US2704035A

US2704035A - Injection pump for dual fuel engine

Info

Publication number: US2704035A
Authority: US
Inventors: Gerald L Bader
Original assignee: Nordberg Manufacturing Co
Current assignee: Nordberg Manufacturing Co
Priority date: 1948-05-06
Filing date: 1948-05-06
Publication date: 1955-03-15
Anticipated expiration: 1972-03-15

Description

March 15, 1955 BADER 2,704,035

INJECTION PUMP FOR DUAL FUEL ENGINE Filed May 6, 1948 5 Sheets-Sheet 1 Fly] In 06% for er a/d Z. ,Bader March 15, 1955 G. L. BADER INJECTION PUMP FOR DUAL FUEL ENGINE 3 Sheets-Sheet 2 Filed May 6, 1948 J vefizaz" @erald .Z. ,Bader Wm .lzfarieeys March 15, 1955 G. BADER INJECTION PUMP FOR DUAL FUEL ENGINE 3 Sheets-Sheet 3 Filed May 6, 1948 United States Patent INJECTION PUMP FOR DUAL FUEL ENGINE Gerald L. Bader, St. Louis, Mo., assignor to Nordberg Manufacturing Company, Milwaukee, Wis., a corporation of Wisconsin Application May 6, 1948, Serial No. 25,355

13 Claims. (Cl. 103-41) My invention relates to improvements in fuel injection control means for dual fuel engines and has for one object to provide fuel injection means which will be accurate through a very wide range.

My invention is especially directed to fuel control means for dual fuel engine of the compression ignition type wherein both liquid fuel and gas are used interchangeably and in cooperation and wherein the engine may sometimes be caused to burn only liquid fuel and other times be operated on gas and liquid fuel together.

The reason for such simultaneous use of gas and oil is that in a compression ignition engine, in order to insure positive ignition when burning gas, it is desirable to use a small amount of pilot liquid fuel because compression ignition of liquid fuel is more accurate and reliable than is compression ignition of gas fuel.

The result of this requirement is that the engine must have fuel injection control means which will be accurate through the entire working range for fuel oil operation and also accurate through the entire working range for pilot oil operation when a very much smaller amount of fuel oil is being used.

The fuel oil is preferably supplied to engine by a port controlled injection pump through a retraction valve and a spray nozzle, the pump, valve and nozzle being joined by conventional fuel piping. When fuel is supplied under pressure to the injection nozzle of a diesel engine, it is of the utmost importance that fuel be discharged only during the particular time range for which the engine and its injection mechanism has been designed and adjusted. The nozzle discharge should commence and should commence instantly at the time when the hydraulic pressure in the system reaches a predetermined point. That injection must continue from that point until the pressure in the system is lowered when injection must instantly stop. That means there must be no dribbling either at the beginning or at the end of the injection period. Injection must start instantly with substantially full volume and must end instantly; A pump is used which under the control of the various engine operating mechanisms builds up the pressure in the hydraulic system between the pump and the nozzle. When the proper amount of hydraulic fluid or fuel has been discharged by the pump, the pump pressure drops but because the system may be fairly long and because the walls of the piping are more or less flexible, means additional to the pump must be provided to make sure that injection takes place only during the proper timed interval. That is the function of the retraction valve and that is why retraction valves are habitually used in the industry. The retraction valve can be calibrated; it is not in the combustion chamber; it remains properly calibrated; it unseats when the pump pressure reaches the proper point; remains unseated during the time that the pump pressure remains above the predetermined point and the instant that the pump pressure falls below that point, the retraction valve closes to stop flow from the pump but also to retract enough of the hydraulic fluid in the system between the valve and the injection nozzle so that there will be no further flow of fuel in either direction, thus maintaining in the system a predetermined amount of fuel to insure that when the pressure is applied by the pump on the next injection cycle, operation will be instantaneously responsive to the pump.

One such retraction valve may be accurately adjusted or calibrated for the working range when oil only is being 2,704,035 Patented Mar. 15, 1955 used. Another such retraction valve may be accurately adjusted and calibrated for the pilot fuel oil range but when an effort is made to calibrate a single retraction valve to work accurately through both ranges, erratic delivery occurs.

