US3007415A

US3007415A - Self-regulating reciprocating action pumps, and in particular in fuel injection pumps

Info

Publication number: US3007415A
Application number: US779651A
Authority: US
Inventors: Bessiere Pierre Etienne
Original assignee: Individual
Current assignee: Individual
Priority date: 1957-12-18
Filing date: 1958-12-11
Publication date: 1961-11-07
Anticipated expiration: 1978-11-07
Also published as: FR1195334A; CH351442A

Description

P. E. BESSIERE Nov. 7, 1961 3,007,415 SELF-REGULATING RECIPROCATING ACTION PUMPS, AND IN PARTICULAR IN FUEL INJECTION PUMPS 2 Sheets-Sheet 1 Filed Dec. 11, 1958 E a X I CNN wwuuuuu mp V MNP Nov. 7, 1961 P. E. BESSIERE 3,007,415

SELF-REGULATING RECIPROCATING ACTIQN PUMPS, AND

IN PARTICULAR IN FUEL INJECTION PUMPS 2 Sheets-Sheet 2 Filed Dec. 11, 1958 AI/ A /NVENTOR Pier-'1 ET,nn:. Bess-er: BY 5 M1- 5 Avm /veys .Fi/J 4 United States Patent SELF-REGULATWG RECIPRQQATING ACTION PUMPS, AND IN PARTICULAR IN FUEL IN- JECTION PUD/ES Pierre Etienne Bessiere, 55 Bid. Commandant Charcot,

Neuilly-sur-Seine (Seine Department), France Filed Dec. 11, 1958, Ser. No. 779,651 Claims priority, application France Dec. 1S, 1957 v 11 (Zlaims. (Cl. 103--38) The present invention relates to self-regulating reciprocating action pumps, that is to say to pumps in which the active element (piston, diaphragm or the like) has a reciprocating movement and the delivery rate is regulated automatically as a function of the speed at which this pump is driven, that is to say of the number of reciprocations per unit of time of the pump piston. This invention is more especially but not exclusively concerned with fuel injection pumps for internal combustion engines.

It has already been proposed, concerning reciprocating pumps of this kind (see U.S. patent application Serial No. 90,984, filed February 23, 1961, for Improvements in Reciprocating Liquid Pumps, and in Particular in Fuel Injection Engines as a continuation-in-part of application Serial No. 673,343, filed July 22, 1957, for Improvements in Reciprocating Liquid Pumps, and in Particular in Fuel Injection Pumps, now abandoned) to make use of a movable member called shuttle which is displaced by the pressure of the liquid delivered by the pump piston during its delivery strokes against a return force, produced for instance by a spring, and which is braked during its return movements, which take place during the suction strokes (return strokes) of the pump piston, the braking effect being such that, for speeds exceeding a given value of the pump speed, said shuttle has a return stroke which is the shorter as the speed of the engine is higher, this reduction of the return strokes producing an automatic regulation of the flow rate of the liquid delivered by the pump. 1

Up to the present time, braking of the return movement of the shuttle was generally obtained by means of a throttled passage or section provided in a conduit through which the shuttle drives, during every return stroke thereof, the liquid which had precedingly produced its movements in the other direction.

The object of the present invention is to provide a pump of the kind above described which is better adapted to meet the various requirements of practice.

For this purpose, I provide two distinct fluid circuits, one being for the liquid which produces the movements of the shuttle in one direction under the action of the pump piston during the delivery stroke thereof, and the other for a fluid which exerts upon the shuttle a braking effect during the return stroke thereof.

This separation of the circuits permits for instance of using, for the production of the braking effect, a fluid the viscosity of which corresponds particularly well to said effect and/or of placing the fluid in this circuit under a suitable pressure.

Preferred embodiments of the present invention will be hereinafter described with reference to the accompanying drawings, given merely by way of example and in which:

FIG. 1 is a diagrammatic vertical sectional view of a fuel injection pump made according to the present invention.

FIGS. 2 and 3 are similar views corresponding to modifications.

The pump includes a piston 1 working in a first cylinder 2 provided with a liquid inlet conduit 3 which is closed by piston 1 during its upward (delivery) stroke, said piston being driven through any suitable means. For instance, the piston may be driven by a cam, itself 3,001,415 Patented Nov. 7, 1961 actuated by the engine on which the pump is mounted when said pump is a fuel injection pump so that the number of reciprocations of piston 1 per unit of time corresponds to the number of revolutions of the engine.

