US3576375A

US3576375A - Fluid pumping system

Info

Publication number: US3576375A
Application number: US840752A
Authority: US
Inventors: Clive G B Jackson
Original assignee: Bendix Corp
Current assignee: Bendix Corp
Priority date: 1969-07-10
Filing date: 1969-07-10
Publication date: 1971-04-27
Anticipated expiration: 1988-04-27
Also published as: FR2054134A5; JPS506361B1; GB1317164A; DE2034427A1

Abstract

A pumping system for supplying fuel to the burners of aircraft jet engines. The system comprises a radially-vaned centrifugal pump and a peripheral vortex pump arranged in parallel to cooperatively deliver fuel under the correct pressure for all ranges of operation. The system includes sequential valving or clutching means so that at very low speeds (at ignition), the peripheral vortex pump supplies the fuel and at higher speeds, the radially vaned pump supplies the fuel.

Description

United States Patent [72] Inventor Clive G. B. Jackson 3,147,712 9/1964 Gaubatz 103/97 Clayville, NY. 2,785,634 3/1957 Marshall et a1. 415/143 [21] Appl. No. 840,752 2,464,144 3/1949 McConaghy 415/18 [22] July 1969 Primary Examinerl-Ienry F. Raduazo [45] Patented Apr. 27, 1971 Attorneys-Robert A. Benzlger and Plante, Arens, l-lartz, Hlx [73] Asslgnee The Bendix Corporation and Smith [54] FLUID PUMPING SYSTEM 4 Claims, 4 Drawing Figs.

[52] US. Cl. 415/18,

415/143 ABSTRACT: A pumping system for supplying fuel to the bur- Illtners of airc -laft jet engines The syslem comprises a radially. Fold 13/00 vaned centnfugal pump and a perlpheral vortex pump ar- Fleld ofSearch ranged in parallel to cooperatively deliver fuel unde the 287; 415/53, 18, 143-147; 103/11 (A), 97 rect pressure for all ranges of operation. The system includes sequential valving or clutching means so that at very low [56] Reta-films cued speeds (at ignition), the peripheral vortex pump supplies the 3 433 016 31:3 :3 SKATES PATENTS 60/241 ffiljel and at higher speeds, the radially vaned pump supplies the p q ore e 46 l 4 60 58 l 44 54. Q 66 6 o o o 77-7 so} //I4.

o o o 0 U 56 62 10 PATENTEUAPRZTIBYI 3576-375 SHEET 1 OF 3 ENGINE ACCELERATION LINE FIGURE 2 WHERE H= PUMP HEAD, FT

u IMPELLER PERIPHERAL SPEED, FT/SEC PERIPHERAL VORTEX HEAD COEFFIC! ENT 7 0 l l l l l NON-DI MENSIONAL FLOW Q/Qmux FIGURE l CLIVE JACKSON INVENTOR.

SHEET E OF L3 FIGURE 3 CLIVE JACKSON INVENTOR.

PATENTED APRZT 1971 SHEET 3 BF 3 FIGURE CLIVE JACKSON 1N VENTOR.

FLUID PUMPING SYSTEM SUMMARY OF THE INVENTION At present, the use of highspeed centrifugal fluid pumps to pump fuel to turbine engines has been limited to fuel supply pumping to the afterburner. This limitation is present because a centrifugal pump designed to generate the correct fuel I pumping pressure at engine operating speeds will not generate sufficient fuel pumping pressure at the engine lightoff speed (which may be as low as 10 percent of the operating speed). Centrifugal pumps are, however, extremely attractive in aircraft turbine fuel pumping applications because they are light in weight, sturdy, may be driven at very high speeds, and most importantly, they are insensitive to most contaminants carried by the fuel. It is, therefore, an object of this invention to provide a centrifugal pump or combination of centrifugal pumps as the main fluid pump in a system capable of supplying fuel to the burners of a turbine engine.

It is known that a positive displacement pump can be combined with a radially-vaned centrifugal pump to extend the lower range of operation of the pump system, but the positive displacement pumps are extremely sensitive to the presence of contaminants in the fluid being pumped. Furthermore, they require a gear and clutch connection to the drive of the pump so that they may operate at their optimum speed while the turbine is operating at low speed and may then be shut down after the radially-vaned centrifugal pump has reached its operated speed. It is, therefore, an object of this invention to provide a pumping system for pumping fluids which does not rely upon a positive displacement type of pump to supply pressurized fluid over the lower region of the operating speed range. It is a further object of this invention to provide a pumping system for a turbine engine which may be driven directly off of the same accessory drive shaft.

