gears 44 and 46 are mounted on suitable journals (not shown) for rotation, and gear 44 is connected to a shaft 52 which is adapted to be driven by the engine of FIG. 3 by means of a suitable connection to the gear box thereof. Input shaft 52 rotates in the direction indicated by the arrow to drive gear pump 42.

A piston and shaft assembly 54 is mounted for axial sliding movement within a cylinder 56. The left end of the piston and shaft assembly is directly connected tosealing block 48 to urge the same into engaging contact with gears 44 and 46. An axial passage 58 extends completely through the piston and shaft assembly 54 to communicate discharge pressure to the right face of the piston 54 in order to urge the sealing block into firm engagement with the teeth of gears 44 and 46. Sealing block 48 is also urged into peripheral sealing engagement with the teeth of the gears 44 and 46 by a spring 60, disposed within the right end of cylinder 56. Thus, as the pump is started, sealing block 48 is urged into sealing engagement with the gears thereof solely by means of the spring 60. As the discharge pressure from the positive displacement pump increases, due to the increasing speed of rotation of gears, the discharge pressure ported behind the piston 54 supplements the force exerted by the spring 60 to generate a greater force upon sealing block 48. The outlet of positive displacement pump 42 discharges fuel to a first discharge conduit 62. The outlet of first discharge conduit 62 communicates with a chamber 64 in which is positioned a spring-loaded check valve 66 which pennits pressurized fuel to be discharged from the outlet of conduit 62. After a predetermined discharge pressure is attained, the pressurized fuel in chamber 64 is delivered to a main outlet conduit 68 via passage 70, chamber 72 and conduit 74. The right end of conduit 74 is in communication with still another chamber 76. Chambers 72 and 76 function to receive fuel flow from the respective centrifugal pumps as is explained hereinafter. Thus,

chambers

64, 72 and 76, passage 70 and conduit 74 form a discharge manifold for the unitized pump which discharges fluid at a pressure P The pressurized fuel in the main outlet conduit 68 is delivered to the fuel control for eventual metered delivery to the engine.

The above-described fluid flow circuit defined by conduit 22, jet pump 24, conduit 36, gear pump unloading valve 40, conduit 38, conduit 62 and the fuel discharge manifold constitute the first flow circuit which delivers fuel to the engine fuel control at startup and during low-speed operation. The first pumping circuit is then characterized by the dry lift and highpressure capabilities of positive displacement pump 42.

inlet conduit is also connected to an inlet fuel shutoff valve generally designated at 78. inlet fuel shutoff valve 78 includes a generally cylindrical cavity 80, in communication with an inlet port 82 and an outlet port 84, the inlet port 82 being fluidly connected to inlet conduit 20. At each end of the cavity 80 are pressure-sensing

ports

86 and 88 which respectively communicate with boost pressure P that is, the pump inlet pressure, and a signal pressure which is dictated by the speed of the gas generator. Speed signal conduit 90, which embodies an orifice 93, is adapted to direct a preidle speed signal to the inlet fuel shutoff valve 78. A spool 92, having lands 94 and 96, is slideably disposed within cavity 80 for sliding movement therein. The lands 94 and 96 are shaped as cups to reduce the overall system weight. A compression spring 98, mounted in the left portion of the cavity 80, contacts land 94 to urge the spool towards the right to a position in which land 94 covers inlet port 82, this position being illustrated in FIG. 2. The signal pressure from signal conduit 90 is transmitted to land 96 via port 88. Thus, the opposing axial forces acting on the Spool 92 are derived from the boost pressure acting in concert with the spring 98 and the signal pressure acting upon land 96.

Referring again briefly to FIG. 3, an actual speed signal generator 100 is mechanically or electrically connected to the gas generator and generates an output signal E reflecting the speed of the gas generator N, (and hence the speed of the centrifugal pumps). it will be understood, of course, that the actual speed signal generator 100 could be a hydraulic, mechanical or electrical device. The signal E, of the actual speed signal generator is fed to a preidle speed signal generator 102 shown in FIG. 1. The preidle speed signal generator 102 delivers a pressure signal to signal conduit when E, is at a value which is indicative of a predetermined speed slightly below that of ground idle. When land, 96 is exposed to this pressure signal via port 88, the spool 92 is moved to the left, thereby placing inlet port 82 and outlet port 84in fluid communication. Flow emerging from outlet port 84 of inlet fuel shutoff valve 78 is directed to a high-low selector valve 104, this valve serving to direct fuel to either of the centrifugal pumps. The high-low selector valve includes chambers 106 and 108 which are separated by an annular abutment 110. Chamber 106 communicates with inlet port 112 and a highflow outlet port 114 and a low-flow outlet port 116, these outlet ports being respectively connected to the highand lowflow centrifugal pumps. Chamber 108 of the high-low selector valve 104 is in communication with signal ports 118 and 120. The discharge pressure in the main outlet conduit 68 is ducted by suitable means to port 118 of the high-low selector valve, and another signal pressure from the fuel control is ducted t0 the port 120. The signal communicated to port 120 is indicative of the flow demanded of the control, as is more fully explained hereinafter.

Spool 122 is slidingly disposed in the hole defined by the annular abutment 110 for sliding movement therein. Spool 122 comprises a land 123 at the right end thereof which functions as a half area piston and is exposed to the pressure P and the signal pressure from the fuel control. At the other end of spool 122 is secured a disc 124 having an integral axial projection 126, the function of which is described hereinafter. The walls of chamber 106 are provided with

annular valve seats

128 and 130, on which the disc 124 is seatable. When the disc 124 is seated upon seat 130, the flow is directed from inlet port 112 to outlet port 114, which in turn communicates with the highflow pump. Conversely, when the disc 124 is seated upon seat 128, fuel is directed to the low-flow pump from inlet 112 to outlet 116.

The manner of operation of valve 104 is more fully described hereafter. For the purpose of describing the operation of the various flow circuits in the unitized pump of the invention, it is sufficient to state that when low-flow demands are placed on the fuel control, spool 112 occupies a position to the left of that illustrated; whereas, when high-flow demands are imposed upon the fuel control, the valve occupies the illustrated position.

Conduit 132 provides communication between high-flow outlet port 114 and the inlet of a centrifugal inducer impeller pump 134. The discharge from pump 134 is directedvia a conduit 136 to the inlet of centrifugal impeller pump 138. The discharge from impeller pump 138 is directed to the fuel discharge manifold via conduit 140 and a spring-loaded check valve 142 which is mounted in chamber 72. The spring loading on check valve 142 urges it into a position in which it closes off the discharge manifold from conduit 140. it will be noted that check valve 66 performs a similar function. It will also be noted that the back sides of the

check valves

66 and 142 are exposed to discharge pressure in the manifold, the discharge pressure assisting and urging the check valves to their closed positions.

