US2096711A - Fuel pump for injectors - Google Patents

Description

Oct. 26, 1937. A. FIELDEN FUEL PUMP FOR INJECTQRS 2 Sheets-Sheet 1 Filed Nov. 28, 1934 Oct. 26, 1937. A. FIELDEN FUEL PUMP FOR INJECTORS Filed Nov. 28, 1934 2 sheets sheet 2 Patented Oct. 26, 1937 UNITED STATES FUEL PUMP FOR INJECTORS Arthur Fielden, Detroit, Mich., assignor to General Motors Corporation, Detroit, Mich, a corporation ,of Delaware Application November 28, 1934, Serial No. 755,157

25 Claims.

This invention relates to pumps and especially toplunger pumps 'for intermittent delivery of fluid through a pressure loaded delivery valve during the middle portion only of the discharge stroke of the plunger, the beginning and ending of each discharge stroke being made ineffective for delivery through the loaded delivery valve by the opening of suitable bypass or relief ports providing an alternative path for the flow of fluid from the pump pressure space during these portions of each discharge stroke.

It relates particularly to injection pumps for the supply of fuel to an internal combustion enr gine in which the pressure loaded delivery valve may constitute an injection valve.

Such an injection-pump in one unit with an injector, is shown in U. S. Patent No. 1,981,913,

wherein a part of the charge in the pump pressure space is rejected therefrom, through bypass 20 or relief ports controlled by the pump plunger, into a single annular chamber surrounding the plunger cylinder barrel and forming a reservoir, constituting a part'of the supply line to the pump, for fuel at low pressure from a suitable source. 25 Rejection of fuel into this supply line takes place before and after the delivery of a variable measured quantity of fuel at high pressure through the loaded delivery valve. An air cushion chamher. or any other suitable form of resilient storing 30 space suflicient to hold the volume of fuel rejected on any discharge stroke and to form a resilient cushion for the pressure surges in the supply line, is provided in communication with the uppermost part of the reservoir. The fuel rejected before delivery through the loaded delivery valve is rejected from the uppermost part of the pump pressure space, thereby eliminating along with the rejected fuel any air or gas bubbles which will rise to the uppermost part 'of the pressure space, before delivery takes place, the pump plunger moving downwardly on its delivery stroke for the injection of fuel downwardly into an engine cylinder. The pump plunger is 45 provided'with helical control edges whereby the time and quantity of fuel delivered may be varied'in known manner by a turning adjustment of the plunger.

The present invention relates to improvements 50 in the unit fuel pump and injector shown in Patent No. 1,981,913 and to a modification enabling the functional results of the structure shown in Patent No. 1,981,913 to be obtained in those cases where the assembly is inverted 55 for the injection of fuel upwardly into an engine cylinder, the plunger moving upwardly on its delivery stroke.. I V

One object of the invention is a fuel pump of the kind described in which the amount of fuel bypassed before delivery through the loaded de- 5 livery valve is constant, or alternatively, directly proportional to the amount delivered through the loaded delivery valve.

Another object of the invention is a fuel pump of the kind described having positive valve venting means open through a certain period of the cycle of operation of the pumpto relieve the reservoir of any excess air or gas bubbles.

' Another object of the invention is to provide for a through flow scavenging of the reservoir at the fuelsupply pressure.

A further object of the invention is to provide for air venting of the reservoir at a pressure higher than the fuel supply pressure.

A still further object of the invention is a modification of the structure of the unit fuel pump and injector of U. S. Patent No. 1,981,913 adapted for operation in a relatively inverted position for upward injection of fuel and having the foregoing objects of the invention applied thereto.

The above and other objects of the invention will be apparent as the description proceeds.

According-to the invention, that control edge on the pump plunger which controls the closure with the latter arrangement, the degree of preliminary bypassing may be proportional to the quantity delivered.

The venting of the reservoir both for the elimination of air from the system and for any desired amount of "through flow scavenging is effected tive valve means for venting the reservoir for the elimination of undesired air in the system enables this elimination to be positively effected with a minimum of through flow of fuel, thus reducing the quantity of fuel to be recirculated through the low pressure supply system and hence avoiding any infiltration of additional air in the fuel so recirculated.