In a dual fuel engine, two oil control problems appear. One is the control of the relatively large amount of oil injection to support engine operation when no gas is used. Under those circumstances, the injection system must control the amount of fuel oil from the range at which the engine will idle under no load up through the range of full load and overload. When on the other hand, the engine is burning gas, the injection system must control the relatively small amount of pilot liquid fuel which assists in ignition and that amount of pilot oil is far below the minimum amount of oil required for idling at no load when oil alone is used.

So we have the problem of controlling the oil flow in two totally separate ranges, the range of pilot oil plus gas operation and the range of oil only operation. As a general proposition, experience has indicated that it is very difficult, if not practically impossible, to accurately control oil injection-below twenty percent of the maximum capacity of a single hydraulic injection system and twenty percent of the maximum capacity is far above the capacity required at economical operation for the pilot phase of a dual fuel engine. My invention solves this problem because by the use of a dual retraction valve I am able in one hydraulic injection system to get proper control with a single pump and a single injection nozzle, of pilot injection for combined gas and oil fuel and injection for oil fuel alone.

I propose therefore to use in one and the same system, a pump calibrated for accuracy both in the high discharge range for full oil injection and in the low discharge range for pilot oil injection. This can be done, for instance, with a conventional type of port control pump by having a very long rack travel and a small slope angle of the helix provided such pump be associated with a dual retraction valve and I propose therefore, a retraction valve which preferably has one large spring seated main retraction valve member to handle oil supply when oil only is being burned and to mount on this main retraction valve, a smaller pilot retraction valve, which will function when oil and gas both are being burned.

Both valves are spring loaded so that when the pump is adjusted for pilot operation it will only furnish the relatively small amount of oil in a relatively narrow range necessary for pilot operation and control by the pilot valve. When the pump is operating to furnish all the oil fuel, it will furnish the wide range of oil in larger volume controlled by the main retraction valve. In addition, I propose to so arrange these two valves that when the main retraction valve opens, it catches up with the pilot valve so that what little fuel enters through the pilot valve at the beginning and end of the cycle of the main valve operation, will not adversely affect the operation of the engine.

My invention is illustrated more or less diagrammatically in the accompanying drawings, wherein:

Figure 1 is a longitudinal section through the retraction valve;

Figure 2 is a similar section of a modified form of the device;

Figure 3 is a diagrammatic illustration of the pump and spray nozzle assembly associated with the retraction valve.

Like parts are indicated by like characters throughout the specification and drawings.

I have not illustrated the pump because any suitable type, and there are many on the market, for port controlled pump or any other suitable type of pump, which may be calibrated through a sufficiently wide range of delivery will, when associated with my valve, give the results which I desire. The same is true of the injection nozzle, the details of which form no part of my present invention.

1 is a housing containing the retraction valves, 2 a valve cage shouldered at 3, socketed in the housing 1, containing an oil discharge passage 4 and threaded at 5 for connection with a suitable oil pressure line which leads to any suitable engine injection or spray nozzle not here illustrated. 6 is the pump barrel threaded or otherwise held as at 7 in the housing 1 forming part of any suitable standard port controlled injection pump not here illustrated in detail as the pump details form no part of my invention and many suitable pumps are available on the market.

8 is the main retraction or discharge valve guide socketed in the housing 1, flanged at 9 to engage the end of the sleeve 6 extending into the valve cage 2. 10 is a packing ring in the housing 1 compressed between the flange 9 and the sleeve 6 by the holding ring 11 which encircles the cage 2, engages the shoulder 3 and is held down against the packing ring 10 by the cap screws 12.

Slidable in the main valve guide 8 is the main retraction valve body 13. It has an enlarged valve head 14 seating on the chamfered valve seat 15 on the main valve guide 8. Radial passages 17 connect with the hollow interior 18 of the main valve body 13 to receive oil under pressure from the pump through the sleeve 6. The passages 17 are closed until the main retraction valve body is raised enough to bring them above the valve seat 15 but because this valve must be able to move freely toward and from its seat, working clearance is provided and under the pressures with which we are dealing, oil leakage can and will take place through this clearance. That oil leakage, however, will be small and when the valve head engages the seat 15, a positive closure is provided and such leakage is prevented.

