US2382452A - Fluid pumping mechanism - Google Patents

Description

E; J. sVENsoN FLUID PUMPING MECHANISM Original Filed Aug. 11, 1933 3 Sheets-Sheet l E. J. SVENSON FLUID PUMPING MECHANISM Original Filed Aug. 11 1935 3 Sheets-Sheet 2 Au 14, 1945. E, 4 NS 2,382,452

FLUID PUMPING MECHANISM Original Filed Aug. 11, 1933 3 Sheets-Sheet 3 5.13 U we INVENTOR fluff ffuemiam V Patented Aug. 14, 1945 um'rso STATES PATENT OFFICE 2,382,452 FLUID PUMPING MECHANISM Ernest J. Svenson, Rockford, 11]., aasignor, by mesne assignments, to Odin Corporation, Chb cago, 111., a corporation of Illinois Original application August 11, 1933, Serial No.

her-'16, 1940, Serial No.

17 Claims.

and constitutes an improvement over the struc ture disclosed therein. As set forth on page 1 of my aforesaidpatent, fluid slippage or leakage is a problem with which hydraulic engineers have been confronted. Such fluid slippage or leakage results in greatly reduced efficiency of operation. It is, therefore, one of the important objects of the present invention to provide a pumping mechanism which will overcome the aforesaid and other problems, and to this end the. invention contemplates a novel combination of pumping elements including automatically operable ball check valves in cooperative association with fluid pressure generating elements such as pump plungers.-

More specifically. the inventioncontemplates fluid pumping mechanisms, as set forth above, wherein ball check valves are arranged to function in timed relation with respect to the movement of pressure generating elements such as pump plungers.

It is a further object of the present invention to provide pumping in as set forth above, wherein ball valve means is cooperatively associated with a plurality of shiftable pump plungers which are designed to be mechanically shifted in one direction and hydraulically shifted in the opposite direction.

Another object of the present invention is to provide pumping mechanism which is particulariy adaptable for use in closed hydraulic circuits wherein the fluid returned in the closed circuit to the pump may serve to shift the plun ers in a given direction and wherein fluid slippage Or leakage within the pump is eliminated.

' The foregoing and numerous other objects and advantages will be more apparent from the following detailed description, wherein:

Figure 1 is a transverse sectional view of a variable and relatively slow delivery pumping mechanism of the type contemplated by the present invention, said view being taken substantiall along the line |--i of Figure 3;

is ardivision of my co- Dumps disclosed in my 15- Divided and th is appiicationseptem- 356,896

' tion.

. Figure 2 is a transverse sectional view of said pump taken substantially along the line 2-2 of Figure 1;

Figure 3 is an end elevational view of the pump, shown partly in section, said view being taken substantially along the line 3-4 of Figure 1;

Figure 4 is a fragmentary detail view of the eccentric driving mechanism for the pump structure shown in Figures 1 to 3 inclusive;

Figure 5 is a fragmentary, transverse, sectional view of the eccentric driving mechanism taken substantially, along the line 5-5 of Figure 4;

Figure 6 is a detail sectional view of one of the ball valves disclosing the manner in which said valve serves to control communication between the inlet side of the pump and the pump passageways communicating with the plungers or pistons;

valve of Figure 6 to more clearly illustrate the structural features thereof which render it particularly adaptable for use in closed circuits and the like as illustrated more particularly in Figure 10;

Figure Sis a fragmentary. central, transverse, sectional view of a modified pumping mechanism equipped with ball valves, said view being taken substantially along the line 8-8 of Figure 9 Figure .9 is a view of the right end of the pump structure shown in Figure 8, a portion thereof being broken away along the line 8-9 of Figure 8 to more clearly illustrate the structural arrangement' of the valve mechanisms; and

Figure 10 is a circuit diagram illustrating the manner in which the pumping mechanism of the present invention may be employed in a closed circuit.

Referring now to the drawings, wherein like numerals have been employed to designate similar parts throughout the' various figures, attention is directed to the fact that, for purposes of cleamess and comparison with the disclosure in my aforesaid parent application, the numerals employed herein correspond with the numerals designating like partsin my aforesaid applica- 1 The pump structure shown in the drawings is designated generally by the numeral 18. This pumping mechanism includes a central housing I, which carries a pump driving mechanism designated generally by the numeral I68, an end plate 818. and an oppositely disposed pump housing I12 serving as an enclosure and support for the plunger and valve elements of the pump. Preloaded anti-friction bearlngs I'll provided within the Figure 7 is an enlarged detail view of the ballhousing I88 serve as the support for a rotary driving member or sleeve I18. Longitudinal displacement of the sleeve I18 to the right, Figure 1, is prevented by a clamping ring I18 and an adjusting nut or screw I80, while longitudinal displacement of the sleeve I18 to the left is prevented by a flange III which engages the right preloaded anti-friction bearing I18.