The inducer impeller 134 of pump 138 is drivingly connected by a shaft 144 to a gear 146 which functions as the input drive to inducer pump 134. Gear 146 meshes with gear 46 of the positive displacement pump 42 and has a larger diameter than gear 46 which, as noted heretofore, is larger than gear 44. Tl-lus, the gears 44 and 46 not only serve as a gear pump, but also serve as a part of a gear drive train in association with gear 146, the gear 46 acting as an idler gear in the gear train. Shaft 148 drives impeller pump 138 by virtue of its being an extension of shaft 52. Thus, rotation of shaft 52 simultaneously drives the positive displacement pump 42 and impeller pump 138.

A second flow circuit is that defined by outlet 84, inlet 112, chamber 106, outlet 114, conduit 132, inducer pump 134, conduit 136, impeller pump 138 and conduit 140. The second flow circuit is inactive upon engine startup in the sense that it is not delivering fuel during this period to the discharge manifold. This inactivity of the second circuit is due to the c1osure of the inlet port 32 of the inlet fuel shutoff valve 7%. The second circuit remains inactive until spool 92 is shifted to the left by a pressure signal from conduit 90 and, as previously mentioned, this signal is delivered when the engine reaches a speed slightly below that of ground idle.

It will be noted that while the second circuit will normally be active after the inlet port 32 of the inlet fuel shutoff valve 78 is initially opened, this will not be the case if the high-low selector valve spool 122 is positioned to the left of the illustrated position in response to the fuel control signal which reflects a low-flow demand upon the fuel control system. In this position, the second circuit is blocked due to the seating of disc 126 on seat 128. In this case, the third pumping circuit is activated. As noted above, the selection of the second or third pumping circuit is dependent on the total fuel flow demanded of the fuel control, that is, the sum of the fuel flow to the augmentor W and the fuel flow to the gas generator W Signals, reflecting the fuel flow demanded by the gas generator and the augmentor, are fed to a summing device 150 which produces a resultant signal reflecting the total demanded fuel flow (i.e., the total fuel flow to the engine). The latter signal is directed to a pump selector signal generator 152 which is adapted to deliver a high-pressure signal to the high-low pump selector valve when the demanded fuel flow is below a predetermined level. The pump selector signal generator 152 has sufficient hysteresis so that operation is stable and frequent switching is avoided.

Assuming that the pump selector signal generator has requested operation on the low-flow pump, the high-low selector valve is positioned to port inlet fuel to the low-flow pump.

In this position, disc 124 is seated against seat 128. This, of

course, results from the high pressure communicated to the back of piston 123 via port 120. Thus, when the third pumping circuit is activated due to a leftward displacement of spool 122, flow proceeds from the inlet fuel shutoff valve port 84 to inlet port ll 12 of the high-low selector valve 104 and thence to outlet port 1116.

A conduit 15d connects outlet port lll6 with a vapor core pump 158 which includes an axial inducer 1160 and an impeller 162. Impeller T62 is mounted on an extension of shaft 148 and is thus driven by input shaft 52. The vapor core pump also includes a peripheral slotted window-type vapor core valve 164!- surrounding the eye of the axial inducer. The position of the vapor core valve 164 is controlled by movement of a link 165, which in turn is controlled by a low-flow pump controller i168, which is discussed hereinafter. The construction and operation of vapor core pumps and valves are described in great detail in the following US. Pat. Nos. 3,265,000; 3,142,255; 3,128,822; and 3,106,165. issued to S. R. Tyler. Reference is hereby made to these patents for a more detailed discussion of vapor core pumps and valves.

It will be noted that the actual speed signal generator 1100 senses the speed of both centrifugal pumps, as this speed is proportional to the speed of the engines due to their driving connection to the gear box thereof. if desired, the actual speed signal generator could be connected directly to shaft 52 and 1% since its primary function, with respect to the instant invention, is to sense the speed of the centrifugal pumps. This arrangement insures that an input flow will not be directed to either of the centrifugal pumps until they reach respective predetermined speeds.

The discharge from impeller 162 is delivered, via a conduit 170, to a checlt valve 172 which is similar in construction to the check valves 66 and M2. Flow then proceeds into the discharge manifold from the outlet of conduit 1170 via check valve 172.

In order to insure that either the second or third pumping circuit is vented when it is deactivated by displacement of the high-low selector valve, a vent valve, generally designated at 174, is provided to vent the nonselected circuit. Vent valve ll'ld includes a chamber having inlet ports 176 and 1170, and an outlet port 1100. The inlet ports 1176 and 1178, are in respective fluid communication with conduits M0 and of the second and third pumping circuits respectively. A spool H02, having lands 1% and 1186, is mounted within the chamber of vent valve 1174 for axial sliding movement: therein. Connected to the left side of land 1176 is a flanged structure m0 which is urged towards the right by a compression spring 100. The flanged structure 100 limits the rightward travel of spool 1102, as it is adapted to contact the housing "thereof. Spool 1102 is an axial alignment with projection H26 of the high-low selector valve 1041. When the high-low selector valve is moved to the left of the position illustrated, projection 1126 contacts land 1186 and displaces spool 1102 to the left against the urging of spring 1.90. it will be observed that in the position shown, inlet port 1170 is in communication with outlet port 100, thereby venting the third pumping circuit. However, when the second pumping circuit is deactivated, by virtue of the seating of disc 124 of the high-low selector valve against seat 120, projection l26 positions the spool so as to discontinue the fluid communication between ports 1170 and establish fluid communication between

ports

176 and 100. Thus, the pump positioned in the deactivated circuit is vented. Outlet port 180 of the vent valve 1174 is connected to a conduit 100 which communicates with chamber 50.

A bypass pressure regulator valve 192 maintains a constant differential pressure across the fuel control (e.g., 100 p.s.i.). Regulator valve l92 comprises a housing having an elongated cavity therein. Cavity 1% has an inlet port 196 and an outlet port 198. The cavity 11% is also formed with an annular portion 200. Pressure-sensing

ports

202 and 204! are disposed at the respective ends of the cavity 104 to transmit the pressure across the control to a spool 206, slideably mounted within the cavity. Spool 206 comprises a lower land 200 and an upper land 2110, the outboard face of land 200 being exposed to the fuel controls discharge pressure P,, and the outboard face of land 2l0 being exposed to the controls inlet pressure and the outboard face of land 210 being exposed to the controls inlet pressure P,. A compression spring 212 is disposed in the lower part of the cavity 194 in contact with spool 208. Conduits 21l4l and 216 respectively communicate with the pressures I? and l, to transmit these pressures to the pressure-sensing

ports

202 and 204.