The velocity of air or gas at a certain pressure through an orifice being several times greater than the velocity of a liquid at the same pressure through the same orifice, the bore of the vent and the time which it remains open can be made such that all undesired air or gas can be eliminated from the reservoir, while only a comparatively small amount of liquid fuel can escape through the vent in the same circumstances.

By suitably disposing on the pump plunger the control edge or edges for the vent port, the reservoir may be vented either before the beginning of the discharge stroke at the supply pump pressure, or after the end of the discharge stroke at a pressure higher than the supply pump pressure, in a manner later to be described.

The accompanying drawings show the application of the invention to a fuel pump of the kind described arranged for upward injection and alternatively for downward injection of fuel.

In the drawings:

Figure 1 shows in part sectional elevation, a

combined fuel pump and injection nozzle of the kind described, mounted in the cylinder head of an internal combustion engine and discharging upwardly thereinto.

Figure la is an enlarged view of a part of Figure 1 showing the injection nozzle.

Figure 2 is a perspective view of a suitabl check valve for the bypass port to prevent the influx of fuel'into the cylinder barrel through this port.

Figure 3 is a section on line 3--3 of Figure 1 showing the means for angular turning adjustment of the plunger, to vary the time and quantity delivered through the loadedv delivery valve.

Figure 4 is a section on line 4-4 of Figure 1.

Figure 5 is a section on line 55 of Figure 1, showing the means of locating the cylinder bushing in the pump housing and the ducts for draining excess air and fuel leakage away from the injector.

Figure 6 is an enlarged perspective view of the end of the pump plunger showing a control edge for the closure of the inlet port providing for a constant interval between closure of the inletport and closure of the preliminary bypass port as shown in Figures 7, 9 and 10.

Figure 7 shows a fuel pump similar to Figure 1, but having a plunger controlled port 'for the air venting and pressure relief of the reservoir, and a combined check valve and safety valve in the supply line.

Figure 8 is-an enlarged section on line 8-8 of Fig. '7.

Figure 9 shows a fuel pump for use with injectors discharging downwardly, having "a plunger controlled port for the air venting and pressure relief of the-reservoir, and a combined check" valve and safety valve in the supply line.

Figure 10 shows a modification of Figure 9 with .means for opening the port for the air venting and pressure relief of the reservoir at the end of the discharge stroke of the pump plunger.

Figure 11 shows a similar modification of Figure 7.

Figure 12 is an enlarged view of a part of Figbushirig in the housing I.

" pocket 20 for a spring 2|.

edge I. An annular groove or space 2 divides the circumferential surface of the plunger into two parts. The annular groove isbounded by a helical edge 3 and a helical edge 4.

The plunger works in a cylinder 8 which is a Between the bushing and the housing is an annular chamber 8 formed by an enlarged bore of the housing. Two ports 9 and Illthrough the wall of the bushing 6 connect the annular chamber 8 with the bore of the bushing.

A duct drilled through the housing into the end of the annular chamber 8 serves for the supply of fuel to this annular chamber from any suitable low pressure source.

The housing is counterbored to form a pocket l3 for a pinion |4 having a bearing formed by a boss I5 extending into the bore of the housing and having a clearance between itself and the end of the bushing to provide a space Hi therebetween.

The plungerl has a' hexagonal spline portion l! in the pinion I4 so that it may be turned thereby, but is capable of longitudinal reciprocating motion therein. The pinion l4 may be angularly turned for adjustment of the beginning and end of injection by a rack I8 which can slide back and forth in a horizontal groove IS in the housing, opening out into the pocket IS. The rack is retained in the groove by a plate l9.

The housing I is counterbored to provide a The outer end of the plunger is provided with a head 22 and a seating collar 23 for the spring 2|. The other end of the spring is provided with a seating collar 24 bearing against the end of the pocket 26.

The outer end of the plunger with its spring is enclosed by a cover 25, which reciprocates in the pocket 20 under the influence of any suitable driving means. As shown,the plunger is actuated on its discharge stroke, through the medium of a rocking lever 26 with rollers 26 and 26", by a cam 21, the spring 2| effecting the return or suction stroke of the plunger.