A sleeve I18 carries a driving gear I82 which is adapted to mesh with another gear (not. shown) forming a part of a transmission from a, suitable driving means (not shown). A driving member I88 mounted within and rotatably adjustable with respect to the driving sleeve I18 serves as the means for adjusting the eccentricity of a driving ring I90'. This ring I90 forms the outer race of a radical ball bearing mounted upon an extended stub shaft portion I9I of a cylindrical adjustment member I92. As best seen in Figure 1, the stub shaft portion I 9I is eccentric to the cylindrical adjusting member I92. The member I92 is support ed within a cylindrical recess I92 of the member I18 and is eccentric with respect to said I18. It will, therefore, be clear that the adjustment mechanism is such that rotation of the member I92 within the recess I92 will vary the eccentricity of the stub shaft portion III with respect to the axis of the sleeve I18. In other words, rotatable adjustment of the cylindrical member I92 causes the stub shaftportion I8I to experience eccentric adjustment with respect to the axis of the sleeve I18 which thereby afiects the degree of eccentricity of the driving ring I80. The member I88 has a head portion "811 which is eccentric to the axis of the member I88 and registers within a recess I92a in the member I92. A reduced portion which connects the member I88 with the head I88a passes through a transverse recess or slot I 9211. Thus when it is desired to vary the eccentricity of the driving ring I90, the nut I80 is first loosened and then rotation is imparted to the member I88 by gripping the outer squared end thereof. Rotation of the member I98 causes rotation of the cylindrical member I92 and this results in varying the eccentricity of the stub shaft portion I 9| with respect to the axis of rotation of the sleeve I18 and the member I89. After the required degree of eccentric adjustment has been made, the nut I80 is again tightened- Rotation is imparted to the sleeve I16 and the member I88 by the driving gear I82, and the rin I98 will execute an eccentric motion to a degree which is dependent upon the amount of eccentric adjustment of the stub portion I9I as previously described.

A plurality of fingers I98 are uniformly spaced about the axis of the sleeve I18, and are pivotally supported within the end frame or casing I12 as clearly shown in Figure 2. The free extremities of these fingers are interposed between the driving ring I90 and companion pump pistons or plungers I98. The curvature of the fingers is such as to impart symmetrical acceleration and deceleration of the pistons I98. This feature is fully described in my Patent No. 2,048,524, issued July 21, 1936. Fluid is directed toward and away from the outer ends of the pistons I98 in companion passageways I98, Figures 1 and 3. Each of these passageways I98 communicates with apair of valves, namely an intake control valve designated generally by the numeral 200 andan outlet control valve 282.

Fluid is directed to the valves 288 from an intake conduit 208, Figure 3, which constantly communicates through a transverse passage 288 with an annular passage or port 288. This annular assaaea passage 288 directs fluid to the intake valves 288 through a e 2" which is companioned to each valve. Each of the aforesaid valves 288 includes a ball valve member 2I2, I prefer to employ valve balls comprised of Swedish steel, which has been especially treated to obtain an unusually hard and tough structure. I have found what are well known in the trade as Hultgren Process Brinell balls, to perform very satisfactorily. The balls 2 I 2 are normally urged by means of a coiled spring 2I8, preferably tapered as illustrated in Figure 6, interposed between said balls and a threaded plug 2I8 into engagement with a valve seat 2I8. Referring to Figure 7, wherein I have disclosed an enlarged view of the ball and seat therefor, it will be seen that the seat 2 I 8 is shaped to conform accurately with a portion of the.

spherical surface of the valve ball. By having the springs 2I8 tapered or converging toward the valve ball, as illustrated in Figure 8, the centering of the ball within its seat is materially enhanced.

The ball valve 2I2 is provided with an annular recess 2I8 designed to receive the adjacent portion of the coiled spring 2 I8, Figure 7. The por-' tion of the threaded spring 2 which is received by the annular recess 2 I8, is formed with converging walls which are adapted to abut the companion walls or surfaces of the recess. This arrangement positively prevents the ball from being dislodged and maintains the same surface of the ball in contact with the valve seat 2 at all times.