When the pump is a fuel injection pump, the liquid entering cylinder 2 through inlet port 3 is the fuel to be delivered by the pump. Cylinder 2 is in communication with a second cylinder 4 in which works an auxiliary piston, called, shuttle piston 5. On one of its sides, said shuttle piston 5 is subjected, as soon as port 3 has been closed, to the pressure of the liquid delivered by piston 1, whereas the other side of shuttle piston 5 is subjected to the action of a return spring 6. Under the action of this spring, shuttle piston S is urged downwardly so as to apply its under end face against a shoulder 7 provided at the lower end of cylinder 4.

A discharge conduit 8 starts from a point of the wall of cylinder 4 located at some distance above shoulder 7. As soon as the opening of this conduit 8 is cleared by shuttle piston 5, the upward movement of said shuttle piston under the effect of the liquid delivered by piston 1 stops and the excess of liquid delivered by piston 1 then passes directly to the outside through said discharge conduit 8. The position'of said conduit 8 therefore determines the uppermost position of shuttle 5 in cylinder 4.

Shuttle 5 is connected, by a rod 9 which slides in a fluidtight fashion through the upper end 10 of cylinder 4, to a second auxiliary piston 11 working in a cylinder 12. This cylinder 12 is thus divided by piston 11 into two

spaces

12a and 12b. Space 12w constitutes, with the upper face of piston 11, the portion of the pump from which fuel is delivered, through a delivery conduit 13 provided with a check-valve 14, toward the injector or injectors to be fed with fuel by the pump. In order to supply space 12a with fuel to be delivered by the pump, said space is connected for instance with a feed conduit 15 provided with a check-valve 16 and starting from, a primary pump'of conventional type. If the liquid introduced into cylinder 2 and which serves to the hydraulic control of shuttle 5 is constituted by the fuel which is to be delivered from the space 12a of cylinder 12, the feed conduits of both cylinders 2 and 15 may be fed from the same primary pump.

The space 1211 of cylinder 12 which is formed between the bottom part of the piston 11 and the surrounding portion of the casing, this portion being integral with and therefore fixed with respect to the second cylinder, contains the liquid serving to brake, when piston 1 is moving downwardly, the downward movement of piston 11 rigid with shuttle piston 5. For this purpose,

space 12b is provided on the one hand with a feedconduit 17 having a check-valve 18 mounted therein, and on the other hand with a discharge conduit 19 provided with a throttled passage 20 the cross-section area of which is advanatgeously adjustable, for instance by means of a screw 21. Conduit 17 is connected with a pump 22, for instance a rotary pump such as a gear pump, which is preferably driven by the engine or by a machine the speed of which is proportional to that of the engine, this pump constantly conveying braking liquid to space 12b;

A discharge conduit 23 branches out from conduit 17 at a point thereof upstream of check-valve 18. This conduit 23 contains a safety valve 24 which is urged by a spring 25 toward the position in which it closes conduit 23, the compression of this spring being adjustable by means of a screw 26.

When screw 26 is unscrewed as much as possible, the force exerted by spring 25 on safety valve 24 is small but very slightly higher than the force of the spring of check-valve 18, so that the pressure of the fluid present in space 12b, the maximum value of which pressure is determined by the force of spring 25, is also small. This maximum pressure may however be increased when spring 25 is more and more compressed by rotation of the adjustment screw 26.

Preferably, I further provide a locking screw 27 for safety valve 24 so that said valve may be secured in the position shown by FIG. 1 where this valve closes conduit 23.

The operation of the pump shown by FIG. 1 is as follows:

Let it be supposed first that screw 27 is in the position which releases safety valve 24 and that screw 26 is in the position which corresponds to the lowest possible compression of spring 25.

