US3679329A

US3679329A - Flat side valve for a pump

Info

Publication number: US3679329A
Application number: US44268A
Authority: US
Inventors: Gilbert H Drutchas; George A Berman; Phillip B Spencer
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1970-06-08
Filing date: 1970-06-08
Publication date: 1972-07-25
Anticipated expiration: 1989-07-25
Also published as: JPS5210202B1; DE2109246A1; CA924184A; BR7101926D0; FR2095994A5; ES389081A1; GB1302984A

Abstract

Two confronting relatively movable radial surfaces formed by a stationary pressure part and a movable valve part respectively, have an axially projecting circumferentially continuous shoulder formed on one of the parts and disposed between the surfaces to partition the space between the two parts into an inlet zone and an outlet zone. The valve part is moved axially as a function of fluid flow to by-pass fluid directly across the shoulder into the inlet zone from the outlet zone.

Description

United States Patent Drutchas et al.

[ 1 July 25,1972

54] FLAT SIDE VALVE FOR A PUMP 2,380,783 7/1945 Painter ..4|7 3|0 4 0 68 t [72] inventors: Gilbert H. Drutchas, Birnungham; George 23232 21: a] A. Benn, Detroit; Pump B. Spencer,

R alO k,all fM h. 0y 3 o v Primary Examiner-Carlton R. Croyle Asslgneei TRW Cleveland, Ohio Assistant Examiner-John J. Vrablik [22] Filed: June 8 1970 Attorney-Hill, Sherman, Meroni, Gross & Simpson [21] Appl. No.: 44,268 [57] ABSTRACT Two confronting relatively movable radial surfaces formed by I U-S. "417/300, 4 1 l 0 a tationary press u-e pan and a movable valve pan respective- 51 lnt. (,l ..F04b 49/00 1y, have an axially projecting circumferentiany continuous [58] dd 0' Search l 37/] 17, fl97; 4l7/53, 300, Shoulder formed on one of the parts and disposed between the 417/304 310 surfaces to partition the space between the two parts into an 6 R f Ct d inlet zone and an outlet zone. The valve part is moved axially [5 1 e erences e as a function of fluid flow to by-pass fluid directly across the UNITED STATES PATENTS shoulder into the inlet zone from the outlet zone.

3,125,028 3/1964 Rohde ..4l7/300 6 Claims, 8 Drawing Figures 12 III 17 IE 14 n .71

Z126 2 22 AW 30 17 l I jg l7 i? v a4 1? i 57 f J0 zZ .JF 1.1.! I m PATENTEDJMS m2 BEST AVAILABLE COPY 3.679.329

sum 1 or 3 FLAT SIDE VALVE FOR A PUMP BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to a combined pump and valving structure, for example, a power steering pump having an integral flow control valve embodied therein.

2. The Prior Art The prior art in regard to which the present invention constitutes an improvement is exemplified by various patents issued to the same assignee of the present invention such as Clark and Drutchas Pat. Nos. 3,200,752 and 3,273,503. In those patents, there is disclosed a power steering pump utilizing a stackup of parts and wherein a plate constituting the outermost part carries a flow control valve.

SUMMARY OF THE INVENTION The present invention is based upon a so-called flat side valve concept wherein two confronting relatively movable radial surfaces formed by a pressure part and an adjoining valve part are partitioned by a circumferentially continuous shoulder disposed therebetween in order to provide inner and outer zones. Thus, fluid at pump generated pressure is directed into one of the zones, for example, the innermost zone while the outer zone is vented back to the pump inlet. It is further contemplated by the present invention that a flow control orifice be formed in the valve part thereby to direct all of the fluid discharged by the pump through the flow control orifice so that the valve part may be movable as a function of the pressure drop across the orifice thereby to selectively separate the radial surfaces and directly by-pass fluid from the outlet zone across the shoulder to the inlet zone.

It is further contemplated by the present invention that a plunger construction be provided in the valve part controlling the magnitude of the flow set by a variably regulated orifice and thereby providing a constant pressure relief. By virtue of the arrangement provided, a highly responsive flow control valve with linear characteristics is supplied. Moreover, means are thus provided for reducing pump internal back pressure. The flow control system of the present invention affords zero leakage at minimum or maximum line pressures and the flat side valve concept provides a valving geometry that is conveniently and economically produced in accordance with accepted mass production fabricating techniques.