Attention is also directed to the fact that the annular area 228 presented between the outer periphery of the ball 2I2 and the inner periphery of the valve chamber 222 is less than the crosssectional area presented by the intake passageway 2I0. The significance of this construction will be more apparent when a hydraulic circuit for which the pump mechanism 18 18 particularly adapted, is described. From the foregoing, it will be apparent that fluid from the conduit or pipe line 288 may pass through the valve 208 and into the passageway I98 companion thereto. The intake of the fluid occurs during the inward stroke of the pistons or plungers I88. During the compression stroke of the plungers I98, fluid passes from the passageways I88 into a passageway 2 Illa which communicates with a discharge valve 202. This'valve 282 is similar in structural characteristics to the valve 288 previously described. Each valve 282 includes a ball valve 2I2a, a chamber 222a, and a threaded plug 2I8a. Fluid passing through the valve 282 enters a discharge conduit or pipe line 228.

It will be noted that the spring 2I8a for the valve ball 2I2a is more powerful than the spring for the intake valve ball 2I2, whereby to preclude the opening of the ball of the valve ball 20 when the pistons are being charged. In other words, the valve ball 2I2,a will only open when the piston companion thereto is experiencing its compression stroke, and said valve will not open during any other portion of the cycle under norplication of the feed pump just described, I have illustrated a circuit diagram in Figure 10. This circuit is a portion of the circuit diagram disclosed in my aforesaid parent application with all parts omitted except those necessary to a clear understanding of the operation of the pump. Assume that one of the pistons I96 is experiencing its outward or compression stroke. Fluid under pressure is thereby forced from the space above the piston I86 through the passages I98 and 2I0a and past the valve ball 2I2a into the outlet conduit 224. From the conduit 224, the fluid is conducted into the conduit 306 which is blocked at one end by a control valve designated generally by the numeral 250. A valve member 258 of the control valve mechanism 250 is so positioned as to block one extremity of the conduit 306. The other end of the conduit 306 may be connected through any suitable mechanism designated diagrammatically by a dot and dash line 306a with a conduit 328 which conducts fluid to the right chamber of a hydraulic cylinder I04. This'en-' trance of the fluid into the cylinder I04 causes a piston I to move to the left and displace fluid from the left-hand chamber of the cylinder I04 into a conduit 364 and thence through a conduit 038 which communicates with conduit 204. From conduit 204 fluid passes into the inlet passage 206 of the pump and thence into the annular distributing passage 208 as previously described. The passage 208 communicates with all of the inlet ball valves 200. Fluid will not flow through the valve 200 associated with the piston or pistons moving outward because the fluid pressure in the associated passage I98 is greater than the pressure of the fluid which is being returned to the intake side of the pump. However, as the driving ring I90 moves so as to permit the inward movement of one or more of the plungers I96, the pressure in the passages I98 will decrease, thereby permitting fluid to flow from the passage 208 through companion valves 200 of the receding or inwardly moving plungers and will exert a driving force tending to move the plungers inwardly. From the foregoing description it will be understood that when the pump I6 is connected in the above described closed circuit, fluid within the various conduits moves as a unit, one unit being forced under pressure outwardly through the pump passages 990 and the ball valves 202 and thence to the actuator cylinder m4 and the other unit moving from the discharge side of the actuator cylinder H04 into the intake side of the pump through the ball valves 200 and into the outer extermities of the complementary receding pump plungers.

In the circuit disclosed herein, the presence of the piston rod on one side of the piston i00 creates a differential in working area on opposite sides of the piston. Consequently more fluid is discharged from cylinder I04 than is delivered to said cylinder during the movement thereof to the left, Figure 10. Such excess fluid is free to escape through a small radial passage or vent 349 in the valve member 258. From this vent, 344 the fluid flows through a longitudinal passage 290, a chamber 294, a longitudinal passage 296, a chamber 298 and then through a conduit 300 and a restricted orifice 302 into a reservoir 236. For a more detailed description of the valve mechanism 250, attention is directed to the explanation given in my aforesaid parent application. It is not essential to a clear understanding of the pump mechanism that the valve mechanism 250 be described in more detail. In instances where no differential exists between the areas on the opposite sides of the piston and where the actuator cylinder packings are free from leakage, the bleed'passage 344 may be done away with. or course, in instances where equal size piston rods on both sides of the piston I00 are employed and the discharge volume of the cylinder I04 would be theoretically equal to its intake volume, the bleed passage 344 may still be provided to make up for any leakage past the piston, or packings, that might disturb this theo retical equality. It will, of course, be understood that the bleed passage 344 is very small andis intended only to take care of slight volumetric discrepancies between volumetric deliveryv of the fluid pumpto the actuator and volumetric discharge of fluid from the actuator. It is by no means large enough to carry the full pump volume and does not serve as a means to enable the supercharging of the plunger pump 16 by the rapid traverse or gear pump 226 shown in Figure 10. .In fact, the construction of the pump I6 is such as to preclude the necessity of the supercharging by reason of the absence of fluid slippage or leakage within the pump. a