The main valve head 14 is flanged at 19 to form a seat for the main valve spring 20 which at its other end, seats on the flange 21 of the main valve stop 22 in the valve cage 2 so that the main valve is held yieldingly on its seat by the pressure of the spring 20. The main retractor or discharge valve stop 22 is socketed in the valve cage 2 above the valve 13 and has the downwardly depending stop sleeve 23 adapted to be engaged by the valve head 14 to limit the upward excursion of the latter. Oil under pressure which lifts the valve 13 compressing the spring 20 may escape through the valve seat 15 into the valve cage 2 and thence through the radial passages 24 to the central aperture 25 in the stop 22 and then out through the discharge passage 4.

Slidable in the main body 13 is a pilot valve body 26 having a pilot valve head 27 seated on the seat 28 on the main valve 13 by a pilot valve spring 29 which engages the flange 30 on the pilot valve head 27 at one end and the flange 31 on the pilot valve stop 32 at the other end.

The pilot valve body 26 slides in the main valve body 14. It has a plurality of radial passages 34 communicating with the longitudinal passage 35 in the pilot valve body, which in turn communicates with the interior of the main valve body. These radial passages 34 are closed except when upward movement of the pilot valve with respect to the main valve brings those passages above the pilot valve seat 28. The purpose of the positive seating of the head 27 on the seat 28 to prevent flow of fuel oil through the clearance between the valve stem and its guide is the same in connection with the main valve.

Downward movement of either the main retraction valve or the pilot retraction valve or both continues after the radial passages have been closed. The valve heads displace a substantial volume in proportion to the volume of the hydraulic system between the valves and the spray nozzle and the downward movement of either or both the retraction valve heads after the radial passages have been closed, results in retracting enough of the hydraulic fluid in the system to insure that dribbling at the nozzle will be prevented and to insure that only a sufficient volume of fluid is contained within the system during the time of completion of one injection and the inauguration of the next.

The pilot valve stop 31 has a longitudinal aperture 36 communicating at one end with the discharge passage 34 through the aperture 25 in the main valve stop 22. This aperture 36 is open toward the pilot valve and has radial passages 37 extending therefrom to the interior of the main valve stop sleeve 23. The pilot valve 26 and all its associated parts are of such diameter as to be able to be contained within and penetrate into the main valve stop sleeve 23. When the parts are in the position shown in Figure 1 with both valves seated, the distance from each valve to its stop is as illustrated, substantially identical.

There is a substantial convenience in telescoping the pilot valve into the main valve. Each valve operates independent of the other. Each valve permits passage of that amount of oil under pressure for which it had been set and adjusted but if desired, the two valves could be arranged in parallel rather than in series and the operation would be to all intents and purposes, the same.

In the modified form shown in Figure 2, the two re traction valves are separately mounted and separately housed in parallel between the pump and the injection nozzle. For convenience I have shown the same type of pilot valve and main valve as is shown in Figure 1, though of course, both with respect to Figure l and Figure 2, any suitable type and there are many, of retraction valves may be used. I have shown the extent of linear movement of the two valves different in Figure 2 whereas in Figure 1, they are the same. Under some circumstances with either type or either arrangement, the valve movement might preferably be the same, under other circumstances it might preferably be different. That depends on the design of the pump and the desired operating characteristics.

When the two valves are separately mounted and sep arately housed, the peculiarity that the main valve which opens later than the pilot valve may catch up with the pilot valve and in effect closes it, disappears. Under these circumstances, unless additional manipulation takes place. there will always be flow through the pilot superposed on the flow through the main valve and so since under some circumstances this might not be desirable, I have shown manually controlled means for positively closing either or both of these valves. This manual control means is purely diagrammatic and it might be controlled in consonance with other elements of engine control under which circumstances the mechanical connection between the means for positively setting the valves and the engine control mechanism, I would have by mechanical means the same automatic effect, the same automatic operation that I obtain by hydraulic means in the device of Figure 1.