The overall pump and valve package also provides a valving structure that takes less physical space than current commercial side manifolded valves thus reducing measurably the axial assembly length of the pump and valve package and permitting the unit to be advantageously exploited in cramped quarters.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 4 is an alternative form of a pressure part illustrating how a partitioning shoulder may be disposed on the pressure part instead of on the valve part as illustrated in FIG. 1;

FIG. 5 is a cross sectional view taken on line V--V of FIG.

FIG. 6 is a view taken on line VI-VI of FIG. 1 and showing only additional details of the valve part, other parts being removed for the sake of clarity;

FIG. 7 is a fragmentary cross sectional view taken on line VIIVII, again with parts removed but showing additional details of the valve part of the present invention; and

FIG. 8 is a fragmentary cross sectional view taken on line Vlll-Vlll of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Although the principles of the present invention are of general application, a particularly useful application is made to a power steering pump wherein the output of the pump is regulated as a function of fluid flow. Accordingly, the exemplary structure illustrated herein by means of which the present invention may be described constitutes a power steering pump shown generally at 10 and including a housing 11 having a radial face 12 against which is engaged a flange 13 of a generally cup-shaped enclosure 14. The enclosure 14 is fastened to the housing 11 by a plurality of bolts 16.

The housing 11 has an axially extending boss 17 in which is disposed a sleeve bearing 18 for joumalling a shaft 19. The usual shaft seal is shown generally at 20 and it will be understood that the shaft 19 can be connected to any rotational drive, such as the fan belt of an internal combustion engine in a vehicle.

lnwardly of the enclosure 14 and adjacent the flat surface 12 of the housing 11 there is provided a stackup of parts constituting a pump-Thus, there is provided a first pressure plate member 21, a ring member 22 and a second pressure plate member indicated at 23. The three

parts

21, 22 and 23 are each appropriately apertured for the purpose of passing dowel pins shown at 24 and each of which is threaded into corresponding recesses 26 formed in the housing 11. Each dowel pin 24 has a flange 27 formed thereon which overlies the second pressure plate 23. Projecting axially from each respective flange 27 is a pilot portion 28 received in corresponding openings 29 of a valve part shown generally at 30.

Referring to FIG. 2 in conjunction with FIG. I, it will be noted that the ring 22 has a double-lobed pumping chamber formed therein as at 31. Rotatable within the pumping chamber 31 is a rotor 32 having a plurality of generally rectangular notches 33 formed therein each of which receives a pumping element 34 which is sized with respect to each notch 33 so as to move radially and rock angularly while following the adjoining bore wall of the pumping chamber 31. Each pumping element 34 is loaded by a spring 36. It will be noted that the rotor 32 is keyed as at 37 to one end of the shaft 19 which projects beyond the radial wall 1-2 into the center opening of the rotor.

Disposed between the valve part 30 and the enclosure 14 is a sealing member 38- (FIG. 1) thereby dividing the interior of the enclosure 14 into a high pressure area 39 and a low pressure area 40. A discharge member such as a nipple 41 is connected to a radial end wall 42 of the enclosure-14 and has a discharge passage 43 so that high pressure fluid from the high pressure zone 39 may be conducted to a point of utilization, such as a power assisted steering mechanism in a dirigible vehicle.

The low pressure zone 40 conveniently provides an inlet area for the pump and in this regard, it will be noted that the pressure plate 23 is notched as at 44,44 as shown in the first and third quadrants in the view of FIG. 3 thereby to communicate inlet fluid into corresponding inlet portions of the double-lobed pumping chamber 31. The

notches

44,44 also communicate with radially inwardly disposed inlet ports shown at 46,46, thereby to assist in filling the space behind the pumping elements 34 in the notches 33 of the rotor 32.

In the second and fourth quadrants, again using the orientation of FIG. 3, it will be noted that the pressure plate 23 has

outer discharge ports

47,47 and

inner discharge ports

48,48, each inner discharge port having a precompression notch 49 to permit a low rate pressure buildup in the pumping bore between the inlet 44 and the outlet 47.

