US1938403A - Fuel pump - Google Patents

Description

Dec. 5, 1933.

E. A. ROCKWELL FUEL PUMP Filed March 17, 1930 s sheets-sheet 1 Dec. 5; 1'933. E A, ROC-KWELL 1,938,403

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Patented Dec. 5,' 1933 UNITED STATES Parrain*- OFFICE' 12 Claims.

Yfrom a source of supply to a place of use, such as may be associated with internal-combustion engines, for delivering fuel from the supply tank to the carbureter of the engine.

Fuel pumps as heretofore constructed have comprised a pump body adapted to be mounted on the engine casing andincluding a variable capacity pumping chamber by means ofwhich the fuel is drawn from the source of supply and delivered from the pump through the movement of a diaphragm pumping member actuated from the movement of a cam on a shaft within th engine casing.

It is customary to associate' with the pump body, a. removable sediment trapping `and filter chamber into which the fuel is delivered prior to its flow into the pumping chamber. further usual to mount inlet and outlet springpressed check valves in the pump body which prevent return ow of the fuel. In order to develop the high suction required for drawing the fuel through the supply tubing from the supply tank, the intake stroke of the pumping member should be substantially positive in its action. The fuel pump must be designed to deliver the maximum amount of fuel which may be consumed by the engine but at periods of low consumption by the engine, it is necessary that somemeans be employed for cutting down further delivery of fuel, for example, if the fuel pump delivers to a oat chamber, the closing of the oat control valve develops a back pressure on the pump which serves to limit the delivery of fuel by the pump.

- the pumping member is given a constant stroke for both intake and discharge, a. regulation may be obtained by either re-circulating the fuel in Y some manner or by providing means bywhich the movement of the pumping member in al direction to reduce the capacity of the pumping chamber causes the movement of a control member which prevents reduction in. the capacity of the pumping chamber. Thus the pumping chamber may include in its walls, a. pair of It isdiaphragms, one of which is given a constant stroke at all times and the other of which is resiliently urged ina direction to reduce the capacity of the pumping chamber and does not move until the maximum pressure permitted is 00 reached, whereupon the second diaphragm moves in accordance with the movement of the pumping diaphragm in such a manner as to prevent a change in the capacity of the pumping y chamber and stop further delivery through the outlet check valve. I

It is a purpose of the present invention to provide improvements in fuel pump construction in which a pumping diaphragm cooperating with the pumping chamber is given a. constant stroke from the action of the engine cam and the control of pressure developed by the pump is obtained by means of a second springpressed diaphragm arranged in such a manner as to maintain high eiiiciency of the pumpingmeans and to render the pump self-priming in its action by cutting down vthe clearance volum in the pumping chamber.

'It is an object of the invention to provide an auxiliary chamber in communication with the pumping chamber and to so mount the control diaphragm as a wall of the auxiliary in such manner that it normally serves `to close the communication between the pumping and auxiliary chambers. By this construction, the high suction pressure developed by the intake stroke of the pumping diaphragm tends to hold the control diaphragm tightly on its seat and does not subject the flexible portion of the control diaphragm -to' the suction pressure thereby 90 removing the duty from the control diaphragm and rendering the pimp more positive in its operation. This type of operation is more preferable than a former construction in which the intake stroke of the pinnping diaphragm subjects the full suction pressure to the control diaphragm.

It is further an object of the invention to so mount the control diaphragm that the delivery pressure of the pump initially acts against a small area of the control diaphragm but upon movement of the control diaphragm the delivery pressure is distributed over the entire areaof the lcontrol diaphragm. Thus the delivery pressure is immediately lowered as soon as the control diaphragm moves andthe maximum. pressure permitted cannot be exceeded. The improved results may be obtained by mounting a control diaphragm in such manner that its rigid central portion normally serves to close the communiw cation from the pumping chamber but upon movement of the control diaphragm to open the communication, the fuel pressure is distributed over the entire area of the diaphragm.

A further important feature of the present invention consists in the provision of a pump having an outlet air dome and vapor trap arranged just beyond the outlet valve in such a manner that the vapors which accumulate in the outlet trap serve to maintain a more uniform delivery of fuel from the pump by absorbing the intermittent impulses of the action of the pump and in which construction the accumulation of vapors for collection in the outlet vapor dome is increased by the action yof the control diaphragm. Thus, according to the present invention, the control diaphragm forms a wall of a restricted chamber and, after being moved in a mannerv to permit flow of the fuel from the pumping chamber to the auxiliary chamber, the control diaphragm is returned to its seated position by the suction stroke of the pumping diaphragm in such a manner that the fuel is substantially driven out of the auxiliary pumping chamber by a spanking action of the control diaphragm, thus producing vapors.