It is known that peripheral vortex pumps, also known as side channel pumps, regenerative pumps and regenerative turbine pumps, demonstrate a pumping characteristic in which, for a given speed, the head coefficient is inversely proportional to the normalized flow. Head coefficient is a direct function of the pumping pressure or head, while normalized flow is the actual flow divided by the maximum flow. On the other hand, a centrifugal pump, for a given speed, demonstrates a pumping characteristic of essentially constant head coefficient for all flows. This means that if a centrifugal pump were to be used for all conditions and were designed to produce adequate flow at the pressure necessary for engine lightoff, the pump would be very large and since for all rotodynamic pumps head is substantially proportional to the square of the speed and flow is substantially proportional to the speed, with gas turbine engines having a speed range of l:l, at normal operation, the pump would produce times the necessary flow and 100 times the necessary pressure. A peripheral vortex pump would, of course, suffer from the same operational conditions since it is but another type of rotodynamic'pump. Therefore, it

is clear that neither pump is adequate by itself. A more detailed discussion of the peripheral vortex and radially-vaned centrifugal pumps, taken with reference to FIGS. 1 and 2, may be found hereinbelow.

Because of the desirable characteristics of centrifugal pumps in general, it is an object of this invention to provide a fluid pumping system which incorporates a plurality of pump impellers of different designs which may be coaxially mounted and which will be capable of supplying fuel under the proper pressure to the burner nozzles of turbine engines at all engine operating conditions. More specifically, it is an object of this invention to provide, in a fluid supply system, a centrifugal pump and a peripheral vortex pump cooperatively coupled to pump fuel at the necessary pressure to the burner of a turbine engine. It is a still further object of the present invention to provide a fluid pumping system for supplying fuel to the burner of a turbine engine in which a peripheral vortex pump supplies fluid under pressure at low operating speeds and which is then disconnected from the pumping circuit in favor of a radially-vaned centrifugal pump once the operating speed has risen to the point that the radially-vaned centrifugal pump is capable at the necessary pressure.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows comparative curves of pump head coefiicient plotted as a function of normalized flow.

FIG. 2 shows comparative curves as shown in FIG. 1 for three values of pump speed.

FIG. 3 shows a preferred embodiment of my invention in schematic form wherein the peripheral vortex or starting pump is disconnected from the pump circuit by suitable valving and is subsequently permitted to run dry.

FIG. 4 shows, in schematic form, an alternative embodiment of my invention in which the starting pump impeller is coupled to and decoupled from the from the power input shaft by suitable clutch means.

DETAILED DESCRIPTION OF THE DRAWING With reference to FIGS. 1 and 2, the peripheral vortex pump, because of its internal regenerative action, has a much higher maximum head coefficient than the high-speed centrifugal pump. A comparison between the two is shown in FIG. 1. The centrifugal pump head curve appears flat because it would normally be plotted on a more expanded vertical scale. In both types of pump, flow is proportional to speed and head is proportional to the square of the speed.

Gas turbine engines usually have a speed range of about 10:1 between the beginning of the starting cycle and the rated speed, with idle speed at about 50 percent of rated speed. The fuel pressure required for the combustion system has a range of about 5:1 and the fuel pressure at idle is usually not much greater than that at the start.

A centrifugal pump designed to give the desired pressure at the start would, therefore, not only be very large because of its low head coefficient, but would generate about times the starting pressure at rated speed, or 10 times the required rated pressure.

Referring to FIG. 2, the lines N N and N are the head curves of a centrifugal pump at cranking, lightoff and idle speeds respectively. The lines N' N and N are the corresponding head curves of the peripheral vortex pump. The dashed line denoted as N represents the curve of required pressure versus flow for increasing engine speed.

The peripheral vortex pump is designed so that, at point P it is able to supply fuel at the necessary pressure. The centrifugal element, which is generating a very low pressure at this speed, is shut ofi by means of a discharge check valve or the like.

At point P, on the engine acceleration line, the peripheral pump has a head and flow capacity exceeding the requirement. A bypass valve would, therefore, be required to direct excess fuel flow to the peripheral pump inlet, permitting the pump to operate at point P on its head curve N At this speed, the centrifugal element is still incapable of supplying sufficient pressure and remain shut off.

At point P the greater part of the peripheral pump output is being bypassed but, at'this speed, the centrifugal pump is capable of supplying the required pressure, so the peripheral pump can now be shut down and vented.