When the spool 206 is in its upper limit of travel, inlet port 196 is blocked by land 208, thereby preventing a bypass flow through the valve to conduit 36. When the spool 206 is disposed in positions lower than that of its upper limit of travel, at least partial communication is established between inlet port 1196 and outlet port 198, and hence some fuel is bypassed during operation of the positive displacement pump. As previously mentioned, the regulator valve is designed to maintain a predetermined pressure drop across the fuel control. Therefore, assuming that the positive displacement pump is in operation -that is, the first pumping circuit -and that the valve is in the illustrated position, an increase in the pressure differential (P -P produces a downward movement of spool 206, thereby increasing the amount of bypass flow. Should the pressure differential decrease, spool 206 will move upwardly, thereby decreasing the amount of bypass flow.

A conduit 220 is fluidly connected to conduit 62 at a loca tion intermediate the discharge of the positive displacement pump and check valve 66, conduit 220 being connected to inlet port 196 of the regulator valve. Therefore, during operation of the positive displacement pump, bypass flow is adapted to proceed from conduit 62 to outlet port 1190 via conduit 220 and inlet port l96. The bypassed flow emerging from outlet port 190 joins with the input flow from the jet pump 24$ and flows via conduit 36 to the gear pump unloading valve 40 and thence to the inlet of the positive displacement pump via conduit 30. The differential pressure (P -P maintained by the regulator valve 192, is not sufficient to actuate the gear pump unloading valve 40, and therefore, this valve does not interfere with the bypass flow proceeding therethrough to the inlet side of the positive displacement pump 42. A bypass circuit is then formed by conduit 220, regulator valve 192, conduit 36, unloading valve 40 and conduit 38.

Gear pump unloading valve 40 comprises a spool 222, which includes lands 224. and 226, mounted in cylindrical cavity 228. Pressure-sensing

ports

230 and 232 communicate with the cavity 228 to respectively direct the pressures P and P, to the outboard faces of

lands

226 and 224. Valve 40 further includes outlet ports 234 and 236 and inlet port 238, as well as a discharge pressure transmittal port 240 disposed in the lower portion thereof.

Outlet port 234 is adapted to communicate with port 230, which is placed in communication with the fuel control inlet pressure P when spool 222 is downwardly displaced. In order to produce such a displacement, it is necessary to create a predetermined pressure differential (P, --P:) which is significantly greater than the differential maintained by the regulator valve 192. Outlet port 236 is in communication with inlet port 238 during operation of the first pumping circuit, as the differential pressure maintained by the regulator valve is not sufficient to downwardly displace spool 222. The discharge pressure transmittal port 240 is in constant communication with the fuel control discharge pressure P irrespective of the position of the gear pump unloading valve, this port serving to transmit fuel control discharge pressure to the outboard face of land 208 of the regulator valve via conduit 214.

When a signal from the preidle speed signal generator 102 actuates the inlet fuel shutoff valve 78 such that a flow commences in either the second or third pumping circuits, the

pressure difi'erential (Pr-P rises rapidly from the differential pressure maintained by regulator valve 192 to a differential pressure which may be of the order of 150 p.s.i. This pressure differential is sufficient to downwardly displace spool 222, thereby uncovering port 234 and covering port 238. This results in a flow from port 230 to the nozzle 28 of the jet pump 24 via port 234 and conduit 242. This differential pressure occasioned by the operation of the second or third pumping circuits is also sufficient to downwardly displace spool 206, of the regulator valve 192, to its lower limit of travel, thereby establishing untrammelled communication between port 196 and port 198. With the port 238 blocked by land 226, input flow cannot reach the inlet of the positive displacement pump.

It will be recalled that the piston 54, which actuates the wear block 48 of the positive displacement pump 42, urges the wear block against the teeth of gears 44 and 46 in response to the force exerted thereon by spring 60 and the pressure ported behind the right face of the piston 54 via passage 58. A conduit 242, which interconnects the port 234 of the gear pump unloading valve and the nozzle 28 of the jet pump 24, comprises a branch conduit 244 which communicates with the left portion of cylinder 56. This connection enables the pressure in conduit 242 to be ported to the left face of the piston 54 to move the wear block 48 away from the gear teeth and thereby unload gear pump. Thus, the downward displacement of the spool 222 of the gear pump unloading valve not only cuts off fuel flow to the positive displacement pump, but also causes the wear block to move away from the gear teeth by virtue of the pressure ported from conduit 242.

During operation of the second or third pumping circuits, the jet pump 24 is in operation. Fuel flowing from inlet port 230 of the gear pump unloading valve is communicated to the nozzle 28 via port 234 and conduit 242. Nozzle 28 of the jet pump 24 discharges into venturi section 32, thereby creating a low pressure at the inlet 34 of the jet pump which induces a flow in the bypass conduit 220 to drain the formerly flooded gear cavity 50. Therefore, during operation of either the second or third pumping circuits, fuel is withdrawn from cavity 50, via conduit 220, port 196, port 198 and conduit 36, to the inlet 34 of the jet pump. Flow then proceeds from the outlet of the jet jump to conduit 22 and rejoins the input flow in conduit 20. It will be noted that the jet pump is in constant operation during fuel flow in either the second or third pumping circuit.

As noted above, vent valve 174 assures that the deactivated centrifugal pumping circuit is vented during operation of the other centrifugal pumping circuit. When the second pumping circuit is in operatiomthe high-low selector valve 104 and the vent valve 174 are in the illustrated positions, and therefore the low-flow vapor core pump 158 is vented to the chamber 50 of the positive displacement pump via conduit 170, ports 178 and 180 and conduit 190. As the jet pump 24 is in continuous operation during operation of either the second or third pumping circuit, the chamber 50 is continuously vented.

When the third pumping circuit is activated, due to the shifting of spool 122 to the left, projection 126 contacts land 186 of spool 182 to thereby shift spool 182 to the left. Leftward motion of the spool 182 results in the uncovering of port 176 of vent valve 174, thereby establishing communication between

ports

176 and 180. Centrifugal pump 138 is thereby vented via port 176,180 and conduit 190.

it will be noted that with respect to the low-flow vapor core pump and the high-flow pump, this venting is mutually exclusive. The venting of the second and third pumping circuits through chamber 50 tends to eliminate windmilling losses which might otherwise be encountered in the inactive pumping circuit.