The end of the housing 1 is internally threaded for the injection valve parts, consisting of a nozzle piece 28, a valve seat piece 29, and,a distance piece 30 constituting a spring .housing, .all within a bored out threaded cap piece 3|, which screws into the housing. 7

The nozzle piece 28 has a conical seating in the cap piece 3|, and all three parts 28, 29 and 38, together with the bushing-6, are clamped tightly together and onto a shoulder 32 in the housing I, when the cap piece 3| is screwed therein, leaving a clearance space 33 between the bushing and the cap piece 3|.

A duct or ducts 34 through the piece 30 lead the fuel from the pump pressure space to a duct or ducts 36, leading to a chamber 31 in the piece 29. In this chamber 31 is a seating for an 111-- collar 44 on a stem piece 45 for the valve which I predetermined amount.

The strength of the spring 43 and the loading it provides for the injection valve 38 which is the loaded delivery valve of the pump determines the minimum injection pressure.

The port It! is provided with a check valve of any suitable type. In the example illustrated, it consists of a fiat spring 48 curved to fit tightly in a shallow annular groove 49 around the bushing 6, with one end over the port I and the other end locating and holding the spring in position by a projection or dimple 50 formed thereon, and sprung into a corresponding depression in the bushing.

The bushing 6 is located in the housing I with its ports 9 and I0 at'a normal definite angular relationship to the housing by a pin 52 (see Figure 5).

A small screw 53 through the housing 1 engages a slot 54 in the cover 25, retaining the cover over the plunger and its spring, but permitting its reciprocating movement.

The complete assembly constitutes a unit fuel pump and injection nozzle which may be mounted in a suitable bore through the cylinder head of an internal combustion engine.

As shown, the cap piece 3| of the combined fuel pump and injection nozzle has a conical seating in a bore through a'cylinder head 55 in which it is held by-the studs 56. A-suitable clearance between this bore and the housing! provides an annular space 51 into which all leakage and ventage from the pump may collect.

The clearance space I5 is connected to the annular space 51 by a port46' inFigures 1, 5, '7 and 11 and by a port 46 in Figures 9 and 10.

Leakage and excess fuel is returned from the? annular space 51 to a supply tank (not shown) through a duct 58' in the injector housing in Figures 1, '5, 7 and 11, and with the construction according to Figures 9 and through a duct 58 in tween the pressure space and the annular groove.

The flanged end 60 of the cylinder barrel 6 which is clamped onto the shoulder 32 of the housing 1 has its periphery grooved by channels 6| which connect the reservoir 8 with the clearance space 33 which constitutes an air cushion chamber.

In Figure 1 a leakage path for air in excess of that required to fill the chamber 33 is provided by a fitting of the parts such that there is a slight clearance between the periphery of the flange 68 and the housing. I, and air which leaks therebetween'from the cushion chamber 33 passes to the outside of the housing through a drain hole 62. 1 v

The operation of the construction for upward injection of the fuel according to Figure 1, is as follows: fuel at a small head of pressure is supplied to the annular chamber 8 through the duct II. In the position shown, the plunger lis at the end of its suction stroke and has uncovered the inlet port 9, allowing oil to fiow into the pumping space. As the plunger is'moved inwards on its discharge stroke, it first covers the inlet port 9 and then pumps oil and any gas bubbles the fuel in the reservoir.

mixed therewith out from the uppermost part of the pumping space 5' through the duct 5' into the annular space 2 and out through the bypass port l0 back into the annular chamber 8 until the edge 4 covers the port l0. At this point, and there now being no other outlet from the pumping space, the pressure rises rapidly in the pumping space and its connections with the chamber 31 containing the spring loaded valve 33, until voir 8. The air chamber 33 acts as a. pressure accumulator, reducing the pressure variations on the inlet side of the pump as a result of the opening and closing of the ports 9 and Il Excess air in the airchamber 33 escapes at any time through the port 62, by virtue of the clearances provided.

It will be noted that in the construction according to Figure 1, the edge I of the plunger, which controls the closure of the inlet port 9 is cut square with its axis, and therefore if thetime of closing of the bypass port ID by the helical edge 4 is advanced by a turning adjustment of the plunger, the quantity bypassed before the beginning of injection will be lessened'while the quantity injected is increased, and vice versa.

In order to ensure the elimination of air and gas bubbles from the pump pressure space along with the volume bypassed before the beginning of injection 'it is desirable that this bypassed volume should be at least constant or directly proportional to the amdunt of fuel delivered through the injector and not lessened when the quantity injected is increased.