50 is a pump plunger mounted for reciprocation in the pump barrel 6. It is driven by any suitable means as by a cam, a crank or a lever, as the case may be, to cause it to reciprocate toward and from the retraction valve. 51 is a fuel oil chamber in the housing 1 surrounding the pump barrel 6. It is supplied with fuel oil by any suitable means through the pipe 52. 54 is an induction port between the fuel oil chamber 51 and the interior of the pump barrel 6 through which, when the pump plunger 50 is retracted, oil may enter and fill the pump barrel. 55 is a control groove in the plunger 50 having a helical upper wall 56 and a lower wall 57 perpendicular to the axis of the plunger. A passage 58 in the periphery of the plunger is out of line with the port 54 and extends from the groove 55 to the end of the plunger. 59 is a gear keyed to the barrel 6. 61 is a rack in mesh with the gear which may be moved laterally to rotate the gear and so rotate the barrel. As the plunger moves down, the pump barrel 6 above it fills with oil; as it moves up, the port 54 is closed, the upward movement of the plunger forces fuel oil through the retraction valve, and this continues until the control groove 55 comes in register with the port 54 at which time pump pressure is relieved, the remaining plunger movement may continue without further movement of oil through the retraction valve, the oil escaping through the passage 58, the groove 55 and the port 54, back into the fuel oil chamber 51. The rotation of the barrel 6 under the influence of the rack, the plunger 50 not rotating, changes the time when the helical upper wall 56 reaches the lower portion of the port 54 so that in the position shown, pressure relief is early. As the plunger is rotated in a clockwise direction looking down, the time of release will be retarded and the amount of oil supplied to the engine increases. 62 is a spray nozzle connected by the oil pressure line 63 to the retraction valve housing.

It will be realized that whereas I have illustrated and described an operative device, still many changes might be made in the size. shape, arrangement and number of parts without departing materially from the spirit of my invention. I wish, therefore, that my showing be taken as in a sense diagrammatic and illustrative rather than as limiting me to the precise showing.

1 The use and operation of my invention are as folows:

In both of the illustrative forms that I have shown, the retraction valves are in communication with the pump, the discharge from which may be controlled by the engine governor for the supply of fuel oil in large volume and high pressure to support engine operation on oil alone or to supply a relatively smaller volume of oil at perhaps somewhat lower pressure for pilot injection when gas and oil are burned together. The pump itself is therefore calibrated and arranged to discharge a controlled proper amount of oil in both working ranges, that is in the pilot range and in the range of only oil burnmg.

The engine as it operates, operates the pump. The governor in the usual manner controls the pump operation in consonance with variations in the load or speed as the case may be. Every pump reciprocation builds up pressure in the hydraulic injection system. The hydraulic fluid, that is the fuel, discharges through the injection nozzle into the combustion chamber. The injection nozzle is in the usual well-known manner set so that its valve only opens when a predetermined pressure level has been reached in the hydraulic injection system and no matter what variation there may be in the pressure in the system, the injection valve will not open and should not discharge fuel until the hydraulic pressure in the system has reached and exceeded the pressure at which the nozzle is set to open.

The governor controls pump discharge in consonance with the varying demands of the engine both in the pilot range where oil and gas together are being burned and in the range where only oil is being burned. The pressure in the hydraulic system is a function of pump-piston position, pump-piston movement, discharge from the system into the engine and by-pass discharge from the pump so that as the pump starts its pressure stroke, pressure builds up in the system.- First the pressure reaches a point at which the pilot retraction valve opens. If the volume of fuel discharged by the pump under those circumstances is small enough, only the pilot retraction valve will open and the pressure will increase to a point at which the predetermined'amount of pilot fuel is discharged by the injection nozzle. If, on the other hand, a larger quantity of fuel is discharged by the pump into the hydraulic system, the opening of the small relatively light, relatively low capacity pilot valve will be followed usually almost instantly by opening of the larger capacity main retraction valve. This will result in the main valve catching up with the pilot valve if one is mounted on the other as in the preferred form and during the remainder of the discharge of pump capacity into the injection system,

all flow will be through the main valve. As soon as the pressure drops as a result of pump operation and control below the pressure required to open the main valve, that valve closes and immediately thereafter, perhaps even simultaneously therewith, the main valve closes. Both valves as they close, first cut olf fuel travel through the radial passages in the two valve bodies and tllien after flow has been cut olf, they seat to positively c ose.

Because of the necessity of clearance to permit proper valve operation, there may well be a certain amount of leakage through the valves even after the valve ports have been closed but that leakage will be so small relatively to the volume displaced by the retraction valve that retraction nevertheless take place up to the point when the retraction valve seats to positively close the valve and positively stop any discharge of fuel through the valve.