Further, according to the present improvements, it is an object of the invention that the control diaphragm cooperates with the pumping stroke, the auxiliary diaphragm which has been moved by the action of the pumping diaphragm is resiliently returned and serves to deliver a portion of the fuel through the outlet passage. This action renders the delivery of fuel from the pump more uniform and acts in some respects, similar to a double-acting pump.

Further and additional objects and advantages of the present improvements will be more readily apparent from the complete description taken in connection with the attached drawings in which preferred embodiments of the construction are illustrated.

In the drawings:

Figure 1 is a plan view of the pump body illus trating the angular disposition of the actuating lever with respect to the offset intake trap chamber.

Figure 2 is a vertical section taken on the line indicated 2-2 in Figure 1 in a manner to most clearly illustrate the internal portion of the pump.

Figure 3 is a detail section taken on the plane indicated by 3-3 in Figure 1 and illustrating the disposition of the intake and exhaust valves.

Figure 4 is a detail section taken on the plane indicated by 4-4 in Figure 1 and illustratingthe outlet passage from the pump.

Figure 5 is a plan view of a modified construction of the pump, and

Figure 6 is a vertical section taken on th plane indicated by 6-6 in Figure 5.

The embodiments illustrated in Figures 1 to gether and serve to retain a plunping diaphragm 12 in the usual manner. The diaphragm 12 cooperates with recessed portions of the casing parts to form a pump chamber 13, on the upper side of the diaphragm and a lower chamber 14 formed in the lower casing part 11. The lower casing part 11 includes an upwardly projecting boss 15, forming a guide bearing for a stem 16 attached to the pump diaphragm by a threaded nut 1'7 which serves to clamp to the opposite sides of the diaphragm a pair of disks 18 and 19. The construction of the disk supporting means for the diaphragm is similar to that described and claimed in my co-pending application, Serial No. 356,330, filed April 19, 1929, and for the purpose of the present invention, it is only necessary to understand that thedisk elements serve to prevent slack in the exible portion of the diaphragm. The diaphragm 12 is upwardly urged in such manner as to reduce the capacity of the pumping chamber and deliver fuel therefrom by the force of a resilient compression spring 20 surrounding the boss 15 and reacting between the bottom of the' chamber 14 and the lower disk 19 attached to the diaphragm.

The lower portion of the casing part l1 includes a chamber 21 into which the stem 16 extends and which is adapted to come into sealing relation with an engine casing 22 through an opening 23 cooperating with a lateral opening of the chamber 21. The casing .part 11 has a vertically disposed flange 24 which is attached tp the engine casing 22 in a suitable and customary manner. A fulcrum pin 25 is mounted in the casing part 11 in the chamber 21 and serves as a mounting for a double arm lever 26-27. The arm 26 of the lever has a yoke end 28 formed to slidably engage a cylindrical reduced portion 29 of the stem 16 in such a manner as to transmit positive movement to the stem 16 by the oscillation of the lever arm 26 about the fulcrum pin 25 and to permit a small amount of relative movement between the lever 26 and the stem 16, since the yoke end is moved in an arc while the stem 16 is moved in a straight line.

'I'he oppositely extending arm 27 of the lever includes a thrust portion 30 maintained in contact with an eccentric cam 31 mounted on an engine shaft 32 within the engine casing by the action of the compression spring 20. It will, therefore, be understood that the active movement of the cam transmits a positive movement to the pumping diaphragm to pull it down in a suction direction and compressing the spring 20. During the passive phase of the cam, the lever and the pumping diaphragm are substantially positively returned by the action of the stiff yspring 20. 'Ihe upper casing part l0 includes an integral lateral extension 33 to the lower portion of which is removably attached a glass cup 34 held by the securing means 35 and forming a sediment collecting and trapping chamber 36 into which the fuel is delivered through a centrally disposed passage 37 formed in the extension 33 and in communication with a horizontal passage38 having a threaded end 39 to which the suction pipe connection may be attached. The upper end of the glass cup 34 is brought into sealing engagement with a gasket 40 and further serves to retain a screen member 41 having a central opening seated around a depending shoulder 42 of the extension 33.