Referring now to Figure 6, it will be noted that the edge I of the plurfger--which is the control edge for the closure of the inlet port 9- -is helical and of the same pitch as the helical edge 4 which controls the closure of the bypass port l8; 1. e. it has the same lead or advance as the helical edge 4, and therefore if in the plunger stroke the time of closing of the bypass port is advanced or retarded by a turning adjustment of the plunger, the time of closing of the inlet port will be advanced or retarded to a like extent, and the distance moved through by the'pump plunger between closure of the inlet port and closure of the bypass port will be constant; hence the volume bypassed through the bypass port I0 before the beginning of in? ction will be invariable.

If the pitch of the helical edge .I is increased to the proper degree greater than the pitch of the helical edge 4, the inlet port 9 will be closed earlier as the bypass port I8 is closed earlier, and

- the volume bypassed through the bypass port M before the beginning of injectionmay be made directly proportional to the amount of fuel delivered through the injector.

I In Figures '7 and 11, air or vapor separating out from the fuel in excess of that requiredto fill the cushion chamber 33 is displaced from the reservoir 8 through a duct 61 by the pressure of In Figure '7 this venting of the reservoir takes place along with a through flow of the fuel, during the dwelP' period provided by a dwell portion on the cam 21, between suction and discharge strokes of the pump, there being an annular groove 68 around the plunger which during this period puts the duct 61 in communication with a port 68 in the bushing, leading to the annular space 51 through a coincidental port 10 in the housing. In Figure 11, the venting of the reservoir takes place at the end of the dischargestroke of the pump plunger, the plunger having a portion of reduced diameter bounded by an edge 12, which, at the end of the discharge stroke, puts the vent duct 61 in communication with the clearance space i6 which is connected with the annular space 51 and the drain duct 58' by the port 46'.

The operation of the constructions for downward injection of the fuel accord ng to Figures 9 and 10, is, in its essentials, functionally identical with that of the constructions according to Figures 7 and 11, respectively. In Figures 9 and 10 the pressure space in front of the plunger and the annular groove 2 are in= communication with each other at all times through the groove 5 in the plunger. On the closing of the inlet port, oil and any gas bubbles mixed therewith are pumped out through the bypass port i8 directly from the annular space 2. A bore l2 extending upwards from the upper end of the annular reservoir chamber 8 and having its outer end closed by a screwed plug !2' constitutes the'air cushion chamber. The end of the bushing 5 away from the injection valve is a. tight fit in the housing 1. Airor vapor separating out from the fuel in excess of that required to fill the cushion chamber I2 is displaced from the reservoir 8 through a port 63 by thexpre'ssure of the fuel therein. In Figure 9-this venting of the reservoir takes place along with a through flow" of the fuel during the dwell period between suction and discharge strokes of the pump, there being an annular groove 64 around the plunger which, during this period, puts the port 68 in communication with a drilled hole 65 in the bushing 6, leading to the clearance space l6 and thence throughthe port 46 into the annular space 51. In Figure 10 the venting of the reservoir occurs at the end of the discharge stroke of the pump plunger, the plunger having a portion of reduced diameter bounded by an edge 13 which, as the plunger approaches the end of its discharge stroke, puts the vent port 63 in communication with the clearance space l6 which communicates through a port 46 with the annular space 51.

The arrangements according to Figures '7, 9,

10 and 11 having valved venting of the reservoir, 8 are preferably provided with a combined nonlar passage through which, when the member 14 is oil its seating, fluid may flow through radial grooves such as in the end of the pipeunion, into the supply pipe 18-.

Within the valve member valve 8| yieldingiy urged onto its seating 82 therein at that end thereof remote from the seating 1rby-aspringr83l lhesprings 83 and 11 are respectively such that fluid can flow through the ball check valve 8| into the duct I i and reservoir 8 u is a ball check from the supply pipe 18 whenever the pressure therein is less than the supply pressure, and can flow through the safety valve 14 out from the reservoir 8 and duct II when the pressure therein is greater than the supply pressure to an extent governed by the pressure of spring 11.