By way of general comment, the principal flow paths through the first, second and third pumping circuits are indicated in FIG. 2 by the solid arrows, dashed headed arrows and phantom arrows respectively. Furthermore, it will be understood that the check valves in each of the pumping circuits are closed when the particular pumping circuit is inactive, and opened when the particular pumping circuit is active. When a switch is made from the first flow circuit to the second flow circuit, the pressure rises rapidly in conduit 140 to a value which is sufficient to open check valve 142. The subsequently increased pressure in the discharge manifold effects a closing of check valve 66. When a switch is made from the second flow circuit to the third flow circuit, or vice versa, the pressure upstream of the previously opened check valve drops so that the previously opened check valve moves to a closed position. include Referring again to FIGS. 1A and 18, it can be seen that conduit 68 bifurcates to direct the fuel flow from the pump into parallel

fuel metering lines

250 and 252, the

lines

250 and 252 respectively supplying fuel to the gas generator and the augmentor. Line 250 includes a gas generator fuel-metering valve 254 which meters the fuel flowing therethrough. Line 252 also includes a metering valve 256 which meters fuel flow to the augmentor.

Lines

250 and 252 include respective

differential pressure regulators

258 and 260. These in-line regulators are preferably of the proportional plus integral type which permit fast response in the proportional mode to minimize the total quantity of fuel metered in error during the transient. The differential pressure regulators are adapted to maintain a constant pressure differential across the respective fuel-metering valves so that the fuel flow in each of the lines is purely a function of the area of the metering orifice of the valve associated with the line. At the ends of the

lines

250 and 252,

shutoff valves

262 and 264 are provided to respectively shut off fuel flow to the gas generator and augmentor.

The metering system per se is conventional and has been used successfully in numerous jet engine fuel systems. Because of the pressure-flow characteristic of a centrifugal pump (variation in fuel flow rate has only a minor influence on discharge pressure), the operation of the two metering systems in parallel off of a noninlet throttled centrifugal pump causes no dynamic difficulty.

Pressure-sensing

lines

266 and 268 respectively communicate with the

lines

250 and 252 intermediate the metering and shutoff valves thereof. These pressures, which are respectively denoted P and P are directed to a select highest valve 270 which directs the largest of the pressures P, and P to the low-flow pump controller 168, regulator valve 192, and gear pump unloading valve 40, the highest pressure being denoted P 9- OPERATION Start and Acceleration to Idle Referring to FIGS. llA, BB and 2, with particular emphasis on FIGS. IA and EB, it will be observed that starting and acceleration to idle are fully automatic. As the gas generator spool speed increases, the input flow in conduit 20 enters conduit 22 and proceeds therefrom to the inlet of positive displacement pump 42 via jet pump 24, conduit 36, gear pump unloading valve 40 and conduit 39. During this phase of operation, inlet port 82, of the inlet fuel shutoff valve 78, is blocked by land 94, thereby preventing fuel flow to either of the centrifugal pumps. Fuel then passes from the outlet of the positive displacement pump 42 through conduit 62 into the discharge manifold. When the discharge pressure is sufficient to overcome the spring preload on check valve 66, fuel from the discharge manifold proceeds to the fuel control via conduit 68. As the discharge pressure at the outlet of the positive displacement pump increases, the sealing force exerted on the gears 44 and 46 correspondingly increases due to the discharge pressure being ported behind the piston 54 via passage 58. Fuel flows from conduit 68 into fuel line 250 as there usually will be no initial fuel flow in conduit 252, since augmentor operation is normally not required below l/percent engine speed. Therefore, shutoff valve 264 will be closed until this speed is attained. Fuel thence passes through differential pressure regulator 253 and gas generator fuel metering valve 254, the differential pressure thereacross being maintained essentially constant by regulator 2%. Flow emerges from the metering valve 254 and proceeds to the engine via shutoff valve 262.

The pressure at the inlet to the fuel control P and the pressure P in the line 250, intermediate fuel-metering valve 264 and shutoff valve 262, are transmitted to the regulator valve 192 and the gear pump unloading valve 40, the pressure P, being directed thereto via select highest valve 270. When the differential pressure across the fuel control (PfPg) attains a predetermined value (e.g., I00 p.s.i.), regulator valve 192 commences to function to maintain this differential pressure. Fuel is now bypassed via conduit 62, conduit 220, regulator valve 192, conduit 36 gear pump unloading valve 40 and conduit 38. As noted above, the gear pump unloading valve is in the illustrated position during this mode of operation, and therefore the bypass flow is not impeded thereby.

When the engine of FIG. 3 reaches a speed slightly below that of ground idle, the signal E,,, from the actual speed signal generator, actuates the preidle speed signal generator 102, which results in a pressure signal being directed to inlet fuel shutoff valve 78 via conduit 90. Under the influence of the high pressure in chamber 80 occasioned by this pressure signal, the spool 92 is shifted to the left of the illustrated position of FIG. 2 thereby establishing fluid communication between

ports

62 and 84 of inlet fuel shutoff valve '78. The shifting of valve 92 may be considered the prelude to the deactivation of the first pumping circuit and the activation of either the second or third pumping circuit.

Operation on the High Flow Pump If the engine is started at a low altitude, in all probability operation on the high-flow pump will be initiated when the engine reaches a speed slightly below that of ground idle. In the event that the engine is started at a high altitude, operation on the low-flow pump will likely follow the deactivation of the first pumping circuit. It will be noted that the controlling factor in the selection of either the second pumping circuit or third pumping circuit is the fuel flow demanded by the engine.

Therefore, assuming the sum of the fuel flow requested of the gas generator circuit W and the fuel flow requested of the augmentor circuit W is a requested total fuel flow W which is not of a magnitude to direct the pump selector signal generator to deliver a high-pressure signal to port 1120 of the high-low selector valve, the spool 222 thereof will be in the il lustrated position in FIG. 2 when spool 92 of the inlet fuel shutoff valve Ill shifts to the left. 'In this mode of operation, fuel from inlet conduit simultaneously flows through both the llllll first pumping circuit and the second pumping circuit. Flow then proceeds in the second pumping circuit from inlet port 82 to outlet port 84, from where it enters the inlet port 112 of the high-low selector valve 104. Fuel from the high-low selec' tor valve emerges at outlet port 114 and passes through conduit I132 to inducer 34, from where it is delivered to the highflow centrifugal pump R36 via conduit 1136. Flow emerging from the centrifugal pump I38 proceeds to the discharge manifold via conduit 140 when the pressure therein is suffcient to overcome the spring and pressure load of check valve 142.