As illustrated by the detail section in Figure 3 both inlet and exhaust valves are carried in side-by-side relation by thecasing extension 33. Thus a chamber 43 is provided in the extension 33 in communication with the pumping chamber 13 by a lateral horizontal passage 44 and closed at the top portion by a removable threaded plug 45. A valve seat member 46 may be inserted through the top opening of the chamber 43 and extended through an opening in the bottom oi the chamber 43 to form a communication with the upper portion of the sediment collecting chamber 36 above the screen 41. An inlet check valve 47 is normally held in closed position preventing return flow into the chamber 36 by the action of a spring 48 surrounding a pin 49 carried by the plug 45.

The casing extension 33 includes an upward tubular extension 50 having in its lower portion a chamber 51 in communication with a passage 52, as shown in Figure 4, which is closed at one end by the plug 53. A collar 54 is placed into the tubular extension 50 from the open upper end and carries a valve seat member 55 which forms a communication between the lower chamber 5l and an upper chamber 56. The delivery of fuel from the chamber 56 is through a lateral passage and threaded connection 57 adapted to be connected to the delivery pipe which leads to the carbureter. A perforated transverse plate 5S is tted into the tubular extension 50 and serves to support a depending pin 59 against a shoulder of which a spring 60 is seated for bearing against the outlet check valve 61. The top of the tubular extension 50 is closed by a plug 82 having a hollowed out portion 63 forming an air or vapor dome in communication with the chamber 56 through the perfcrations in the transverse plate 58. The operation and construction of the vapor dome is described more in detail in my copending application, Serial No. 356,330, filed April 19, 1929, and it may be understood that the plate 58 efficiently operates to comb out the vapor and prevent filling up of the vapor dome by the accumulation of liquid fuel therein.

According to the usual operation, the fuel is drawn by suction from the source of supply and deliveredto the sediment collecting and nlter chamber from which it is passed through the intake check `valve by the suction stroke of the pumping diaphragm and is expelled from the pumping chamber through the outlet check valve by the discharge stroke of the pumping diaphragm.

As previously mentioned, it has been vcustomary to resiliently limit an effective discharge stroke of the pumping diaphragm by providing some means whereby the actuating lever may be given` a constant stroke while the pumping diaphragm may take a variable discharge stroke. According to the present construction the pumping diaphragm has a constant stroke in both directions and, therefore, some means must be employed independent of the action of the pumping diaphragm for limiting the pressure developed on the outlet of the pump and controlling the delivery of fuel therefrom.

The upper casing part l0 includes a central opening 64 which receives the threaded nut 17 during the movement of the pumping diaphragm and forms a communication with an auxiliary chamber 65 'included within a recessed portion of the casing part 10 and in communication with the outlet passage 52. A flexible diaphragm 66 seals the top portion of the auxiliary chamber 65v by having its annular edge 67 clamped to the casing part 10 by a cover member 68. The cover member 68 has a depending flange 69 fitting over to thecircular portion of the casing part 10 and is secured by the screw bolts 70, some of which may also serve as means for securing the upper and lower casing parts 10 and 11. The diaphragm 66 is strengthened by a pair of upper and lower disk members 71 and '72 in a manner similar to the pumping diaphragm l2. The disk members are attached to the diaphragm 66 by means of the nut'and bolt connection 73 and a coiled compression spring 74 is provided enclosed,

by the cover member 68 and positioned by a depending annular portion 75 and bearing against the upper disk member 7l whereby the diaphragm 66 is normally held in a position to reduce the capacity of the auxiliary chamber 65 and is held in stopped position by having the lower disk member '72 seat against a gasket 76 fitting into a recess in the casing part 10 surrounding the central 'passage 64. The spring 74 is of such strength as to limit the effective discharge pressure which may be developed by the action of the pump.

Vents 77 should be provided in the cover member 68 in order to maintain atmospheric pressure in the chamber above the regulating dia.- phragrn. Similarly a vent '78 is shown in the casing part 11 at the lower part of the chamber 14 beneath the pumping diaphragm in order that the lower side of the pumping diaphragm will be always subjected to atmospheric pressure.