With such a non-return and safety valve in the supply line, the pressure in the annular reservoir 8 will rise during the period of preliminary bypassing and again upon the opening of port 8 to terminate injection to a pressure higher than the supply pressure, but not greater than a maximum, controlled by the spring loading of safety valve 14 which is, of course, arranged to open at so ne suitable pressure lower than the pressure required to lift the injection valve or: its seat. In this way an intermediate pressure stage between supply pressure and injection pressure will be built up in the'reservoir 8 in every cycle of the pump plunger.

In the constructions according to Figures 7 and 9, this intermediate pressure, higher than the supply pressure, will be effective to recharge the pumping space on the suction stroke until the pressure in the reservoir 8 falls to supply pressure, when the non-return ball check valve 8| will open the reservoir to the source of supply. A more rapid filling of the pump pressure space is thus obtained, which is advantageous in a pump working at high speed.

In the modifications according to Figures 10 and 11, the intermediate pressure will be relieved by the opening of the vent port 68 and the vent stroke, whereby the reservoir is vented at a pressure higher than the supply pressure.

In all the arrangements according to Figures 7,9, 10 and 11 and provided with a non-return and safety valve as described in addition to the foregoing and to the fact that high pressure surges will not normally be transmitted to the supply line, the intermediate pressure stage built up in the reservoir on each discharge stroke will be eflective to reduce leakage between the plunger and the cylinder barrel by reducing the pressure difference on the inside and outside of the cylinder barrel and thus reducing the stresses safety valve- -less than the pressure required to hold theinjection valve ofl." its seat.. While,

however, the reservoir has been shown with such an air chamber space to constitute a resilient capacity expansible under pressure, the invention is not limited to such a specific means of ab- 1. A fluid pump comprising a cylinder, 9.

plunger in the cylinder, the said plunger moving upwardly on its discharge stroke and delivering fluid upwardly through an upwardly directed delivery outlet, an inlet port and 'a bypass port in the cylinder, the bypass port being lowermost and axially spaced from the inlet port, the delivery outlet being above the inlet port but below the uppermost part of the pump pressure space, control edges for the ports constituted by the end of the plunger and the two edges of an annular groove therein, a duct connecting the uppermost part of the pump cylinder pressure space with the annular groove in all positions of the plunger in which either the inlet port or the bypass port is open to the annular-groove, and forming the only connection between the pump pressure space and the annular groove, all whereby, on the discharge stroke of the pump, the bypass port is open after the inlet port has closed and a part of the pump charge including any air or gas bubbles is expelled through the bypass port from the uppermost part of the pump cylinder pressure space after the closure of the' inlet port and before discharge through the delivery outlet consequent upon closure of the bypass port.

. 2. In a fluid pump having a cylinder, a plunger cooperative therewith as a pump for the pressure discharge of a predetermined quantity of fluid through a delivery outlet, coacting ports and control edges therefor on the cylinder and plunger, respectively, including an inlet port and a bypass port whereby fluid is bypassed out from the cylinder after the closing of the inlet port and before the pressure discharge through the delivery outlet, the control edges for closing the inlet and bypass ports being inclined and so arranged that Y upon a relative adjustment of the cylinder and plunger the inlet port is closed earlier as the bypass port is closed earlier, the inclination of the control edge for closing the inlet port being not less than the inclination of the control edge for closing the bypass port, whereby the quantity bypassed before discharge through the delivery outlet is not lessened as the bypass port is closed earlier. 7

. 3. In a fluid pump having a cylinder, a plunger cooperative therewith as a pump for the pressure discharge of a predetermined quantity of fluid through a delivery outlet, coacting ports and conrespectively, including an inlet port and a bypass port whereby fluid is bypassed out from the cylinder after the closing of the inlet port and before the pressure'discharge through .the dethe quantity bypassed before discharge throughthe delivery outlet remains constant irrespective of the time of closing of the bypass port.

4. In a fluid pump having a cylinder, a plunger cooperative therewith as a pump for the pressure discharge of a predetermined quantity of fluid through a delivery outlet, coacting ports and control edges therefor on the cylinder and plunger, respectively, including an inlet port and a bypass port whereby fluid is bypassed out from the the inclination of the control edge for closing the bypass port, whereby the quantity bypassed before discharge through the delivery outlet is increased as the bypass port is closed earlier.