The ball valves 200 and 202 materially contribute to the eflicient functioning of the pump I6 in circuits of the type shown in Figure 10. I

have operated such pumps over an extended period of time and have foundthat the valve balls stand up underthe severest operating conditions and that theyare adapted for continuous use over an extended period of time without repair or replacement.

Particular attention is directed to the fact that by using the ball valve arrangement in a circuit of the type disclosed herein, the clashing 0f the balls as they seat themselves is positively precluded. This will be more readily appreciated by referring again to Figures-6 and 7, wherein I have shown the balls 2I2 seated by the action of the threaded spring 2I4, Assume now that the pump piston I96, which is companion to the ball, valve shown in Figures 6 and 7, begins to experience an inward movement. This enables fluid from the annular port or passage 208 connected with the discharge side of the actuator cylinder 34 to be delivered to the ball 2I2. This will cause the ball to become unseated and permit fluid to enter the companion passage I90 at a speed which is determined by the speed with which the companion plunger I96 moves inward- 13/. When the plunger reaches the limit of its intake stroke and is about to move in a reverse outward direction, the flow of fluid past the ball 2I2 ceases and'the pressure on the opposite sides of the ball becomes substantially equalized, thereby enabling the ball to gently seat itself at the instant the pump piston I96 begins its compressive stroke. In other words, there is no clashing or violent seating of the ball 2 I2 but, on the contrary, a very gentle seating thereof. The round seat which corresponds to the spherical surface of the ball also contributes toward the effective functioning of the valve. In this connection I again make reference to the fact that the cross-sectional area of the space 220 indicated in Figure 7, is less than the cross-sectional area in the passageway 2 I 0. Thus, a higher speed of fluid takes place within the area 220 than in a the passageway 2I0, thereby enabling the ball 2I2'to be perfectly centered during the opening thereof. Therefore, as the ball gradually moves seats. This should be clearly distinguished from rotary types of valves and others wherein the pressure of the fluid acting upon the valve does not function to urge the valve against the seat.

The importance of the ball valve construction will be more readily apparent when it is understood that in a closed circuit arrangement employed for the' purpose of accurately and uniformly propelling a machine tool, the slightest slippage of fluid past a valve in the pump during the compression stroke of the pump plungers will seriously affect the uniformity of fluid flow. Also, such slippage tends to cause a decided increase in fluid temperature. In fact, one of the most serious problems with which hydraulic engineers have heretofore been confronted is that of temperature increase resulting from the slippage or leakage of fluid along the bearing surfaces of rotary valves. In my above described pumping mechanism. the fluid pressure developed during the compressing stroke of the pump plungers will act upon the intake ball valve so as to positively seal the balls against their respective seats. In the ball check type of pump hereinbefore described, the outlet valve 202 will not open until the'fluid pressure in the passage I98 companion thereto is greater than the pressure in the conduit 224. Therefore,

no back flow from the conduit 224 into the passage m can ever take place. This is'an important advantage which the ball check type of pump presents over pumps in which the control of fluid depends solely upon mechanically actuated valve members. In instances where mechanically actuated valve members are employed, the timed functioning of the valve is controlled mechani-' cally and not in accordance with or in response to predetermined fluid pressure conditions.

In Figures 8 and 9 I have disclosed a modified plunger pump construction designated senerally by the numeral 16b. This pump is similar in many respects to the pump I. previously described, but differs therefrom in providing a tapered rotary valve 558 and a peripheral port I80 which serves to timingly control the flow of fluid toward passages 582. chamber through the conduit 2 which 'c'ommunicates with an end chamber "8. -An antifriction thrust bearing I and clamping r1118 Ill serve to secure the rotary valve against longitudinal movement to the left. Fluid from the chamber I" passes through an internal longitudinal passage 512 which communicates with the valve port "I through radial passages I'll. As the valve port I" sweeps through its. orbit, it

causes fluid to be delivered to the outer ends of the pump pistons Nib during their intake or inward stroke. As the pistons "lb-are moved outwardly, fluid under pressure in the passage- 7 ways I" passes thro h a ball valve I'll and thence into passageways I'll which communicate with the discharge conduit 224.