As the differential pressure (P -P increases due to the flow in the second pumping circuit, the respective spools of the regulator valve and the gear pumping unloading valve are displaced in a downward manner, thereby providing an unobstructed bypass flow path through the regulator valve and blocking the flow of inlet fuel to the inlet of the positive displacement pump 42. Displacement of spool 222 of the gear pump unloading valve produces a communication between port 230 and port 234 which results in a flow through conduit 242 to the nozzle 28 of the jet pump 24. The pressure in conduit 242 (I5) is communicated to the left-hand portion of chamber 56 of the positive displacement pump, thereby displacing the piston, and hence the wear block 43, to the right. The rightward displacement of the wear block 48 serves to reduce the pressure at the outlet of positive displacement pump 42. Therefore, the sequential action of the gear pump unloading valve and the wear block 48 occasions an unloading of the positive displacement pump 42.

The jet pump is now in operation since the unloading of the positive displacement pump 42 initiates operation of the jet pump 24, and thus the cavity 50 is vented via the outlet of the positive displacement pump conduit 62, conduit 220, port 1196, port 193 and conduit 36. The suction created by the flow through nozzle 28 of the jet pump 24 provides the pressure differential for the flow in this flow path. The low-flow vapor core pump 158 is vented during operation of the second pumping circuit via conduit 170, ports 1178 and 1180 and conduit 190, the vent flow proceeding into cavity 50, from where it proceeds to the jet pump via above-described route. Flow from the jet pump enters conduit 22 and is thence delivered to inlet conduit 20 where it rejoins the input flow. It will be that during the switching operation from the first pumping circuit to the second pumping circuit, the flow in

conduits

22 and 36 is reversed.

Operation in the high-flow pump mode (second pumping circuit) is the basic system and does not require a pump control loop. The high-flow pump provides an essentially constant pressure source of fuel to both the gas generator and augmentor fuel-metering system. As shown in FIG. 4, high-flow pump pressure is always at least p.s.i. above the engine back pressure.

During operation of the second pumping circuit, the augmentor may be utilized to provide additional thrust by opening shutoff valve 264. In this case, flow discharged from the discharge manifold of the unitized pump enters

conduits

250 and 252 and passes through the respective pressure regulators, metering valves and shutoff valves. The parallel flows of fuel emerging from the

shutoff valves

262 and 264 are respectively directed to the gas generator and the augmentor.

Switching to operation on either the low-flow pump'with inlet throttling or the positive displacement pump is accomplished such that the respective fuel-metering systems, for the gas generator and the augmentor, operate in a continuous fashion. At most, only an inlet pressure disturbance will be encountered during switching.

Operation on the Low-Flow Pump The total amount of gas generator plus augmentor fuel metered to the engine is computed in the fuel control by summer 150. Should the total fuel signal from the summer to the pump selector signal generator correspond to a predetermined lowflow, pump selector signal generator 1152 will, upon receipt of the signal, direct a high-pressure signal to the high-low selector valve 104 via port 120 thereof. The pressure communicated to the right face of piston 123 by the pump selector signal generator is sufficient to displace spool 122 in a leftward direction into seating engagement with seat 128.

As noted heretofore, during leftward movement of spool 122, projection 126 displaces spool 182 of vent valve 174 to the left, thereby covering port 178 and uncovering port 176. This movement of spool 182 results in a discontinuation of the venting of low-flow pump 158 and an initiation of the venting of high-flow pump 138, the high-flow. pump being vented via conduit 140, port 176, port 180 and conduit 190. After the disc 124 of the high-low selector valve is seated on seat 128, flow through the second pumping circuit is curtailed and flow communication is established between

ports

112 and 116, thereby allowing flow to proceed to the inlet of the low-flow vapor core pump 158, this flow proceeding via conduit 154. The discharge from the low-flow pump 158 is directed to the discharge manifold via conduit 170 when the pressure therein is sufficient to overcome the spring preload of check valve 172. As mentioned above, the pump selector signal generator 152 has sufficient hysteresis so that operation is stable and frequent switching is avoided.

The low-flow pump controller 168 senses the pressures P and accordingly positions inlet throttling valve 164 of lowflow pump 158. OPeration on the low-flow pump is similar to operation on the positive displacement pump to the extent that the gross pressure differential (P -P across the fuel-metering system is regulated. During operation of the third pumping circuit, this differential pressure is maintained at a higher value than that which was maintained during operation of the positive displacement pump. For purposes of illustration, assume that the differential pressure maintained across the fuel control by the low-flow pump controller is 150 psi. Thus, the low-flow pump controller 168 continuously positions the inlet throttling valve 164 of the low-flow pump 158 during operation of the third pumping circuit to maintain a predetermined pressure differential across the fuel control.

It should be noted that when operating in the augmentation mode during operation of the third pumping circuit, the control system automatically selects the higher of the two metered pressures P, and P downstream of the gas generator and augmentor metering valves, and that during operation of the third pumping circuit, the low-flow pump controller 168 regulates fuel control inlet pressure P to be a predetermined amount l50p.s.i.) above the highest of the two metered pressures. Therefore, the metering system operating at the lower metering valve discharge pressure operates with a greater pressure drop across its metering head regulaton' Pump-Control System Perfonnance Turning now to FIG. 4 a pressure versus total fuel flow chart shows the characteristics of a typical pump-control system constructed in accordance with the teachings herein. As the curve representing the discharge pressure envelope of the fuel control show, the discharge pressure P decreases as the fuel flow required by the engine decreases, the shape of this curve being determined by the particular back pressure characteristics of the engine sought to be controlled. When the requested fuel flow reaches s a predetermined value, the third pumping circuit is activated, as previously described, and therefore there fuel control inlet pressure P decreases with the decreasing fuel flow requirements such that P, is maintained equal to P plus a constant differential pressure (150 p.s.i.). Maintenance of this differential pressure is, of course, due to modulation of the inlet valve by the low-flow pump controller. The low-flow pump inlet pressure curve portrays the relationship between the requested fuel flow and inlet pressure when the inlet throttling valve 164 provides a maximum inlet area. The pressure decreases due to inlet throttling for a given fuel flow is easily ascertained at any operating point. For a sample case, FIG. 4 shows, on the low-flow pump pressure versus flow curve, the operating point after the inlet has been throttle to an area A the point being circled. The pump inlet throttling valve reduces the pressure rise across the pump, thereby reducing the pump input horsepower and minimizing fuel temperature rise.

It is to be understood that the particular embodiment of the invention as described above and shown in the accompanying drawings, is merely illustrative of and not restrictive on the broad invention, and that various changes in design structure and arrangement may be made without departing from the spirit and scope of the appended claims.