By virtue of the double-lobed pumping configuration provided by the pump 10, it will be appreciated that there are two pumping impulses for each rotation of the rotor 32 and accordingly, fluid at pump generated pressure is discharged from the

outlet ports

47 and 48.

in accordance with \the principles of the present invention, a flat side valve concept is exploited. Thus, the pressure plate 23 constitutes a first stationary pressure part having a radial face 50. The valve part 30 constitutes a movable valve part having a radial face 51. Thus, the two confronting relatively movable radial faces or

surfaces

50 and 51 are formed respectively by the stationary presure part and the movable valve part.

It, is further contemplated by the present invention that therebe provided an axially projecting circumferentially continuous shoulder on one of thetwo parts which is disposed between the confronting surfaces thereby to partition the space between the confronting surfaces intoan inlet zone and an outlet zone. In FIG. 1, the axially projecting shoulder is provided at 52 andis formed on the valve part, thereby to projectaxially from the surface 51 toward the surface 50.

Referring to FIGS. 1, 3 and 6 in conjunction with one another, it will be noted that the shoulder 52 is circumferentially continuous but is not formed in the shape of a regular circle: Rather, the shoulder 52 is disposed in a more or less rectangular fashion so that it borders the respective inletand

outlet ports

46 and 47, thereby providing an inner outlet zone 53 and an outer inlet zone 54. Accordingly, all of the

outlet ports

47,47, 48,48 communicate with the outlet zone 53 while the

corresponding inlet ports

44,44, 46,46 communicate with the inlet zone 54. That part of the face 51 which is in the outlet zone 53 is shown at 53a and the corresponding part of the face 50 is shown at 53b. i

ln practicing the flat side valve concept of the present invention, it will be readily appreciated by those skilled in the art that the axially projecting shoulder may be reversed and may be situated on the stationary pressure part also. Accordingly, the alternative construction is shown in FIGS. 4 and wherein a stationarypressure part is shown at 230, all of the likeparts being designated by like numbers but with the suffix a. With such an arrangement, it will be appreciated that the valve part would be provided :with a flat, radial surface and the radial surface 50a of the pressure part 23a would be characterized'by the axially projecting shoulder 52a.

Referring now to FIGS. 6 and 7, additional details of the valve part 30 are shown. First of all, the valve part has a centrally disposed bore shown at 60 and which bore intersects the radial surface 51 thereby to provide a valve seating edge 61 which'forms the edge of an orifice shown at 62.

-Axially inwardly of the orifice 62, the bore 60 has an enlarged annulus 63. The bore 60 is successively counterbored as at 64 and 65 respectively Slidably mounted within the bore 60 is a plunger shown generally at 66. The plunger 66 has an outer peripheral surface 67' which includes a tapered valve seat 68 contracting down to a reduced diameter peripheral surface 69 which is very close in dimension to the internal diameter of the bore 60. Thus, the tapered valve surface 68 cooperates with the valve seating edge 61, thereby to selectively change the orifice 62 when the plunger 66 is moved relative to the bore 60 and making the orifice 62 a variably sized orifice.

- The peripheral surface of the plunger 66 is recessed to receive an O-ring sealing member 70 engageable with the walls of the bore 60. The plunger 66 terminates in a still further reduced diameter portion 71 thereby leaving a radial shoulder 72 against which is seated a backing ring 73 bottoming one end of a spring 74. The opposite end of the spring 74 is bottomed against a cap member 76 having axially extending side walls 77 received in the counterbore 65.

The plunger 66 has a passage extending therethrough which is identified at 78. Situated within the passage 78 is a square rod 79. One end of the rod 79 engages against the cap member 76 while the other end engages against a ball valve 80. The ball valve 80 is biased by a coil spring 81 against a tapered valve seat 82 formed in the passage 78 and the opposite end of the spring 81 is engaged by a retainer disk 83 held in the end of the plunger 66.

A coil spring .84 engages a rear wall of the valve part and is disposed radially outwardly of the cap 76. A plurality of passages in the form of circumferentially spaced apertures are provided at 86 and lead from the annulus 63-to the rear wall 87, which rear wall 87 forms one boundary of the pressure discharge area 39 isolated by the sealing member 38.

The recess shown at 88 inwardly of the cap 76 is vented to the inlet zone by one or more passages 89 extending through the valve part 30 from the recess 88 to a location outwardly of the shoulder 52.