The tapered arrangement of the rotary "I precludes slippage of fluid toward the larger end of the valvefnamely to the left, Figure 8, and any fluid that may slowly migrate in that direction is received by an annular assage I" which communicates with the intake passage :12

'throushnedia openin m. Asecondannuvalve 19.! valve passage or port I" communicates with a passage "I adopted to be connected with a source of fluid pressure (not shown). For further 2,078,697, particularly Figures 18 and 25 thereof.

The use of fluid pressure at this point serves to insure lubrication and to further counteract any ignated generally by leakage or migration of fluid along the surface of the valve "0 toward the larger end thereof. The valve 558 is driven from a driving mechanism desthe numeral lllb, which is similar in functional istics to themechanism Ill previously described Other types of driving mechanisms may also be employed, see for example the driving mechanism shown in my issued Patent No. 1,989,118 and my copending application, Serial No. 456,670, died May 28, 1930, which will issue into Patent No. 2,215,488 on September 24, 1940.

By employing the ball valves I", I preclude the necessity of using a second port in the valve member Ill similar to the port I". I thus prevent the rotary valve Ill from experiencing fluid pressure which might have s tendency to cause the valve to bind or wear along the peripheral surfaces positioned at each'sidc of the peripheral valve port Ill. while thefiuid pressure from the passageways "2 does exert'itself through the radial passages Ill, provided in the bushing "2, which supports the rotary valve I", this pressure is exerted against a relatively small area of the valve and hence merely serves to counteract the pressure or fluid acting within the peripheral I the present invention contemplates a novel and Fluid enters the pump ball on the high pressure or discharge side of- Y greater than circuit shown in Figure 24 practic pumping structure which is particularly designed for very accurate volumetric delivery of fluid at relatively high pressures. There are environments which require very small volumetric fluid displacement at relatively high pressures. As pointed out in my issued Patent No. 2,140,565, beginning page 9. left column -1 line 65. when a combined body of fluid is subjected to relatively high pressures, the fluid tends to experience a molecular change or compression. In my aforesaid patent I recommend the use of s of said potent when aplunger pump of the type described herein is employed for extremely small fluid displacement under relatively high pressures. Under such conditions the ball check valves disclosed herein function very efllciently and in fact are superior "to conventional rotary valves with which I am familiar; As previously pointed out, the valve the pump will not open unless the pressure of the fluid between the bell and the pump plunger is the pressure of the fluid positioned beyond said ball. This. materially contributes to the eiilcient functioning of the pump under conditions of relatively low displacement and high ressure. I also prefer to construct the housing material associated with the valve balls of a uniform alloy steel treated so that it will wear in conformity with the surface of the boll, although notsshsrdssthebail. Thisenobiesbailstobe usodoveranextendcdperiodoftimewithout and structural character,

requiring replacement. In fact, the longer the ball is used the more perfect becomes the seat in the material associated with the ball. It should also be understood that care must be exercised in properly freezing or otherwise fitting within the pump housing H2 the core or member which carries the ball check valves 200 and 282. There must be a very tight fit between these parts in order to positively prevent fluid leakage along the peripheral surface of this core. The pivoted pump fingers function in cooperation with the ball check valves to increase the eillciency of operation thereof. Not only do these fingers insure symmetry in acceleration and deceleration oi the pump plungers, but they also insure the proper dwell or period oi! inactivity at each end of the plunger stroke and this insures the proper opening and closing of the ball check valves.

The invention is obviously not limited to the specitic structural details disclosed herein, but is capable of other modifications and changes without departing from the spirit and scope of the appended claims. v

- The invention is hereby claimed as follows:

1. In combination with a source of liquid under pressure, a pump including a. plurality of reciprocable plungers, a housing therefor, a driving mechanism for shifting said plungers during their compression stroke only. and limiting the intake stroke thereof, valve means including pressure actuated inlet valve members and pressure actuated outlet valve members preset for operation at different pressures to open and close in timed relation under the pressure control of said plungers, said inlet and outlet valve members being arranged in pairs, each pair companion to one plunger, a common passageway for directing fluid through one member 01 each pair of valve members to the plungers, and a common-passageway for directing fluid through the other-member of each pair of valve members away from said plungers.