5. In a fluid pump having a cylinder, at plunger cooperative therewith as a pump: for the pressure discharge of a predetermined quantity of fluid through a delivery outlet, coacting ports and control edges therefor on the cylinder and plunger respectively including an inlet port and a bypass port whereby fluid is bypassed out from the cylinder after the closing of the inlet port and before the pressure discharge through the delivery outlet, the control edge for closing the bypass port being inclined so that the time of closing of the bypass port is variable by a relative adjustment of the cylinder and"plunger, the quantity delivered being increased as the bypass port is closed earlier, the control edge for closing the inlet port being inclined and so arranged that the inlet port is closed earlier as the bypass port isclosed earlier, said lastnamed control edge having an inclination not less than the inclination of the controledge for closing the bypass port whereby the quantity bypassed before discharge through the delivery outlet is not lessened as the quantity delivered is increased. t

6. The combination according to claim 5 in which the control edge for closing the inlet port has an inclination equal to that of the control edge for closing the bypass port, whereby the quantity bypassed before discharge through the trol edges therefor on the cylinder and plunger,

cylinder after the'closing of the inlet port and before the pressure discharge through the delivery outlet, the control edges for closing the inlet and bypass ports being inclined and so arranged that upon a relative adjustment of the cylinder and plunger the inlet port is closed earlier as thebypass port is closed earlier, the inclination of the control edge for closing the inlet port being greater than I delivery outlet-remains constant as the quantity delivered is increased.

'1. The combination according to claim 5 mwhich the control edge for closing the inlet port has an inclination greater than that of the control edge for closing the bypass port, whereby the quantity bypassed before discharge through the delivery outlet is increased as the quantity delivered is increased. g

8.- In a fluid pump comprising a cylinder and a plunger cooperative therewith as a pump, a delivery outlet for the pressure discharge of a part only of the volume of fluid displaced by the pump, a. reservoir for fluid under pressure forming part of the supply line to the pump from a low'pressure source of supply, inlet and bypass valve means between the pump pressure space and the reservoir, and means for venting the reservoir including suitable passageways independent of the pump pressure space,- having valve means constituted by a port and a coacting control edge therefor on the cylinder and plunger respectively.

9. A fluid pump according to claim 8, in which fluid including any gas bubbles is bypassed from the'pump into the reservoir after the closing o'fithe inlet valve and before the beginning of discharge through the delivery outlet.

10. A fluid pump according to claim 8, having a non-return valve in the supply line to the reservoir. i g

11. A fluid pump according to claim 8, having a non-return and safety valve in the supply line to the reservoir.

i 12. In a fluid pump comprising a cylinder and part only of the volume of fluid displaced by the pump, a reservoir for fluid under pressure forming part of the supply line tothe pump from a low pressure source of supply, inlet and bypass-.

valve means between the pump pressure space and the reservoir, said inlet and bypass valve means being constituted by ports and coacting control edge therefor on the cylinder and plunger respectively, and valve venting means for the reservoir constituted by an additional port and coacting control edge therefor on the cylinder and plunger respectively.

13. A fluid pump according to claim' 12, in-

which the valve venting means, opens from the reservoir at a point higherthan the inlet and bypass valves open thereinto.

14. Ina fluid pump in, combination, a cylinder,

.a bypass port, both adapted to provide a path of flow between the pump pressure space and the reservoir, the bypass port opening from thatpart of the pressure space which is uppermost at a pointhigher than the inlet port and the said delivery outlet, whereby fluid and any air or gas bubbles in the cylinder are bypassed out from the uppermost part thereof, into the reservoir, after the closing of the inlet port and before pressure discharge through the loaded delivery valve, and means for venting the reservoir at a point higher than the inlet and bypass ports open thereinto, to relieve the reservoir of air or gas in excess of the capacity of that portion of the reservoir and communicating space above the said point at which the said valve venting means opens from the reservoir, said venting means in-' cluding an additionalport and coacting control edge therefor on the cylinder and plunger respectively.