In operation, flow emanating from the pump outlet ports'47 and 48 issues into the outlet zone 53. The flow is normally directed through the orifice 62 around the plunger 66'and into the annulus 63 whereupon the flow goes through the passages 86 into the pressure discharge area 39 and thence through the nipple fitting 41 and more particularly the passage 43 formed therein to the outlet line beyond. I

- As pump output flow rises through the orifice 62, the pressure drop across the orifice 62 increases. The rising dynamic pressure drop references an increasing force on the surface 51 while atmospheric pressure prevails on the surface of the rear wall 87. Accordingly, the valve part 30 moves. open against the spring 84 and achieves a predetermined flow output to the discharge area 39. The magnitude of the flow is set by the orifice size 62 and by the force on the spring 84. I

A restriction anywhere downstream of the orifice 62 will create a pressure on the face of the plunger 66 and on the surface corresponding to the end surface thereof. As the pressure rises, the plunger 66 is held in fixed position by the reaction force developed by the spring 74 and the cap member 76 up to the preload value of the spring 74. Any pressure above the setting of the spring 74 causes the plunger 66 to move in a direction of the applied pressure. Since the square rod 79 is stationary, the movement of the plunger 66 which is sealed by theO-ring 70 unseats the ball valve whilesimultaneously effecting a closure of the plunger valve heat seating surface 68 on the valve seating edges 61. Any pressure trapped between the plunger valve head seating surface 68-and the downstream extremity of a pressure line extending from nipple 41 is unloaded through an orifice 91 which interconnects the passage 86 to the low pressure recess 88 when the ball valve 80 is unseated by the square rod 79.

The area 39 rearward of the valve part 30, the passages 86, the annulus 63 and the recess 88 and the passage 89 are all connected to atmospheric pressure. Accordingly, the pressure differential between the surface 51 and the rear wall 87 results in an opening motion of the valve part 30. In this manner, a constant relief pressure is effected. 7

Referring to the drawings, by-pass from the pump output at high pressure from within the outlet zone flows over the axial projecting shoulder 52 and over the inlet opening I. The high velocity stream A passes over the shoulder 52 in such a manner as to provide an aspirating area B which induces a flow C through a passage P, thereby to achieve a su-' percharging effect. As shown on FIG. 6 taken in conjunction with FIG. 8, the passage P" may be provided on both sides of the valve plate.

Although minor modifications might be suggested by those versed in the art, it should be understood that we wish to 'embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of our contribution to the art.

We claim as our invention:

1. A rotatable pump having an axis of rotation comprising, two confronting relatively movableradial surfaces formed by a stationary pressure part and a movable valve part, respectively, an axially projecting circumferentially continuous shoulder formed on one of said parts and disposed between said surfaces to partition the space therebetween into an inner outlet zone and an outer inlet zone,

outlet port means in said pressure part for discharging fluid at pump generated pressure into said outlet zone, inlet port means communicating with said inlet zone,

means including said valve port forming an orifice through which all of the fluid discharged by the pump is directed, thereby to provide a pressure drop across said orifice,

said valve part having a rear surface forming one wall of a discharge space receiving fluid from said orifice and from which fluid is directed to a point of utilization, a separate relief valve carried in said valve part and operable to close said orifice in response to changes in pressure differential between opposite sides of said valve part, and

control spring means acting on said rear surface of said valve part together with said fluid whereby said valve part is selectively moved in response to changes in pressure drop across said orifice to separate said radical surfaces and by-pass fluid directly across said shoulder to said inlet zone.

2. A rotatable pump having an axis of rotation comprising,

a housing having a flat radial surface,

a stack-up of parts comprising a ring forming a pumping chamber and a pressure part having outlet port means formed therein,

a rotor in said ring having a notched periphery, pumping element means carried in the notched periphery and which pumping element means are free to move radially and to rock angularly while following the adjacent wall of the pump chamber,

inlet port means communicating with the exterior periphery of said pressure part,

enclosure means connected to said housing and forming an inlet zone aroundsaid ring and said pressure part,

a movable valve part adjacent said pressure part, a spring between said enclosure means and said valve part loading said valve part toward said pressure part,

said valve part and said pressure part having rigid confronting relatively movable radial surfaces,

an axially projecting circumferentially continuous shoulder formed on one of said surfaces and normally in contact with the other of said surfaces to partition the space therebetween into an inner outlet zone communicating with said outlet ports and an outer inlet zone communicating with said inlet ports, means including said valve part forming within the confines of said shoulder a variable orifice the size of which varies with the pressure drop across the orifice through which all of the fluid discharged by the pump is directed thereby to produce a pressure drop across said orifice, sealing means between said enclosure and said valve part for separating the interior of said enclosure into an inlet area and a discharge area,

said valve part having a rear surface forming one wall of the discharge area receiving fluid from the orifice and from which fluid is directed to a point of utilization,

whereby said valve part is selectively moved in response to changes in pressure drop across said orifice to separate said shoulder from the other of said surfaces and by-pass fluid directly across said shoulder from said outlet zone to said inlet zone.