2. In combination with a source of liquid under as pressure, a variable displacement pump comprising a fixed casing having an intake passage commuhicating with the source of liquid and a discharge passage, a plurality of cylinders in said casing communicating with each of the passages, a piston reciprocable in each of said cylinders, means for varying the stroke of movement of the pistons within the cylinders comprising means imparting an exhaust stroke only to said pistons and limiting the intake stroke thereof at all dis placements, a pressure actuated valve controlling the communication between the intake passage and each cylinder opening to permit an influx of the liquid from the passage to. the cylinder for imparting an intake stroke to the piston and closing to prevent discharge from the cylinder, and

, an independent pressure actuated valve controlling communication between the discharge passage and each cylinder opening upon an exhaust stroke of the piston and closing upon an intake stroke to prevent return flow into the cylinder.

3. In combination with a source of liquid under pressure, a pumpcomprising a housing having an intake passage communicating with the source of liquid and a discharge passage, a plurality of cylinders in said housing communicating with each of the passages, a plunger reciprocable in each of said cylinders, driving mechanism for imparting an exhaust stroke only to said plungers and limiting the intake stroke thereof, a first pressure actuated valve controlling the communiferential thereacross exceeds a.

cation between'the intake passage and each cylinder opening to permit the influx of the liquid from the passage to the cylinder for imparting an intake stroke to the plunger and closing to permit discharge of liquid from the cylinder, and a second pressure actuated valve controlling communication between the discharge passage and each cylinder opening upon an exhaust stroke of the plunger and closing upon an intake stroke of the plunger to prevent return of flow of liquid into the cylinder, said first pressure actuated valve being constructed to shift to its open position when the liquid pressure differential therea'cross exceeds a. predetermined amount, and the second pressure actuated valve being constructed to open when the liquid pressure diftermined amount.

4. In combination with a source of fluid under pressure, a. pump including a, housing having an intake passage communicating with the source of liquid and a discharge passage, a pluralit of cylinders in said housing communicating with each of the passages, a plunger reciprocable in each of said cylinders, means imparting an exhaust stroke only to said plungers and limiting the intake stroke thereof, pressure actuated means including a valve member controlling the communication between the intake passage and each cylinder opening to permit an influx of the fluid from the passage to the cylinder for imparting an intake stroke to the plunger, said valve means including a spring actuating said valve member to closed position automatically during a reversal of movement of the plunger, and independent pressure actuated valve means including a valve member controlling communication between the discharge passage and each cylinder opening upon an exhaust stroke of the 0 plunger, said last mentioned valve means including a spring actuating said last mentioned valve member to closed position during reversal of movement of .the plunger, the spring of the last mentioned valve means being stronger than the spring of the first mentioned valve means.

. 5. In combination with a source of liquid under pressure, a variable speed, variable displacement pump comprising a casing having an intake passage communicating with the source of liquid and a discharge passage, 2, cylinder in said casing communicating with each of the passages, a piston reciprocable in said cylinder, means for varying the path of travel of the piston within the cylinder comprising means imparting an exhaust stroke only to said piston and limiting the intake stroke thereof at all displacements and speeds, a pressure actuatedinlet valve means including a shifta'ble valve member controlling the communication between the intake passage and the cylinder opening to permit an influx of the liquid from the passage to the cylinder for imparting an intake stroke to the piston. said inlet valve means including a spring actuating said valve member to closed position to prevent discharge from the cylinder, the force of said spring being such in relation to the pressure of the source as to permit the liquid from .the source to maintain the inlet valve member in open position during the entire intake stroke of the plunger at all speeds and displacements, and Spring controlled pressure actuated outlet valve means controlling communication between the discharge passage and the cylinder opening upon an exhaust stroke of the piston and closing upon an intake stroke to prevent return flow into the cylinder,

greater predesaid inlet valve being preset to open at a lower pressure diflerentlal than the outlet valve.

6. In combination with a source of liquid under stroke only to said piston and limiting the intake I stroke thereof at all displacements, an inlet valve controlling the communication between the intake passage and the cylinder opening to permit.

an influx of the liquid from the passage to the cylinder for imparting an intake stroke to the piston and closing to prevent discharge from the cylinder, and an independent pressure actuated outlet valve controlling communication between the discharge passage and the cylinder opening upon an exhaust stroke of the piston and closing upon an intake stroke to prevent return flow into the cylinder, said inlet and outlet valves being preset to open at'difl'erent predetermined operating pressures.