Referring now to FIG. 3, my pump is shown in schematic fonn and is designated generally by 10. The pumping action is provided by starting section 12 containing impeller 14 and main section 16 containing impeller 18. The impellers l4 and 18 are attached to a shaft 20 for rotation therewith. In this instance, the

impellers

14 and 18 are of unitary construction,

nicate the starting section 12 with the passage 26. Fluid flow through

passages

28 and 30 is controlled by valve 44. The fluid discharge passage 34 communicates with the main section 16 through passage 36 and with the starting section 12 through passage 38. The passages or

conduits

36 and 38 are controlled by check valve means 40 and 42 so that during the range of the operating cycle when only one pumping section is supplying the fluid under pressure, the other pumping section does not provide a low pressure fluid dump. Branching off of delivery passage 38 is return passage means 31 controlled by bypass check valve 33 which permits excess fluid flow to be recirculated through the starting pump section 12.

Shutoff valve 44 is a portion of the control valve, indicated generally by 46, and is positioned in response to the fluid pressure in the output channel or collector ring 48 of the main pumping section 16. A pilot valve 50 is resiliently biased to close the outlet port of control passage 52 which intercommunicates control valve 46 and channel 48. Upon movement of the pilot valve 50, the fluid pressure in channel 48 is communicated to the piston end, indicated generally as 54, of control valve 46 and is operative to more control valve 46 and to thereby seal the inlet of passage 30 with shutoff valve 44.

The control valve 46 has, at the piston end 54, projecting abutment fingers 56 which allow the control valve 46 to be held away from the outlet of passage 52 so that fluid pressure in channel 48 can be communicated to the entire surface area of the piston portion. The control valve 46 is biased toward the outlet of channel 52 by spring 58 and the pilot valve 50 is biased by spring 60 to close the aforementioned outlet of passage 52. A passage 62 is arranged in the body of control valve 46 in order to communicate atmospheric pressure from channel 64 to the inlet of passage 30 when valve 44 has sealed passage 30 from communication with the pump inlet passage 26. An annular recess 66 is also provided in the body of control valve 46 so that the passage 63 can communicate the delivery passage 38 of the starter pumping section 12 with the drain passage 70 whenever the shutoff valve 44 is seated so that when atmospheric pressure is being communicated to passage 30 by passage 64 through passage 62, the starter impeller can be drained of fluid.

Referring now to FIG. 4, an alternative embodiment of my invention is shown in which the use and operation of the starting impeller 114 is controlled by clutch means 146. In this embodiment, passage 128 communicates the pump inlet passage 126 to the starting impeller 114, while passage 131 communicates additional flow from the outlet of the starting impeller 114 to the inlet of the starting impeller 114. In this embodiment, control clutch means 146 are operative to couple starting impeller 114 to the shaft 120 for rotation therewith and to decouple starting impeller 114 from the shaft 120 when its pumping action is no longer necessary.

As can be readily seen, my fluid pumping system is composed of four separately functioning elements, the fluid passage means to supply fluid to and receive fluid from the pump, a starting impeller and a main impeller and the impeller controlling means. In the FIG. 3 embodiment, the impeller controlling means comprised various flow control valves and exhaust passages, while in the FIG. 4 embodiment, the impeller controlling means comprised a clutch means to couple the impeller to and to decouple it from the power input shaft. The clutch 146 utilized in the FIG. 4 embodiment may be a centrifugal clutch in which the interconnection of clutch input and output components is terminated above rotational speeds of a selected value and the interconnection is completed, as for instance, by a resilient or other biasing means below the selected speed. The clutch 146 could also be electromagnetically actuated so that a friction connection exists whenever an electromagnetic coil is energized and energization of the coil could be controlled manually or automatically in response to the speed of shaft 120. Examples of both types of clutches, as well as further alternatives, are well known and further description is not considered necessary.

OPERATION OF THE FIG. I EMBODIMENT Assuming initial fluid flow through passage 26, the operation of my pumping system is as follows: Rotation of the shaft 20 causes rotation of the impellers l4 and 18. Rotation of impeller 18 produces a low pressure gradient across the impeller 18 and is, therefore, of little consequence. Impeller 14, on the other hand, produces a suction which draws fluid from passage 26 through

passages

28, 30 and 32, and causes an increase in fluid pressure in passage 38. The starting pump shutoff valve 44 is withdrawn from the inlet port of passage 30 and the starting pump bypass valve means 33 and check valve means 42 are biased closed. When the pressure reaches a predetermined minimum, check valve means 42 opens and fluid begins to pass through the discharge conduit 34. In the event that the pressure in passage 38 becomes excessive, bypass valve means 33 opens to establish a recirculating flow.