I claim:

1. In a device for controlling the flow of a fluid a fluid-consuming load, the combination comprising:

a unitized pump having two pumping circuits for delivering fluid to the load;

a low-flow centrifugal pump positioned in the other of the circuits to pump the fluid therethrough; high-flow centrifugal pump positioned in one of the circuits to pump the fluid therethrough;

a positionable selector operatively connected to both of the circuits for directing an input flow of the fluid to either the one or the other circuit;

a pump selector signal generator operatively connected to the selector to generate a signal thereto for the positioning thereof; and

means responsive to the total fluid flow delivered to the load to control the signal generator.

2. The combination, as defined in claim 1 wherein the unitized pump further comprises:

an additional pumping circuit;

a positive displacement pump positioned in the additional pumping circuit to pump the fluid therethrough; and

a shutoff off valve disposed in fluid communication with the inlet of the pump and operatively connected to the first mentioned two pumping circuits for preventing an input flow thereto until at least one of the centrifugal pumps attains a predetermined speed, the shutofl" valve being remotely located from the additional pumping circuit so as not to impede an input flow thereto.

3. The combination, as defined in claim 2, further including:

means responsive to the speed of at least one of the centrifugal pumps to generate a speed signal to the shutofi valve for opening the shutoff valve.

4. In a device for controlling the flow of a fluid-consuming load, the combination comprising:

a unitized pump having an inlet conduit, an outlet conduit, a first pumping circuit and a second pumping circuit, the pumping circuits each being in fluid communication with the inlet and outlet conduits and being adapted to deliver the fluid to the load;

a positive displacement pump positioned in the first pumping circuit to pump the fluid therethrough;

a centrifugal pump positioned in the second pumping circuit to pump the fluid therethrough;

a metering system fluidly connected to the outlet conduit of the utilized pump for metering a flow of fluid to the load;

a shutoff valve fluidly connected to the inlet conduit and the second circuit for preventing a flow of the fluid from the inlet conduit to the second circuit; and

means to sense the speed of the centrifugal pump and generate a signal to open the shutoff valve when the centrifugal pump attains a predetermined speed.

5. The combination, as defined in claim 4, wherein the unitized pump includes:

means to maintain a constant pressure differential across the metering system during operation of the positive displacement pump.

6. The combination, as defined in claim 4, wherein the unitized pump includes:

a third pumping circuit;

a low-flow centrifugal pump positioned in the third pumping circuit to pump the fluid therethrough from the inlet conduit to the outlet conduit; and

a positionable selector operatively connected to both the second and third pumping circuits for directing an input flow in the inlet conduit to either the second or third pumping circuit.

7. The combination, as defined in claim 6, further including:

means responsive to the flow in the metering system to control the position of the selector.

8. The combination, as defined in claim 6, wherein the unitized pump includes:

means to maintain a constant pressure differential across the metering system when the low-flow pump is in operation.

9. In an afterburning-type pump-control system for delivering fuel to an engine, the combination comprising:

a unitized pump having an inlet, an outlet and two pumping circuits adapted to respectively communicate with both the inlet and the outlet;

a high-flow centrifugal pump positioned in one of the circuits to pump the fuel therethrough;

a low-flow centrifugal pump positioned in the other of the circuits to pump the fuel therethrough;

a positionable selector operatively connected to both of the circuits for directing an input fuel flow from the inlet to either the one or the other circuits;

two fuel lines fluidly connected to the outlet for receiving a flow of fuel therefrom;

two metering devices respectively connected to the lines for metering fuel flows therethrough;

means responsive to the total fuel flow in the lines to control the signal generator.

it). The combination, as defined in claim 9, wherein the unitized pump further comprises:

an additional pumping circuit adapted to communicate with the inlet and the outlet;

a positive displacement pump positioned in the additional pumping circuit to pump the fuel therethrough; and

a shutoff valve disposed in fluid communication with the inlet of the unitized pump and operatively connected to the first mentioned two pumping circuits for preventing an input fuel flow thereto until the engine attains a predetermined speed, the shutoff valve being remotely located from the additional pumping circuit so as not to impede an input flow thereto.

ill. The combination, as defined in claim it), further includmeans responsive to the speed of the engine to generate a speed signal to the shutoff valve for opening the shutoff valve.

12. In an afterburning-type pump-control system for delivering fuel to an engine, the combination comprising:

a unitized pump having an inlet, an outlet, a first pumping circuit and a second pumping circuit, the pumping circuits each being in fluid communication with the inlet and the outlet, and each being adapted to deliver the fuel to the engine; h

a positive displacement pump positioned in the first pumping circuit to pump the fuel therethrough;

a centrifugal pump positioned in the second pumping circuit to pump the fuel therethrough;

a shutoff valve fluidly connected to the inlet and the second circuit for preventing a flow of fuel from the inlet to the second circuit, the shutoff valve being remotely located from the first circuit so as not to impede an input flow thereto; and

13. The combination, as defined in claim 112, wherein the unitized pump further includes:

lid

higher of the respective pressures downstream of the metering devices during operation of the positive displacement pump.

M. The combination, as defined in claim 112, wherein the unitized pump further includes:

a third pumping circuit adapted to fluidly communicate with the inlet and the outlet;

a low-flow centrifugal pump positioned in the third pumping circuit to pump fuel therethrough from the inlet to the outlet; and

a positionable selector operatively connected to the second and third pumping circuits for directing an input flow from the inlet to either the second or third pumping circuits.

l5. The combination, as defined in claim M, further includ ing:

means responsive to the total flow in the fuel lines to control the position of the selector.

116. The combination, as defined in claim M, further including:

means to maintain a constant pressure differential between the pressure at the outlet of the unitized pump and the higher of the respective pressures downstream of the metering devices during operation of the low-flow pump.

17. A unitized pump for pumping a fluid comprising:

an inlet conduit;

an outlet conduit;

a first pumping circuit adapted to communicate with the inlet and outlet conduits;

a positive displacement pump having an inlet and an outlet positioned in the first pumping circuit to pump the fluid therethrough;

a second pumping circuit adapted to communicate with the inlet and outlet conduits;

a bypass circuit in fluid communication with the outlet and inlet of the positive displacement pump to bypass an outlet flow back to inlet;

a regulator valve mounted in the bypass circuit to control the flow therein; and

an unloading valve positioned in the bypass circuit inter mediate the regulator valve and the inlet of the positive displacement pump, the unloading valve being positionable to prevent a flow to the inlet of the positive displacement pump.

llfl. A pump, as defined in claim l7, wherein the positive displacement pump comprises:

a housing having a pumping cavity therein, the cavity communicating with the inlet and outlet of the positive displacement pump;

a pair of intermeshing gears disposed in the cavity; and

sealing means to move into peripheral engagement with the peripheries of the gears; and wherein there is further provided;

conduit means to interconnect the unloading valve and the sealing means to move the sealing means out of peripheral engagement with the gears.