3. A rotatable pump having an axis of rotation comprising,

two confronting relatively movable rigid radial surfaces formed by a stationary pressure part and a movable valve part, respectively,

an axially projecting circumferentially continuous shoulder formed on one of said surfaces, and normally in contact with said other surface to partition the space therebetween into an inner outlet zone and an outer inlet zone,

outlet port means in said pressure part for discharging fluid at pump generated pressure into said outlet zone,

inlet port means communicating with said inlet zone, means including said movable valve part forming within the confines of said shoulder, a variable orifice, the size of which varies with the pressure drop across the orifice, through which all of the fluid discharged by the pump is directed, thereby to provide a pressure drop across said orifice,

said movable valve part having a rear surface forming one wall of a discharge space receiving fluid from said orifice and from which fluid is directed to a point of utilization,

and control spring means acting on said rear surface together with said fluid whereby said movable valve part is selectively moved in response to changes in the pressure drop across said orifice to vary the size of said orifice and to separate said radial surfaces and by-pass fluid directly across said shoulder. 4. In a pump as defined in claim 3, said valve part having an inlet opening formed therein outwardly adjacent said shoulder so that high velocity flow by-passed across said shoulder and between said radial surfaces will flow over said inlet opening to provide an aspirating area for inducing the flow of fluid thereinto, and a passage extending from the rear of said valve part to said inlet opening through which fluid is aspirated.

5. A rotatable pump having an axis of rotation comprising, two confronting relatively movable radial surfaces formed by a stationary pressure part and a movable valve part, respectively,

an axially projecting circumferentially continuous shoulder formed on one of said parts and disposed between said surfaces to partition the space therebetween into an inner outlet zone and an outer inlet zone, outlet port means in said pressure part for discharging fluid at pump generated pressure into said outlet zone, inlet port means communicating with said inlet zone, said valve part having formed therein inwardly of said shoulder an axially extending bore intersecting said radial surface to form an annular valve seating edge, said bore having an enlarged annulus formed therein axially inwardly of said valve seating edge,

and said bore terminating in a counterbore, said valve part further including a rear face outwardly of said counterbore,

a cap member in said counterbore,

a coil spring bottomed at one end against said cap member,

a plunger slidable in said bore and engaging the other end of said spring, said plunger having a radially tapered valve head surface cooperable with said valve seating edge to form a variable orifice,

and passage means in said valve part from said annulus to said rear face,

enclosure means forming with said rear face a discharge cavity leading to a point of utilization,

and spring means between said enclosure means and said rear face whereby said valve part is movable in response to changes in the pressure drop across said orifice.

6. A pump as defined in claim 5 and further characterized by said plunger having a passage formed therein,

a ball valve in said passage,

a spring loading said ball valve closed and a rod in said passage having one end engaged against said cap and the other end against said ball valve, whereby constant relief pressure is effected.

Claims

1. A rotatable pump having an axis of rotation comprising, two confronting relatively movable radial surfaces formed by a stationary pressure part and a movable valve part, respectively, an axially projecting circumferentially continuous shoulder formed on one of said parts and disposed between said surfaces to partition the space therebetween into an inner outlet zone and an outer inlet zone, outlet port means in said pressure part for discharging fluid at pump generated pressure into said outlet zone, inlet port means communicating with said inlet zone, means including said valve port forming an orifice through which all of the fluid discharged by the pump is directed, thereby to provide a pressure drop across said orifice, said valve part having a rear surface forming one wall of a discharge space receiving fluid from said orifice and from which fluid is directed to a point of utilization, a separate relief valve carried in said valve part and operable to close said orifice in response to changes in pressure differential between opposite sides of said valve part, and control spring means acting on said rear surface of said valve part together with said fluid whereby said valve part is selectively moved in response to changes in pressure drop across said orifice to separate said radical surfaces and bypass fluid directly across said shoulder to said inlet zone.