While impeller 14 has started to pump fluid through the discharge passage 34, the check valve 40 has remained closed and pressure in channel 48 has begun to increase. At a predetermined point, the pressure in channel 48 and passage 52 will exceed the spring pressure of spring 60 and the pilot valve 50 will be forced away from the outlet of passage 52. The fluid will then force the control valve 46 to the right, as shown in the drawing, when the fluid pressure exceeds the force of spring 58. As the control valve moves rightward, passage 68 will be connected to the drain passage 70 by annular recess 66 in the body of the control valve and inlet to passage 30 will be closed to fluid and opened to the atmosphere through passages 62 and 64. Check valve means 33 and 42 will close when the pressure in passage 38 drops below the check valve threshold values. As the impeller 14 continues to rotate, it will pump itself dry through passage 68, thus eliminating fluid resistance in the starter pumping section 12.

The spring constants of the springs controlling the pilot valve 50, control valve 46, and check valve 40 will be such that they will resist movement of the various valves until impeller 18 is generating sufficient pressure and capacity to supply all the fuel requirements of its associated turbine.

The pump, according to the present invention, combines the advantages of almost complete insensitivity to contaminants with a lower weight and smaller possible envelope because it does not need the gear connection between main pump and starting pump. The control valve means and fluid exhaust passage means need not be large or close to the impellers so that they do not impose a significant weight or envelope problem. The arrangement of valves and passages herein described is not to be considered as the only method of achieving the desired functions, but is an example of my invention, the scope of which is defined by the claims which follow.

It will be observed that the FIG. 4 embodiment of my invention achieves the sequential pumping by use of a control clutch 146 in place of the control valve 46. In applications where fuel contamination is a serious problem, the elimination of control valve 46 permits my pump to become even less sensitive to fuel contaminants while the clutched connection between the starting impeller 114 and the main shaft permits the starting impeller to be nonrotating during most of the period of time the engine is operating.

As will be readily observed from FIGS. 3 and 4 and from the preceding description, the impellers provide substantially sequential pumping and are arranged in parallel fashion so as to remain substantially independent from one another. However, to provide a continuous range of pumping, there will be a region of overlap in which each impeller is providing a portion of the pressurized fluid. Because a peripheral vortex type of rotodynamic impeller provides a very high head coefficient at low flows, which would readily correspond to fuel flow in a gas turbine at engine lightoff, a peripheral vortex impeller is the preferred form of impeller 14 for the starting section 12 of my fluid pump, taking into consideration envelope restrictions imtype of rotodynamic impeller, on the other hand, maintains a substantially-constant head coefficient over its entire flow range and is, therefore, my preferred form of main section impeller 18.

In order to provide the necessary flow range at sufficient fluid pressure to provide fuel having pressures sufficient for all operating ranges of a gas turbine engine, from lightoff to maximum speed, I have combined a plurality of rotodynarnic impellers having dissimilar head coefficient versus normalized flow curves.

l claim:

1. Fluid pumping apparatus having fluid inlet and fluid discharge passages comprising:

pump housing means including first and second chambers having fluid inlet means and fluid exhaust means;

said first and second chambers and said fluid inlet means and discharge means arranged in parallel and interconnecting the fluid inlet and fluid discharge passages;

first and second dissimilar rotodynamic impellers rotatably contained within said first and second chambers;

means for driving said impellers; and

control means responsive to fluid pressure in one of said chambers operative to control the flow of fluid from the fluid inlet passage, through the fluid inlet means and fluid exhaust means and out through the fluid discharge passage.

2. The apparatus as claimed in claim 1 wherein said control means comprise:

flow controlling valve means operative to terminate fluid delivery to said first chamber means when the fluid pressure in said second chamber means reaches a predetermined level.

3. The apparatus as claimed in claim 2 including further venting means associated with said first chamber means operative to communicate the fluid inlet of said first chamber means to the atmosphere and the fluid outlet of the first chamber means to a fluid drain.

4. The apparatus as claimed in claim 11 wherein said second rotodynamic impeller produces a pumping characteristic wherein the head coefficient is substantially constant for all flows.

Claims

1. Fluid pumping apparatus having fluid inlet and fluid discharge passages comprising: pump housing means including first and second chambers having fluid inlet means and fluid exhaust means; said first and second chambers and said fluid inlet means and discharge means arranged in parallel and interconnecting the fluid inlet and fluid discharge passages; first and second dissimilar rotodynamic impellers rotatably contained within said first and second chambers; means for driving said impellers; and control means responsive to fluid pressure in one of said chambers operative to control the flow of fluid from the fluid inlet passage, through the fluid inlet means and fluid exhaust means and out through the fluid discharge passage.

2. The apparatus as claimed in claim 1 wherein said control means comprise: flow controlling valve means operative to terminate fluid delivery to said first chamber means when the fluid pressure in said second chamber means reaches a predetermined level.

4. The apparatus as claimed in claim 1 wherein said second rotodynamic impeller produces a pumping Characteristic wherein the head coefficient is substantially constant for all flows.