7. A variable displacement pump for use in a closed fluid circuit comprising a casing having an intake passage and a discharge passage, a plurality of cylinders in said casing communicating with each of the passages to receive liquid at a predetermined pressure and to discharge liquid reciprocable in each of said cylinders, means for varying the path of travel oi the pistons within the cylinders comprising means impart ng an exhaust stroke only to each of said pistons and limiting the intake stroke of each piston at all displacements, pressure actuated spring controlled inlet valve means controlling the communication between the intake passage and each cylinder opening to permit an influx of the liquid from the passage to the cylinder at said predetermined pressure for imparting an intake stroke to the piston and closing upon completion of the intake stroke to prevent discharge from the cylinder, and a second pressure actuated outlet valve means including a shittable valve member controlling communication between the discharge passage and each cylinder, said second pressure actuated outlet valve means including a spring urging said valve member to closed position and constructed to permit movement of the valve member to open position only at a pres- Y sure above the pressure of the liquid in the discharge passage and to close upon completion of the exhaust stroke 01' the piston to prevent return flow of liquid into the cylinder during the intake stroke, said outlet valve being present to open at a higher differential operating pressure than said inlet valve.

8. In combination with assume of liquid under pressure, a variable displacement pump comprising a casing having an intake passage communieating with the source of liquid and a discharge passage, a plurality ofradially disposedcylinders in said casing communicating with each of the interposed between said eccentric driving memher and said pistons, vsaid driving member and followers being constructed to operate said piston in definite timed relation for all displacements, pressure actuated inlet valves controlling the communication between the intake passage and the cylinders opening in said timed relation for intervals determined by the displacement of the pistons to permit an influx of liquid from the passage to the cylinders for imparting intake strokes to the piston and closing in said timed relation to prevent discharge from the cylinders, and independent pressure actuated outlet valves controlling communication between the discharge 'passage and the cylinders opening in said timed relation for intervals determined by the cla placement of the pistons in their exhaust strokes to discharge liquid from the cylinders and closing in said timed relation upon the completion of the exhaust strokes to prevent return flow into the cylinders during the intake strokes, said outlet valves being preset to open with a higher diflerential pressure than the inlet valves.-

9. In combination with a source of liquid under pressure, a pump including a housing having intake and discharge passages and a plurality ot plunger accommodating bores, a reciprocable plunger asociated with each bore, driving mechanism for shifting said plungers in one direction and limiting their movement in the opposite direction, said plungers being adapted to be 1 shifted in said opposite direction by liquid presfrom said cylinders at a higher pressure, a piston sure, pressure actuated inlet valves operable at a given pressure for controlling the flow oi liquid to each bore from said source through said intake passage, and independent pressure actuated outlet valves operable only at a pressure greater than said given pressure for controlling the flow-o! fluid from each bore to said discharge e in timed relationwith the flow of fluid to each bore from said intake passage.

10. A pump adapted for use in a closed fluid circuit wherein fluid under pressure is delivered to an actuator and fluid discharged from said actuator is returned under pressure to the intake side of the pump, including a housing having aplurality of cylinders, a reciprocable plunger in each cylinder, a rotary eccentric driving mechanism for imparting an exhaust stroke only to said plungers, fluid pressure imparting an intake stroke to said plungers, means for limiting the intake stroke of said plungers, valve means for controlling the flow of fluid toward and away from said plungers including a pressure actuated inlet ball valve for each plunger, and a pressure actuated outlet .ball valve for each plunger and operable to open position only at a pressure higher than the pressure required to open the inlet ball valve, fluid inlet channel means communicating with all of said inlet ball valves,

and outlet channel means communicating with all of said outlet ball valves.

11. In a pimp structure, a housing, a plurality of cylinders formed in said housing, a piston reciprocable in each cylinder, means for importing progressively increasing and decreasing speeds of movement to the pistons during the reciprocation thereof, a chamber in the housing, means for varying the strokes of the pistons within the cylinders, and pressure actuated valve means for each of said cylinders comprising a passage formim a reduced extension of said chamber. said passage and chamber being in fluid communication with the cylinder, a hardened metal valve ball disposed in the chamber, a valve seatformedatthejtmcturebetweensaidcham-' her and said passage, and a spring for urging the ball against said seat whereby to close said passage, the ball being surrounded by an annular space within the chamber which is less in crosssectional area than the cross-sectional area of the passage, whereby to insure a greater fluid velocity through said annular space than through said passage to effect the centering of the valve ball with respect to its seat.