For speeds of pump 1, 2 lower than a given value (that is to say for speeds of the engine fitted with the fuel injection pump lower than a given value), the braking exerted by the fluid present in space 12b and which is discharged to the outside past the throttled passage (the pressure of this liquid being practically constant and never exceeding that determined by spring does not prevent the parts 5, 9, 11 from moving down under the effect of spring 6 in cylinders 12 and 4 until shuttle 5 is applied against shoulder 7. The suction stroke of piston 11 in cylinder 12 is therefore maximum and the amount of fuel delivered past check-valve 14 into delivery conduit 13 is also maximum. But when the speed of piston 1 exceeds a given value, the braking action exerted by the fluid in space 12b brakes the downward movement of the system 5, 9, 11 to such a degree that piston 1 begins a new upward stroke before shuttle 5 has reached shoulder 7. The suction stroke of piston 11 is therefore shortened due to the formation of what may be considered as a liquid abutment under shuttle 5. This shortening of the strokes is the more important as the speed at which the pump is driven increases and I thus obtain the liquid abutment self-regulation already described in the above mentioned patent application. Adjustrnent of the cross-section of the throttled passage 20 makes it possible to vary the value of the speed above which the liquid abutment starts having its effect.

If, now, screw 26 is tightened so as to compress the spring 25, the pressure in space 12b may reach values up to a higher maximum. The braking effect exerted by the fluid in space 12b.is thus reinforced and the liquid abutment starts being formed for lower values of the speed of piston 1.

For high values of the compression of spring 25, and also when the safety valve 24 is secured upon its seat by means of screw 27, the speed at which pump 22 is driven constitutes another factor which influences the self-regulation effect obtained by means of the liquid abutment. This is due to the fact that the pressure of the fluid in space 12b is then the higher as the speed of pump 22 is itself higher. If pump 22 is driven at a speed equal or proportional to that of the engine, the pressure in space 12b then depends upon this speed. If the crosssection of the throttled passage 20 is constant and if safety valve 24 is secured in the position where it closes conduit 23, the pressure varies as the square of the speed of pump 22. In such conditions, a given increase of the speed of pump 22 may cause the pressure of the fluid in space 12b to become suflicient to balance the return force exerted on shuttle piston 5 when this piston is in the position where it opens discharge conduit 8. The shuttle piston and therefore piston 11 will then remain, despite the downward movements of piston 1, in their upper position and any injection of fuel is stopped. The speed for which this takes place is therefore a top speed which can never be exceeded by the engine.

, The value of this top speed obviously depends upon the cross'section area of throttled passage 20. It is therefore possible to modify the value of this top speed by varying the adjustment of said throttled passage. I thus obtain a regulation of the all speeds type.

Other means for varying the self-regulation effect in the pumps of the type above described might consist in controlling the position of screw 21 or of any other means for determining the cross-section area of throttled passage 20 by means of a governor, itself operative as a function of the speed or any other regulation factor. When the throttled passage 20 is controlled as a function of the speed, it is possible to obtain either a reduction or an increase of the cross-section area of the throttled passage. In the case of an increase, it is for instance possible to obtain a constant fineness of the regulation for all speeds.

In order to vary the position of screw 21 as a function of the speed, I may make use of a regulating device including another pump analogous to pump 22 and driven as a function of the speed, this pump creating a pressure which is also a function of the speed, which would be used for moving the screw, for instance by means of a rack carried by a piston subjected to this pressure. I may also replace screw 21 by one of the devices described in the French patent application Ser. No. 742,761, filed by me on July 8, 1957, for Improvements Brought to Hydraulic Speed Governors, in Particular for Fuel Injection Pumps. I might also provide means for automatically controlling screw 26.

The pump shown by FIG. 2 differs from that shown by FIG. 1 only by the means for feeding liquid to the space 12a of cylinder 12. In the construction of FIG. 2, I make use of the liquid delivered by shuttle piston 5 during its downward stroke for feeding this liquid to space 12a. For this purpose, space 12a is connected with the lower chamber of cylinder 4 by means of a conduit 28 controlled by a slide valve 29. Furthermore, in the passage 30 through which cylinder 1 communicates with cylinder 4, there is provided a check-valve 31 opening in the direction for which the liquid can flow from cylinder 2 to cylinder 4.

Slide valve 29 is provided with a transverse passage 32 for the flow of the liquid, and said slide valve is controlled by the liquid placed under pressure in cylinder 2. For this purpose, cylinder 33 in which slide valve 29 is movable is connected, through a conduit 34, with cylinder 2. Furthermore, a return spring 35 acts upon slide valve 29 to tend to apply it against a shoulder 36 located at a level such that, when slide valve 29 is on said shoulder, passage 32 is in line with conduit 28 and therefore opens this conduit. On the contrary, as soon as piston 1, during its upward stroke, sends liquid under pressure from cylinder 2 to the under face of slide valve 29, thus causing an abutment 37 carried by said valve to come into contact with the top end of cylinder 33, conduit 28 is closed.