19. A pump, as defined in claim 18, further including:

a third pumping circuit adapted to communicate with the inlet and outlet conduits; and

a low-flow centrifugal pump positioned in the third pumping circuit to pump the fluid therethrough.

20. A pump, as defined in claim 19, further including:

a shutoff valve disposed in fluid communication with the inlet conduit and operatively connected to the second and third pumping circuits for preventing an input flow thereto until at least one of the centrifugal pumps attains a predetermined speed, the shutoff valve being remotely located from the first pumping circuit so as not to impede an input flow thereto.

21. A pump, as defined in claim 19, further including:

drive means to drivingly interconnect the positive displacement pump with the centrifugal and low-flow centrifugal pumps.

22. A pump, as defined inclairn 19, further including:

a positionable selector operatively connected to both the second and third pumping circuits for directing an input flow to either the second or third pumping circuits.

23. A unitized pump for pumping a fluid comprising:

an inlet conduit;

an outlet conduit;

a high-flow centrifugal pump positioned in the second pumping circuit to pump the fluid therethrough;

a third pumping circuit adapted to communicate with the inlet and outlet conduits;

a low-flow centrifugal pump positioned in the third pumping circuit to pump the fluid therethrough; and

a shutoff valve disposed in fluid communication with the inlet conduit and operatively connected to the second and third pumping circuits for preventing a flow thereto until at least one of the centrifugal pumps attains a predetermined speed, the shutoff valve being located remote from the first pumping circuit so as not to impede a flow thereto from the inlet conduit.

24. A unitized pump for pumping a fluid comprising:

an inlet conduit;

an outlet conduit;

a firstpumping circuit adapted to communicate with the inlet and outlet conduits;

a low-pass centrifugal pump positioned in the third pumping circuit at a location downstream of the inlet conduit to pump the fluid therethrough;

a bypass circuit in fluid communication with the outlet and inlet of the positive displacement pump to bypass an outlet flow therefrom back to the inlet thereof; and

a regulator valve mounted in the bypass circuit to control the flow therein.

25. A pump, as defined in claim 24, further including:

drive means to drivingly interconnect the positive displacement pump with the high-flow and low-flow centrifugal pumps.

26. A pump, as defined in claim 24, further including:

a positionable selector operatively connected to the second and third pumping circuits for directing an input flow to either the second or third pumping circuits.

my UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,614,269 Dated October 19, 1972 M H Robert S. Lanctot It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 49, change Patent No. "2,705,259" to 2,105,259

Column 3, line 53, change "93" to 92 Column 5, line 51, change Patent No. "3,142,255" to 3,142,259

Column 8, line 39, delete include Column 12, line 10 (Claim 1, line 1), after "fluid" (first occurrence) insert to Column 12, line 14 (Claim 1, line 5) change "the other" to one Column 12, line 15 (Claim 1, line 6) change "high-flow" to low-flow Column 12, line 16 (Claim 1, line 7) change "one" to the other Column 12, line 42 (Claim 4, line 1) after "fluid" insert to a fluid Column 16, line 14 (Claim 24, line 15) change "low-pass" to low-flow Signed and sealed this 8th day of May 1973.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents

Claims

1. In a device for controlling the flow of a fluid a fluidconsuming load, the combination comprising: a unitized pump having two pumping circuits for delivering fluid to the load; a low-flow centrifugal pump positioned in the other of the circuits to pump the fluid therethrough; high-flow centrifugal pump positioned in one of the circuits to pump the fluid therethrough; a positionable selector operatively connected to both of the circuits for directing an input flow of the fluid to either the one or the other circuit; a pump selector signal generator operatively connected to the selector to generate a signal thereto for the positioning thereof; and means responsive to the total fluid flow delivered to the load to control the signal generator.

2. The combination, as defined in claim 1 wherein the unitized pump further comprises: an additional pumping circuit; a positive displacement pump positioned in the additional pumping circuit to pump the fluid therethrough; and a shutoff off valve disposed in fluid communication with the inlet of the pump and operatively connected to the first mentioned two pumping circuits for preventing an input flow thereto until at least one of the centrifugal pumps attains a predetermined speed, the shutoff valve being remotely located from the additional pumping circuit so as not to impede an input flow thereto.

3. The combination, as defined in claim 2, further including: means responsive to the speed of at least one of the centrifugal pumps to generate a speed signal to the shutoff valve for opening the shutoff valve.

4. In a device for controlling the flow of a fluid-consuming load, the combination comprising: a unitized pump having an inlet conduit, an outlet conduit, a first pumping circuit and a second pumping circuit, the pumping circuits each being in fluid communication with the inlet and outlet conduits and being adapted to deliver the fluid to the load; a positive displacement pump positioned in the first pumping circuit to pump the fluid therethrough; a centrifugal pump positioned in the second pumping circuit to pump the fluid therethrough; a metering system fluidly connected to the outlet conduit of the utilized pump for metering a flow of fluid to the load; a shutoff valve fluidly connected to the inlet conduit and the second circuit for preventing a flow of the fluid from the inlet conduit to the second circuit; and means to sense the speed of the centrifugal pump and generate a signal to open the shutoff valve when the centrifugal pump attains a predetermined speed.

5. The combination, as defined in claim 4, wherein the unitized pump includes: means to maintain a constant pressure differential across the metering system during operation of the positive displacement pump.

6. The combination, as defined in claim 4, wherein the unitized pump includes: a third pumping circuit; a low-flow centrifugal pump positioned in the third pumping circuit to pump the fluid therethrough from the inlet conduit to the outlet conduit; and a positionable selector operatively connected to both the second and third pumping cIrcuits for directing an input flow in the inlet conduit to either the second or third pumping circuit.

7. The combination, as defined in claim 6, further including: means responsive to the flow in the metering system to control the position of the selector.

8. The combination, as defined in claim 6, wherein the unitized pump includes: means to maintain a constant pressure differential across the metering system when the low-flow pump is in operation.

9. In an afterburning-type pump-control system for delivering fuel to an engine, the combination comprising: a unitized pump having an inlet, an outlet and two pumping circuits adapted to respectively communicate with both the inlet and the outlet; a high-flow centrifugal pump positioned in one of the circuits to pump the fuel therethrough; a low-flow centrifugal pump positioned in the other of the circuits to pump the fuel therethrough; a positionable selector operatively connected to both of the circuits for directing an input fuel flow from the inlet to either the one or the other circuits; two fuel lines fluidly connected to the outlet for receiving a flow of fuel therefrom; two metering devices respectively connected to the lines for metering fuel flows therethrough; a pump selector signal generator operatively connected to the selector to generate a signal thereto for the positioning thereof; and means responsive to the total fuel flow in the lines to control the signal generator.