In order to be sure that the construction of the pump illustrated in Figures 1 to 4 will properly prime at low speeds of the engine, it may be desirable to embody a construction such as illustrated in Figure 2 in which the boltof the nut and bolt connection '73 has a lower extension 80 over which is tted a cup-shaped leather washer 81. A washer 82 is held between the head of the bolt andthe lower disk '72 and includes spring tongues which are adapted to be bent over the flange of the Washer 82 to retain the same in place. The extension from the control diaphragm is provided in order that the pumping diaphragm, when at the limit of its upward stroke, will positively unseat the control diaphragm by contacting the leather washer 82 by means of the threaded vupward extension from the diaphragm stem 16. By this construction the clearance volume in the `pumping chamber is cut down by the seating of the control diaphragm during the suction stroke of the pumping diaphragm. During the priming of the pump, the discharge stroke of the pumping die.- phragm will produce a compression of the air in the pumping chamber, which might not be sufficient to lift the control diaphragm, but the final portion of the discharge stroke by positive unseating of the control diaphragm, will permit the exhau't of the trapped air. After the pump has been primed the operation of the pumping diaphragm will not produce -a direct contact with the leather washer which covers the depending extension from the control diaphragm since the control diaphragm will be opened by the pressure produced on the fuel in the pumping chamber.

The operation of the pump will be now described. Movement of the pumping diaphragm 12 in a downward direction so as to enlarge the capacity of the pumpingchamber 13 will serve to draw the upper control diaphragm 66 more tightly against its seat on the gasket 76 by acting against the rigid central portion of the upperA diaphragm. The entire suction force developed will therefore be expended in drawing fuel from the source of supply into the intake trap chamber 36 and past the inlet check valve into the pumping chamber 13. There is, therefore, no tendency for the flexible portion of the upper diaphragm 66 to yield on the suction. stroke of the pumping diaphragm 12 and, therefore, the heavy duty of the suction pumpingaction is removed from the secondary diaphragm. Movement of the lower diaphragm 12 in an upward direction through the force of the spring 20 will serve to reduce the capacity of the pumping chamber 13 and since the return flow through the diaphragm 66 will be more readily moved in an upward direction. The fuel will therefore be delivered upward through the chamber 65 and outward in the direction of the outlet check valve through the delivery pipe line of the pressure chamber at a rate determined by the resist ance of the spring 74. The pressure on the out- A let, if not sufiicient to fully counteract the inertia of the fuel in the delivery pipe line, will be absorbedby the compression of the vapor in the outlet dome 65 which will tend to cause a further iiow during the next suction stroke of the pump.

It will be further apparent that the upper diaphragm 66 will take a variable stroke in an upward direction dependent upon the volume of fuel which may be delivered through the outlet connections. Upon the return stroke of the pumping diaphragm in a suction direction the diaphragm 66 will be returned by the force of the spring 74 and by the suction in the pumping chamber 13. During the return stroke of the diaphragm 66 some fuel will be delivered through the outlet passage from the auxiliary chamber 65 since the restriction to the ow of the fuel back into the pumping chamber 13 is greater than the restriction to theflow through the outlet passage 52. This construction is more desirable than a form in which the control diaphragm is inactively returned without performing any pumping in which construction a suction pressure is not developed until the control diaphragm is brought to its stop position. The discharge stroke of the pumping diaphragm 12 produced by the force of the spring 20 causes a movement of the control diaphragm 66 and compression of the spring 74, and the work expended in compressing the spring 74 is utilized upon the return stroke of the control diaphragm 66 by the performance of a pumping action. The operation of the pump in some respects is similar to that of a double acting pump and a much higher efficiency will be obtained than in previous constructions of single action fuel Dumps.

A vslightly modified construction is illustrated YVinwlligures 5 andv 6, the principal difference being that the outlet passage from the pumping the pumping chamber andthe auxiliary chamber does not come into use except when the control diaphragm is moved bythe pressure in thev vpumping chamber exceeding the resilient pressure of the spring which controls the upper diaphragm. Similar reference numerals have been applied as far as possible to the construction of Figures 5 and 6 as previously applied to the construction shown in Figures 1 and 4, and it will onlybe necessary to refer to the modified construction in describing this form of pump.