'In' order to obtain that conduit 28 is closed before piston 1 delivers fuel into cylinder 4, check-valve 31 is provided with a spring the strength of which is greater than that of spring 35 acting upon slide valve 29. Thus, slide valve '29 closes conduit 28 as soon as piston '1 starts upon its upward stroke, and practically the whole of the liquid delivered by'piston 1 flows, past check-valve 31, into cylinder 4 without being able to escape, through conduit 28, to the space 12a of cylinder 12. On the contrary, as soon as piston '1 starts upon its downward stroke, conduit 28 is opened and the liquid located under shuttle piston 5 in cylinder 4 is transferred from this cylinder into the space 12a of cylinder 12. This transfer is effected without any braking action being exerted upon the liquid flowing through conduit 28.

Of course, in the embodiment of FIG. 2, the liquid delivered by piston 1 must be constituted by the fluid to be delivered from space 12a through conduit 13. Furthermore it should be noted that, in the device of FIG. 2, the diameters of shuttle piston 5 and piston 11 must preferably have the same value or anyway the diameter of piston 11 should be greater than the diameter of piston 5, whereas this condition is not necessary in the case of a pump made according to FIG. 1.

The operation of the pump according to FIG. 2 is quite analogous to that of the pump shown by FIG. 1.

FIG. 3 shows another modification of a pump made according to the invention.

According to FIG. 3, the fluid which is to brake the downward movement of shuttle piston a is caused to flow through a distinct cylinder 38 located for instance laterally with respect to cylinder 2 (in which works piston 1) and to cylinder 4a (in which works shuttle piston 5a). In this case the upper chamber of cylinder 4a where return spring 6 is located may be used as a delivery chamber 120 on which starts the delivery conduit 13. In the construction illustrated by FIG. 3, the feed .of fuel to said delivery chamber 12c has been shown as similar to that illustrated on FIG. 1 relatively to chamber 12a.

Concerning the braking means provided in cylinder 38, it is constituted by a piston 39 connected to shuttle piston 5a, for instance by a lever 40. The braking fluid inlet conduit 17a opens into the upper chamber 38a of cylinder 38, this fluid being delivered by a rotary pump 22 analogous to the rotary pumps 22 already described with reference to the preceding embodiments. Furthermore, a discharge conduit U, which starts from said chamber 38a, is provided with a throttled passage 20 preferably adjustable by a screw 21. Piston 39 is advantageously placed under the action of a return spring 41 disposed in the lower chamber of cylinder 38, this chamber being provided with a hole 42 opening to the outside. However, the provision of spring 41 is not absolutely necessary in view of the mechanical connection between shuttle piston 5a and piston 39. r Y

The operation of the pump illustrated by FIG. 3 is quite analogous to that of the pumps shown by PIGS. 1 and 2. When piston 1 is moving upwardly, it causes shuttle piston 5a to move upwardly in its cylinder 4a, so as to deliver liquid from space 120 into delivery conduit 13. The movement of shuttle piston 5a stops when it clears the discharge conduit 8 starting from cylinder 4a. As soon as piston 1 starts moving downwardly, shuttle piston 5a also begins to move downwardly. However, this return movement is now braked by the action exerted by the braking fluid in chamber 38a upon piston Of course/the arrangement shown by FIG. 3 may be completed by the provision of adjusting means acting upon screw 21 and/or upon screw 26 as above described with reference to the pump shown by FIG. 1.

In a general manner, while I have, in the above description, disclosed what I deem to be practical and ethcient embodiments of my invention, it should be well understood that I do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present invention as comprehended Within the scope of the accompanying claims.

What I claim is: a

1. A pump which comprises, in combination, a first cylinder, a first piston fitting slidably in said cylinder and having a reciprocating movement therein, a second cylinder fixed in position with respect to said first cylinder, a shuttle piston fitting slidably in said second cylinder for reciprocating therein, hydraulic means for operatively connecting said shuttle piston with said first piston, so that said first piston, on every compression stroke thereof, causes said shuttle piston to move in a corresponding direction in said second cylinder, a liquid feed and delivery circuit, pump means operatively connected with said shuttle piston and in communication with said circuit for delivering liquid therethrough in response to every movement of said shuttle piston in said direction, a circuit connected with said first cylinder for the Operation of said hydraulic means, resilient means interposed between said shuttle piston and said second cylinder for constantly urging said shuttle piston in a direction opposed to said first mentioned direction, a third liquid circuit distinct from said two above mentioned circuits, cooperating means, one operatively connected with said shuttle piston and the other fixed with respect to said second cylinder, said cooperating means forming between themselves a chamber the volume of which varies in response to reciprocation of said shuttle piston and which forms a part of said third circuit, means belonging to said third circuit and adapted to communicate therewith to force liquid into said chamber during the periods of expansion thereof, outlet conduit means belonging to said third circuit and adapted to communicate with said chamber to constitute the outflow therefrom during the periods of retraction thereof, and means for throttling a portion of said outlet conduit means to brake the movement of said shuttle piston in said second mentioned direction.