2. A rotatable pump having an axis of rotation comprising, a housing having a flat radial surface, a stack-up of parts comprising a ring forming a pumping chamber and a pressure part having outlet port means formed therein, a rotor in said ring having a notched periphery, pumping element means carried in the notched periphery and which pumping element means are free to move radially and to rock angularly while following the adjacent wall of the pump chamber, inlet port means communicating with the exterior periphery of said pressure part, enclosure means connected to said housing and forming an inlet zone around said ring and said pressure part, a movable valve part adjacent said pressure part, a spring between said enclosure means and said valve part loading said valve part toward said pressure part, said valve part and said pressure part having rigid confronting relatively movable radial surfaces, an axially projecting circumferentially continuous shoulder formed on one of said surfaces and normally in contact with the other of said surfaces to partition the space therebetween into an inner outlet zone communicating with said outlet ports and an outer inlet zone communicating with said inlet ports, means including said valve part forming within the confines of said shoulder a variable orifice the size of which varies with the pressure drop across the orifice through which all of the fluid discharged by the pump is directed thereby to produce a pressure drop across said orifice, sealing means between said enclosure and said valve part for separating the interior of said enclosure into an inlet area and a discharge area, said valve part having a rear surface forming one wall of the discharge area receiving fluid from the orifice and from which fluid is directed to a point of utilization, whereby said valve part is selectively moved in responSe to changes in pressure drop across said orifice to separate said shoulder from the other of said surfaces and by-pass fluid directly across said shoulder from said outlet zone to said inlet zone.

3. A rotatable pump having an axis of rotation comprising, two confronting relatively movable rigid radial surfaces formed by a stationary pressure part and a movable valve part, respectively, an axially projecting circumferentially continuous shoulder formed on one of said surfaces, and normally in contact with said other surface to partition the space therebetween into an inner outlet zone and an outer inlet zone, outlet port means in said pressure part for discharging fluid at pump generated pressure into said outlet zone, inlet port means communicating with said inlet zone, means including said movable valve part forming within the confines of said shoulder, a variable orifice, the size of which varies with the pressure drop across the orifice, through which all of the fluid discharged by the pump is directed, thereby to provide a pressure drop across said orifice, said movable valve part having a rear surface forming one wall of a discharge space receiving fluid from said orifice and from which fluid is directed to a point of utilization, and control spring means acting on said rear surface together with said fluid whereby said movable valve part is selectively moved in response to changes in the pressure drop across said orifice to vary the size of said orifice and to separate said radial surfaces and by-pass fluid directly across said shoulder.

4. In a pump as defined in claim 3, said valve part having an inlet opening formed therein outwardly adjacent said shoulder so that high velocity flow by-passed across said shoulder and between said radial surfaces will flow over said inlet opening to provide an aspirating area for inducing the flow of fluid thereinto, and a passage extending from the rear of said valve part to said inlet opening through which fluid is aspirated.

5. A rotatable pump having an axis of rotation comprising, two confronting relatively movable radial surfaces formed by a stationary pressure part and a movable valve part, respectively, an axially projecting circumferentially continuous shoulder formed on one of said parts and disposed between said surfaces to partition the space therebetween into an inner outlet zone and an outer inlet zone, outlet port means in said pressure part for discharging fluid at pump generated pressure into said outlet zone, inlet port means communicating with said inlet zone, said valve part having formed therein inwardly of said shoulder an axially extending bore intersecting said radial surface to form an annular valve seating edge, said bore having an enlarged annulus formed therein axially inwardly of said valve seating edge, and said bore terminating in a counterbore, said valve part further including a rear face outwardly of said counterbore, a cap member in said counterbore, a coil spring bottomed at one end against said cap member, a plunger slidable in said bore and engaging the other end of said spring, said plunger having a radially tapered valve head surface cooperable with said valve seating edge to form a variable orifice, and passage means in said valve part from said annulus to said rear face, enclosure means forming with said rear face a discharge cavity leading to a point of utilization, and spring means between said enclosure means and said rear face whereby said valve part is movable in response to changes in the pressure drop across said orifice.

6. A pump as defined in claim 5 and further characterized by said plunger having a passage formed therein, a ball valve in said passage, a spring loading said ball valve closed and a rod in said passage having one end engaged against said cap and the other end against said ball valve, whereby constant relief pressure is effected.