The passage 44 from the inlet check valve 47 to the pumping chamber is extended beyond `the valve chamber to a passage 441 closed at the end vby a plug 531 and in communication with an upward extension 501 of the casing part 10. 'Ihe extension 501 includes the outlet check valve and the vapor dome similar to the construction in Figure 3, thus a plug 541 fits into the lower portion of the extension 501 forming a seat for a valve seat member 551 having a passage therethrough controlled by a check valve 611 and communicating with a chamber 561 from which the fuel is delivered through a threaded connection 571 to the outlet pipe line. At the upper portion of the extension 501 a perforated transverse plate 581 is seated in a shouldered portion of the extensio'n 501 and retained in place by a threaded plug 621 which forms a vapor trap chamber 631 above the perforated plate 581. The perforated plate forms a support for a stem 591 retaining at its lower end a spring 601 which bears against the outlet check valve 611. According to this construction the fuel is impulsed in-opposite directions through the passage 44 by the expansion and contraction of the pumping chamber 13. The contraction of the pumping chamber 13' will serve to deliver the fuel through the passages 44 :and 441 past the outlet check valve 611 and out; of the pump through the threaded connection 571. The vapors are combed out of the fuel and collected in the chamber 631 by passing through the perforated plate 581.

It will be apparent that the pressure of the fuel being pumped is not applied to the flexible portion of the upper diaphragm 66 as long as the rigid central portion of the diaphragm 66 is maintained against its seat on the gasket v76.

it has initially moved away from the seat. As

long as the delivery of fuel past the outlet check valve is prevented, the upper diaphragm 66 will move in such a manner as to follow the movement of the pumping diaphragm 12 and to maintain a constant capacity within the pump A' f' until the pressure falls suiciently to again permit delivery. The upper diaphragm 66 will again come to seating position and, due to the foil restricted proportions of the auxiliary chamber, v

the seating of the diaphragm 66 will tend to produce vapors which later collect in the outlet `vapor dome and serve to prevent the liquid fuel from filling the dome and em'ciently maintain ydelivery at a uniform pressure.

The pump construction as described in Figures 5 and 6 does not require the provision of means for positively moving the control diaphragm during priming since, in this case, the air which istrapped in the pumping chamber is expelled through the outlet check valve during the priming strokes of the pump and the control diaphragm will remain in seated position until moved by the pressure of the fuel.

claim:

l. A fuel pump comprising a casing, inlet and outlet connections thereto, check valves mounted in said casing, expansible and reducible primary and secondary chambers within said casing, a :dow passage between said chambers, an independent inlet passage from said inlet check valve to said primary chamber, an independent outlet passage from said secondary chamber to said outlet check valve, means for uniformly enlarging and reducing the capacity of said primary chamber and resilient means controlling the expansion and reduction of said secondary chamber for variably controlling the delivery of fuel through the outlet passage and outlet check valve.

2. In a construction of fuel pump as described in claim 1,-a flexible wall movable by said resilient means and an annular seat surrounding the ow passage between said chambers for limiting the inward movement of said wall.

3. In a construction of fuel pump as decribed in claim 1, a primary pumping diaphragm forming a wall of said pumping chamber, a secondary control diaphragm forming a wall of said secondary chamber, said secondary diaphragm being movable by said resilient means in a direction to restrict the flow of fuel through the passage between said chambers.

4. In a construction of fuel pump as described in claim l, a exible diaphragm forming a wall of said secondary chamber'having a rigid central portion, said rigid central portion being movable by said resilient means to substantially close the passage between said chambers whereby the expansion of the pumping chamber subjects the rigid central portion of said diaphragm alone to the force of the suction pressure.

5. A'fuel pump adapted to variably deliver fuel to an internal combustion engine comprising an expansible and reducible' pumping chamber, a movable pumping member forming a wall of said chamber, an auxiliary chamber in communication with said pumping chamber, a resiliently movable member forming a wall of said auxiliary chamber, an outlet passage from said auxiliary chamber independent of the communication between said chambers and a check valve in said outlet passage seating against the direction of fuel ow and independent of said resiliently movable member, whereby said check valve remains seated above a predetermined discharge pressure.

6. A fuel pump adapted to variably deliver fuel to an internal combustion engine, comprising a pump casing having valve controlled intake and exhaust passages, a pumping chamber in com-V munication with said intake passage, an auxiliary chamber in communication with .said exhaust passage, a pumping member having a substantially constant stroke forming a wall of said pumping chamber and a resiliently movable member forming a wall of said auxiliary chamber, saidvchambers being in communication independently yof the intake and exhaust passages.