2. A pump which comprises, in combination, a first cylinder, a first piston fitting slidably in said cylinder and having a reciprocating movement therein, a second cylinder fixed in position with respect tosaid first cylinder, a shuttle piston fitting slidably in said second cylinder for reciprocating therein, hydraulic means for operatively connecting said shuttle piston with said first piston, so that said first piston, on every compression stroke thereof, causes said shuttle piston to "move in a corresponding direction in said second cylinder, a liquid feed and delivery circuit, pump means operatively connected with said shuttle piston and in communication with said circuit for delivering liquid therethrough'in response to every movement of said shuttle piston in said direction, a circuit connected with said first cylinder for the operation of said hydraulic means, resilient means interposed between said shuttle piston and said second cylinder for constantly urging said shuttle piston in a direction opposed to said first mentioned direction, a third liquid circuit distinct from said two above mentioned circuits, cooperating means, one operatively connected with said shuttle piston and the other fixed with respect to said, second cylinder, said cooperating means forming between themselves a chamber the volume of which varies in response to reciprocation of said shuttle piston and which forms a part of said third circuit, said third circuit including anportion upstreamof said variable volume chamber and a discharge portion downstream thereof, an auxiliary pump having a delivery flow rate proportional to its speed of operation mounted in said upstream portion of said third circuit to feed liquid thereto toward said variable volume chamber, said pump being driven at a speed proportional to the speed of reciprocation of said. first piston, and means for throttling said discharge portion of said third circuit to brake the movement of said shuttle piston in said second mentioned direction.

3. A pump which comprises, in combination, a first cylinder, 9, first piston fitting slidably in said cylinder and having a reciprocating movement therein, a second cylinder fixed inposition with respect to said first cylinder, a shuttle piston fitting slidably in said second cylinder for reciprocating therein, hydraulic means for operatively connecting said shuttle piston with said first piston, so that said first piston, on every compression stroke thereof, causes said shuttle piston to move in a corresponding direction in said second cylinder, a liquid delivery circuit, pump means operatively connected with said shuttle piston'and in communication with said circuit for delivering liquid therethrough in response to every movement of said shuttle piston in said direction, a circuit connected with said first cylinder for the operation of said hydraulic means, resilient means interposed between said shuttle piston and said second cylinder for constantly urging said shuttle piston in a direction opposed to said first mentioned direction, a third liquid circuit distinct from said two above mentioned circuits, cooperating means, one opera atively connected with said shuttle piston and the other fixed with respect to said second cylinder, said cooperating means forming between themselves a chamber the volume of which varies in response to reciprocation of said shuttle piston and which forms a part of said third circuit, said third circuit including a portion upstream of said variable volume chamberand a discharge portion downstream thereof, an auxiliary pump having a delivery flow rate proportional to its speed of operation mounted in said upstream portion of said third circuit to feed liquid thereto toward said variable volume chamber, said pump being driven at a speed proportional to the speed of reciprocation of said first piston, means for throttling said discharge portion of said third circuit to brake the movement of said shuttle piston in said second mentioned direction, and a check-valve inserted in said third circuit between said auxiliary pump and said variable volume chamber, said check-valve opening toward said variable volume chamber.