10. The combination, as defined in claim 9, wherein the unitized pump further comprises: an additional pumping circuit adapted to communicate with the inlet and the outlet; a positive displacement pump positioned in the additional pumping circuit to pump the fuel therethrough; and a shutoff valve disposed in fluid communication with the inlet of the unitized pump and operatively connected to the first mentioned two pumping circuits for preventing an input fuel flow thereto until the engine attains a predetermined speed, the shutoff valve being remotely located from the additional pumping circuit so as not to impede an input flow thereto.

11. The combination, as defined in claim 10, further including: means responsive to the speed of the engine to generate a speed signal to the shutoff valve for opening the shutoff valve.

12. In an afterburning-type pump-control system for delivering fuel to an engine, the combination comprising: a unitized pump having an inlet, an outlet, a first pumping circuit and a second pumping circuit, the pumping circuits each being in fluid communication with the inlet and the outlet, and each being adapted to deliver the fuel to the engine; a positive displacement pump positioned in the first pumping circuit to pump the fuel therethrough; a centrifugal pump positioned in the second pumping circuit to pump the fuel therethrough; two fuel lines fluidly connected to the outlet for receiving a flow of fuel therefrom; two metering devices respectively connected to the lines for metering fuel flows therethrough; a shutoff valve fluidly connected to the inlet and the second circuit for preventing a flow of fuel from the inlet to the second circuit, the shutoff valve being remotely located from the first circuit so as not to impede an input flow thereto; and means to sense the speed of the centrifugal pump and generate a signal to open the shutoff valve when the centrifugal pump attains a predetermined speed.

13. The combination, as defined in claim 12, wherein the unitized pump further includes: means to maintain a constant pressure differential between the pressure at the outlet of the unitized pump and the higher of the respective pressures downstream of the metering devices during operation of the positive displacement pump.

14. The combination, as defined in claim 12, wherein the unitized pump further includes: a third pumping circuit adapted to fluidly communicate with the inlet and the outleT; a low-flow centrifugal pump positioned in the third pumping circuit to pump fuel therethrough from the inlet to the outlet; and a positionable selector operatively connected to the second and third pumping circuits for directing an input flow from the inlet to either the second or third pumping circuits.

15. The combination, as defined in claim 14, further including: means responsive to the total flow in the fuel lines to control the position of the selector.

16. The combination, as defined in claim 14, further including: means to maintain a constant pressure differential between the pressure at the outlet of the unitized pump and the higher of the respective pressures downstream of the metering devices during operation of the low-flow pump.

17. A unitized pump for pumping a fluid comprising: an inlet conduit; an outlet conduit; a first pumping circuit adapted to communicate with the inlet and outlet conduits; a positive displacement pump having an inlet and an outlet positioned in the first pumping circuit to pump the fluid therethrough; a second pumping circuit adapted to communicate with the inlet and outlet conduits; a centrifugal pump positioned in the second pumping circuit to pump the fluid therethrough; a bypass circuit in fluid communication with the outlet and inlet of the positive displacement pump to bypass an outlet flow back to inlet; a regulator valve mounted in the bypass circuit to control the flow therein; and an unloading valve positioned in the bypass circuit intermediate the regulator valve and the inlet of the positive displacement pump, the unloading valve being positionable to prevent a flow to the inlet of the positive displacement pump.

18. A pump, as defined in claim 17, wherein the positive displacement pump comprises: a housing having a pumping cavity therein, the cavity communicating with the inlet and outlet of the positive displacement pump; a pair of intermeshing gears disposed in the cavity; and sealing means to move into peripheral engagement with the peripheries of the gears; and wherein there is further provided; conduit means to interconnect the unloading valve and the sealing means to move the sealing means out of peripheral engagement with the gears.

19. A pump, as defined in claim 18, further including: a third pumping circuit adapted to communicate with the inlet and outlet conduits; and a low-flow centrifugal pump positioned in the third pumping circuit to pump the fluid therethrough.

20. A pump, as defined in claim 19, further including: a shutoff valve disposed in fluid communication with the inlet conduit and operatively connected to the second and third pumping circuits for preventing an input flow thereto until at least one of the centrifugal pumps attains a predetermined speed, the shutoff valve being remotely located from the first pumping circuit so as not to impede an input flow thereto.

21. A pump, as defined in claim 19, further including: drive means to drivingly interconnect the positive displacement pump with the centrifugal and low-flow centrifugal pumps.

22. A pump, as defined in claim 19, further including: a positionable selector operatively connected to both the second and third pumping circuits for directing an input flow to either the second or third pumping circuits.

23. A unitized pump for pumping a fluid comprising: an inlet conduit; an outlet conduit; a first pumping circuit adapted to communicate with the inlet and outlet conduits; a positive displacement pump positioned in the first pumping circuit to pump the fluid therethrough; a second pumping circuit adapted to communicate with the inlet and outlet conduits; a high-flow centrifugal pump positioned in the second pumping circuit to pump the fluid therethrough; a third pumping circuit adapted to communicate with the inlet and outlet conduits; a low-flow centrifugal pump positionEd in the third pumping circuit to pump the fluid therethrough; and a shutoff valve disposed in fluid communication with the inlet conduit and operatively connected to the second and third pumping circuits for preventing a flow thereto until at least one of the centrifugal pumps attains a predetermined speed, the shutoff valve being located remote from the first pumping circuit so as not to impede a flow thereto from the inlet conduit.

24. A unitized pump for pumping a fluid comprising: an inlet conduit; an outlet conduit; a first pumping circuit adapted to communicate with the inlet and outlet conduits; a positive displacement pump having an inlet and an outlet positioned in the first pumping circuit to pump the fluid therethrough; a second pumping circuit adapted to communicate with the inlet and outlet conduits; a high-flow centrifugal pump positioned in the second pumping circuit to pump the fluid therethrough; a third pumping circuit adapted to communicate with the inlet and outlet conduits; a low-pass centrifugal pump positioned in the third pumping circuit at a location downstream of the inlet conduit to pump the fluid therethrough; a bypass circuit in fluid communication with the outlet and inlet of the positive displacement pump to bypass an outlet flow therefrom back to the inlet thereof; and a regulator valve mounted in the bypass circuit to control the flow therein.

25. A pump, as defined in claim 24, further including: drive means to drivingly interconnect the positive displacement pump with the high-flow and low-flow centrifugal pumps.

26. A pump, as defined in claim 24, further including: a positionable selector operatively connected to the second and third pumping circuits for directing an input flow to either the second or third pumping circuits.