7. A fuel pump adapted to variably deliver fuel inlet and outlet 4 to an internal combustion engine comprising a casing member having oppositely recessed faces, an inlet passage formed in said casing member extending into the recessed portion of one face, an outlet passage extending into the recessed portion of the other face, a flow passage through said casing member between said oppositely recessed faces, a pumping diaphragm clamped to one face of said casing member forming a pumping chamber through which the fuel flows from the inlet passage through said casing member, a control diaphragm clamped to the opposite face of said casing member forming an auxiliary chamber, means for imparting a substantially constant stroke tothe pumping diaphragm and resilient means reacting against the exterior of said control diaphragm whereby the movement of the pumping diaphragm draws fuel into the pumping chamber from the inlet passage and delivers the fuel through the auxiliarychamber and through the outlet passage, the pressure at, which the fuel is delivered being limited by the resilient pressure on the control diaphragm.

8. A fuel pump adapted to variably deliver fuel to an internal combustion engine comprising a casing member, a pair of recessed portions on opposite faces of said casing member, a dow passage between said'l recessed portions, independent inlet and exhaust passages in communication with said recessed portions respectively, a pumping diaphragm covering the recessed portion on one side of said casing forming a pumping chamber, a control diaphragm secured to the opposite face of said casing member forming an auxiliary chamber, a second casing member 110 covering. the exterior of said pumping diaphragm, actuating means connected to said pumping diaphragm mounted inv said second casing member, a compression spring mounted in said second casing member in position to react 115 against said pumping diaphragm in a direction to reduce the capacity of said pumping chamber,

a removable cap for covering the exterior of said control diaphragm secured to said first mentioned casing member, a compression spring re- 120 acting between said cap and said control diaphragm in a direction tol reduce the capacity of said auxiliary chamber and meanscarried by v said first casing member to limit the inward movement of said control diaphragm by engag- 125 ing the inner face thereof.

9. A fuel pump adapted to variably deliver fuel to an internal combustion engine comprising an expansible and reducible pumping chamber, a movable pumping member forming a wall 130 of said pumping chamber, an auxiliary chamber in communication with said pumping chamber, a resiliently movable member forming a wall of said auxiliary chamber, an outlet passage from said auxiliary chamber independent of the communication between said chambers and means for positively moving the movable wall of the auxiliary chamber at the end of the discharge stroke of the movable pumping member should the pressure developed in the pumping chamber be insufficient to move the movable wall of the auxiliary chamber.

charge pressure in said pumping chamber comprising, an auxiliary chamber, a flow passage between said chambers, an outlet passage from said auxiliary chamber independent of the ilow passage between the chambers, a movable control member forming a wall of said auxiliary chamber, resilient means acting upon said control member to normally urge said control member into position closing said ilow passage and means for positively unseating the control member at the end of the discharge stroke of the pumping chamber should the pressure developed in the pumping chamber be insumcient to unseat the control member.

1l. A fuel pump adapted to variably deliver fuel to an internal combustion engine comprising an expansible and reducible pumping chamber, a movable pumping member forming a wall o! said pumping chamber, means for imparting a substantially constant stroke to said pumping member, an auxiliary chamber in communication with said pumping chamber, an outlet passage Irom said auxiliary chamber independent of the communication between said chambers, a control member forming a wall of said auxiliary chamber and comprising a rigid central portion and a ilexible annular portion, resilient means normally urging said rigid central portion into position to close the communication between said chambers whereby the exible annular portion of the control member is not subjected to the force of theV suction pressure produced by the movement of the pumping member in a direction to expand the pumping chamber and means for positively unseating the rigid central portion of said control member at the end of the discharge stroke of the pumping member in order to permit priming of the pump should the pressure developed in the pumping chamber be insuillcient to unseat the control member.

12. A fuel pump adapted to variably deliver fuel to an internal combustion engine comprising an expansible and reducible pumping chamber, an expansible and reducible auxiliary chamber, inlet and outlet passages and check valves controlling said passages for one-way iiow therethrough, said inlet .passage being in communication with said pumping chamber and said outlet passage being in communication with said auxiliary chamber, a pair of opposed exible diaphragms, each of said diaphragms being mounted to form a Wall of said chambers, a ilow passage between said chambers arranged on the axis of said diaphragms, a seat for one of said -diaphragms surrounding said flow passage, resilient means normally urging said last-mentioned diaphragm into contact with said seat',vmeans for imparting a substantially constant stroke to the other of said diaphragms and means carried by one of said diaphragms adapted to contact at the end of the discharge stroke of said constant stroke diaphragm in order to positively unseat the other of said diaphragms should the pressure developed in the pumping' chamber be insuiiicient to unseat the diaphragm.

EDWARD A. ROCKWELL.

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