4. A pump which comprises, in combination, a first cylinder, a first piston fitting slidably in said cylinder and having a reciprocating movement therein, a second cylinder fixed in position with respect to said first cylinder, a shuttle piston fitting slidably in said second cylinder for reciprocating therein, hydraulic means for operatively connecting said shuttle piston with said first piston, so that said first piston, on every compression stroke thereof, causes said shuttle piston to move in a corresponding direction in said second cylinder, a liquid delivery circuit, pump means operatively connected with said shuttle piston and in communication with said circuit for delivering liquid therethrough in response to every movement of said shuttle piston in said direction, a circuit connected with said first cylinder for the operation of said hydraulic means, resilient means interposed between said shuttle piston and said second cylinder for constantly urging said shuttle piston in a direction opposed to said first mentioned direction, a third liquid circuit distinct from said two above mentioned circuits, cooperating means, one operatively connected with said shuttle piston and the other fixed with respect to said second cylinder, said cooperating, means forming between themselves a chamber the volume of which varies in response to reciprocation of said shuttle piston and which forms a part of said third circuit, said third circuit including a portion upstream of said variable volume chamber and a discharge portion downstream thereof, an auxiliary pump having a delivery flow rate proportional to its speed of operation mounted in said upstream portion of said third circuit to feed liquid thereto toward said variable volume chamber, said pump being driven at a speed proportional to the speed of reciprocation of said first piston, means for throttling said discharge portion of said third circuit to brake the movement of said shuttle piston in said second mentioned direction, a check-valve inserted in said third circuit between said auxiliary pump and said variable volume chamber, said check-valve opening toward said variable volume chamber, a branch conduit leading from a part of said third circuit located between said auxiliary pump and said check-valve, and a safety valve inserted in said branch conduit so as yieldingly to oppose the outflow of liquid therethrough, said safety valve including spring means mounted to oppose opening thereof.

5. A pump according to claim 4 in which said spring means is adjustable.

6. A pump according to claim 4 further including means for securing said safety valve in the branch conduit closing position.

7. A pump according to claim 2 in which said throttling means is adjustable.

.8. A pump which comprises, in combination, a first cylinder, a first piston fitting slidably in said cylinder and having a reciprocating movement therein, a second cylinder mounted in fixed position with respect to said first cylinder, a shuttle piston fitting slidably in said second cylinder for reciprocation therein, said shuttle piston dividing said second cylinder into two chambers, a passage forming a communication between one of said chambers and one end of said first cylinder, the Wall of said first cylinder being provided with a liquid inlet port and the wall of said second cylinder being provided with a discharge port, whereby movement of said first piston toward said end of said first cylinder causes said shuttle piston to be moved in the direction which causes the volume of said last mentioned chamber to increase, spring means in the other of said chambers between said shuttle piston and said second cylinder urging said shuttle piston to move in the direction which causes the volume of said last mentioned chamber to increase, a third cylinder in line with said second cylinder and separated therefrom by anend wall, a third piston fitting slidably in said third cylinder for reciprocation therein, said end wall being provided with a cylindrical hole extending in the longitudinal direction of said second and third cylinders, a rod fitting slidably in said hole, the portion of said rod that projects into said second cylinder carrying said shuttle piston rigidly fixed thereto, the portion of said rod that projects into said third cylinder carrying said third piston rigidly fixed thereto, said third piston dividing said third cylinder into two spaces, a first one adjoining said end wall and a second one on the other side of said third piston, the end of said third piston that is adjoining said end wall being provided with an inlet port and a discharge port, means for feeding liquid under pressure to said last mentioned inlet port, a discharge conduit leading out from said discharge port, means for throttling a portion of said discharge conduit, a delivery conduit leading out from said second space and means for feeding liquid to said second space during the strokes of said third piston for which the volume of said second space is increasing.

9. A pump according to claim 8 in which the last mentioned means include a feed conduit opening into said second space and a check-valve in said last mentioned conduit opening into said second space.

10. A pump according to claim 8 in which the last mentioned means include a by-pass conduit opening at one end into said second space and at the other end into said first mentioned chamber near the end thereof into which opens said passage, a check-valve in said passage opening only toward said last mentioned chamber, and means in said by-pass conduit operative in response to the movements of said first cylinder for cutting the communication between said ends of said bypass conduit during the movements of said first piston toward said end of said first cylinder and opening said communication during the movements of said first piston in the opposed direction.

11. A pump according to claim 1 in which said means forming between them a chamber of varying volume include a third cylinder parallel to and at a distance from said first and second cylinders but having a fixed position with respect thereto, and a piston fitting slidably in said third cylinder to form said variable volume chamber therewith, and lever means between said shuttle piston and said third mentioned piston for moving said third piston in said third cylinder in response to the movements of said shuttle piston in said second cylinder.

Outin Apr. 28, 1942 Garday et a1. Nov. 21, 1950