l5. 'I'he'combination according to claim 14 in which the venting means including an additional port and coacting control edge, therefor on 17. In a plunger pump for the pressure discharge of a predetermined but variable quantity of fluid through a delivery outlet, a pump cylinder, 8. plunger in the cylinder, a reservoir surrounding the cylinder, an inlet valve for the flow of fluid into the cylinder, a bypass valve forthe flowof fluid including any air or gas bubbles from tlie uppermost -part of the pump pressure space into the-reservoir on the delivery stroke after, the closing of the inlet valve, means for opening and closing the said valves at' variable points relative to the stroke of the plunger, the

closing of the bypass valve controlling the beginning of discharge through the delivery outlet, and the inlet valve closing earlier as the bypass valve is closed earlier, whereby the quantity bypassed through the bypass valve is not reduced as the beginning 01' discharge is made earlier, the reservoir having a resilient capacity expansible under pressure and being provided with valve means whereby on each delivery stroke of the plunger and. before the beginning of discharge, the fluid bypassed builds up a suitable pressure ,in the reservoir intermediate of the supply and discharge pressures, said pressure being maintained in the reservoir during the period of discharge through the delivery outlet,

and a valve with controlling means therefor to relieve the pressure in the reservoir and to vent the reservoir of air or gas in excess of a definite quantity, at a suitable point in the stroke of the pump.

18. In a plunger pump having a delivery outlet for the high pressure discharge of a part only of the volume of fluid displaced by the pump, a reservoir for fluid under pressure forming part of the supply line to the pump from a low pressure source of supply, said reservoir having a. resilient capacity expansible under pressure, inlet and bypass valve means between the pump pressure space and the reservoir, a part of the pump charge including any air or gas bubbles, being bypassed from the pump pressure space into the reservoir on the discharge stroke of the pump before the beginning of high pressure discharge through the delivery outlet, and means whereby during a desired phase in the cycle of operation of the pump the reservoir is maintained at a suitable pressure stage intermediate of the supply and discharge pressures, said means including a non-return valve in the supply line to the reservoir, and valve means opening at another phase in the cycle of operation of the pump for venting the reservoir of any air or gas bubbles separating out from the fluid in the system and rising to the uppermost part of the reservoir, in excess of the capacity of that portion of the reservoir and communicating space above the point atwhich the valve venting means opens from the reservoir.

19. A fluid pump according to claim 18, in which the reservoir is maintained at a suitable pressure stage intermediate of the supply and discharge pressures during the period in which the high pressure of discharge through the delivery outlet is developed, whereby the leakage of fluid at high pressure between the plunger and its cylinder is reduced by the reduced pressure differential on the inside and outside of the cylinder walls.-

20. A fluid pump according to claim 18, 'in

which the valve means for venting the reservoir is opened at the end of the suction stroke of the pump, whereby the reservoir is maintained at a suitable pressure stage intermediate of the supply and discharge pressures during the suction stroke of the pump, and a more rapid filling of the pump when the pressure in the reservoir exceeds a certain maximum less than the pressure of discharge from the pump.

23. In a fluid pump in combination, a cylinder, a plunger cooperative therewith as a pump for high pressure discharge of fluid from the cylinder through a delivery outlet provided with a loaded delivery valve, a closed fluid reservoir forming part of the supplyline to the pump from a low pressure source of supply, coacting ports and control edges therefor on the cylinder and u plunger respectively, including an inlet port and a bypass port, both adapted to provide a path of flow between the pump pressure space and the reservoir, the bypass port opening from that part of the pressure space which is uppermost at a point higher than the inlet port and the said delivery outlet, whereby fluid and any air or gas bubbles in the cylinder are bypassed out from the uppermost part thereof, into the reservoir, after the closing of the inlet port and before pressure discharge through the loaded delivery valve,

means for venting the reservoir at a point higher than the inlet and bypass ports open thereinto, to relieve the reservoir of air or gas in excess of the capacity of that portion of the reservoir and communicating space above the said point at which the said valve venting means opens from the reservoir, said venting means including an additional port and coacting control edge therefor on the cylinder and plunger respectively, and

a non-return and safety valve in the supply line to the reservoir.

24. The combination according to claim 23 in which the venting means including an additional port and coacting control edge therefor on the cylinder and plunger respectively, are'so. arranged and disposed that the reservoir is vented. when the plunger is at the end of itssuction stroke.

25. The combination according to claim 23 in which the venting means including an additional port and coacting control edge therefor on the cylinder and plunger respectively, are so arranged and disposed that the reservoir is vented when the plunger is at the end of its discharge stroke.

' ARTHURJFIELDEN.

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