12. In a pump structure, a housing, a plurality of cylinders formed in said housing, a piston reciprocable in each cylinder, means for imparting progressively increasing and decreasing speeds of movement to the pistons during the reciprocation thereof, means for varying the strokes of the pistons within the cylinders, and pressure actuated valve means for each of said cylinders comprising a chamber in the housing, a passage forming a reduced extension of said chamber, said passage, and chamber bein in fluid communication with the cylinder, a hardened metal valve ball disposed in the chamber, a valve seat formed at the juncture between said chamber and said passage, 'a spring for urging the ball against said seat whereby to close said passage, means for holding the spring in predetermined position, and means interlocking a portion of the spring with the ball whereby to hold the ball in predetermined position with respect to its seat during its opening and closing movements, so as to insure the continuous presenta- 13. In a pump structure, a housing, a plurality of cylinders formed in said housing, a piston reciprocable in each cylinder, means for imparting progressively increasing and decreasing speeds of movement to the pistons during the reciprocation thereof, means for varying the strokes of the pistons within the cylinders, and pressure actuated valve means for each of said cylinders comprising a chamber in the housing, a passage forming a reduced extension of said chamber, said passage and chamber being in fluid communication with the cylinder, a hardened metal valve ball disposed in the chamber, a valve seat formed at the juncture between said chamber and said passage, 9. spring for urging the ball against said seat whereby to close said passage, means for holding the spring in predetermined position, and means comprising an annular recess formed on the valve ball interlocking a portion of the spring with the ball whereby to hold the ball in predetermined position with respect to its seat during its opening and closing'movements, so as to insure the continuous presentation of the same portion of the ball into engagement with its seat.

14. In a pump structure, a housing, a plurality of cylinders formed insaid housing, a piston reciprocable in each cylinder, means for imparting progressively increasing and decreasing speeds of movement to the piston during the reciprocation thereof, means for varying the strokes of the pistons within thecylinders, and pressure .actuated valve means for each of said cylinders comprising a chamber in the housing, a passage forming a reduced extension of said chamber, said passageand chamber being in fluid communication with the cylinder, a' hardened metal valve ball disposed in the chamber, a valve seat formed at the juncture between said chamberandsaidpassagaaspringforurgimthe ballagainstsaidseatwherebytocloeesaidpassage, means holding the spring in predetermined position, means interlocking a portion ottbe tion of the same portion of the ball into engagement with its seat.

spring with the valve ball whereby to insure the presentation of the same portion of the valve ball against its seat during operation of the ball, and .the ball being surrounded by, an annular space withinv the chamber. which is less in crosssectional area than the cross-sectional area of the passage, whereby to effect a fluid centering of the valve ball in respect to its seat.

15. In a pump structure, a housing, a plurality of cylinders formed in said housing, a piston reciprocable in each cylinder, means for imparting progressively increasing and decreasing speeds of movement to the pistons during the reciprocation thereof, means for varying the strokes of the pistons within the cylinders, and pressure actuated valve means for each of said cylinders comprising a chamber in the housing, a passage forming a reduced extension of said chamber, said passage and chamber being in fluid communication with the-cylinder, a hardened metal valve ball disposed in the chamber, a valve seat formed at the juncture between said chamber and said passage, said valve seat having a spherical surface for cooperative engagement with the ball, and said seat being of less hardness than the ball, and a spring for urging the ball against said seat whereby to close said passage.

16. In a pump structure, a housing, a plurality of cylinders formed in said housing, a piston reciprocable in each cylinder, means for imparting progressively increasing and decreasing speeds of movement to the pistons during the reciprocation thereof, means for varying the strokes of the pistons within the cylinders, and pressure actuated valve meansfor each of said cylinders comprising a chamber in the housing, a passage forming a reduced extension of said chamber, said passage and chamber being in o fluid communication with the cylinder, 9. hardened metal valve ball disposed in the chamber,

a spherical valve seat formed at the juncture between said chamber and said passage, said valve seat being of less hardness than the valve ball, and a spring for urging the ball against said seat whereby to close said passage, the ball being sunounded by an annular space within the chamber which is less in cross-sectional area than the cross-sectional area of the passage, whereby to efiect the fluid centering of the valve ball with respect to its seat.

17. In a pump structure, a housing, a plurality of cylinders formed in said housing, a piston reciprocable in each cylinder, means for imparting progressively increasing and decreasing speeds of movement to the pistons during the reciprocation thereof, means for varying the strokes of the pistons within the cylinders, and pressure actuated valve means for each of said cylinders comprising a chamber in the housing, a passage forming a redimed extension 01 said chamber,

said passage and chamber-being in fluid communication with the cylinder, a hardened metal valve ball disposed in the chamber, a spherical close said passage, means for holding the spring in position, and means interlocking a portion of thespringwiththevalveballwherebytoinsm-e the presentation 01' thesame ball sin-race said seat during operation of the valve.

mesa-J. SVINBON.

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