The pump at each injection stroke builds up oil pressure. The relatively weak pilot valve spring will first be compressed and the lighter smaller pilot valve will be raised from its seat by the oil. If the pump has been controlled by the governor or otherwise to work in the pilot range, then the relatively small amount of oil will be adequately passed by the pilot valve and there will be no reason for and no tendency for the main valve to be opened.

If, on the other hand, the pump has been controlled to operate in that range in which only oil is burned, much larger quantities of oil will be discharged by the pump and so as soon as the pump pressure builds up to the desired point, the pilot valve will be unseated but because of the larger amount of oil furnished, perhaps at higher pressure, the pilot valve will not be of sufiicient capacity "and so the main valve will immediately open. It will normally catch up with the pilot valve almost instantaneously and the pilot valve will thus be closed and oil to support combustion without gas will be discharged through the main valve.

As soon as the proper amount of oil has been dis charged by the pump, the pressure drops and then first the main valve closes and immediately thereafter the pilot valve closes and the retraction characteristics of the two valves or of the pilot valve alone if only the pilot valve has opened, will be sufficient to reverse the movement of the fuel in the system so as to prevent dribbling and at the same time leave the system full of oil ready to be injected at the next pump stroke.

Under these circumstances while it is true that there may be a slight movement of oil through the pilot valve at the beginning and at the end of the main working injection stroke, such oil movement will be so small as to be relatively unimportant and may be easily compensated for by the adjustment of the parts.

In the form shown where the retraction valves are in parallel, the operation will be the same except that under these circumstances unless special means are used to close one or the other of the valves and hold it closed and independent of hydraulic pressure, there would always be a certain amount of oil passing through the pilot valve during the entire injection stroke which amount would be superposed on and be in addition to the amount passing through the main retraction valve but such amount will be compensated for and taken care of by the adjustment of the control element.

If manual means are used to positively seat the valves, then the operator when he switches over from operation only on oil to operation on oil and gas, he would positively close the main valve leaving the pilot retraction valve free to operate. When he switches back to oil, he will positively close the pilot retraction valve and release the main valve or if desired, a mechanical connection may be interposed between the two positive valve seating means and the control lever or other mechanism, Whatever it may be, which changes from oil to oil and gas operation, in which case a single manipulation will automatically control by mechanical means the operation of the two valves so that whichever retraction valve is desired will be free to operate in consonance with the other engine control elements.

In this connection it should be remembered that a very small increment of time is involved in connection with this entire process and also a very much smaller increment of time is involved at each end of the movement of the big main valve so that the effect of the pilot valve in relation to the effect of the main valve, whether they are in series or in parallel is negligible and this would be true even in the case where the parts were adjusted either in series or parallel to allow the two valves to remain open throughout the entire injection period.

I claim:

1. In a fuel injection system of the type including a pump adjustably operable to supply predetermined metered amounts of fuel under high pressure at each stroke and to release the high pressure abruptly upon delivery of said metered amounts, the combination of discharge valve means comprising a pair of valves connecting the high pressure side of said pump to the fuel line of said system, each of said valves including retraction means for withdrawing fuel from said fuel line during closing movement of said valves, stop members for limiting the opening movement of each of said valves, and individual spring means of different stiffness for resisting opening movement of said valves, whereby the opening of said valves and the amount of fuel withdrawn from said fuel line by said retraction means is dependent upon variations in the metered amounts of fuel supplied by said pump.

2. In a fuel injection system of the type including a pump adjustably operable to supply predetermined metered amounts of fuel under high pressure at each stroke and to release the high pressure abruptly upon delivery of said metered amounts, the combination of discharge valve means connecting the high pressure side of said pump to the fuel line of said system and comprising a pair of valves one of which opens under a lesser pressure than the other, each of said valves including retraction means for withdrawing a predetermined amount of fuel from said fuel line during closing movement thereof.

3. In a fuel injection system of the type including a pump adjustably operable to supply predetermined metered amounts of fuel under high pressure at each stroke and to release the high pressure abruptly upon delivery of said metered amounts, the combination of discharge valve means comprising a first valve connecting the high pressure side of said pump to the fuel line of said system and including a valve member having a central passageway therethrough, and a second valve disposed in said passageway and including a second valve member, each of said valve members including retraction means for withdrawing fuel from said line during closing movement thereof, and individual spring means of different stiffness for efiecting closing movement of said valve members.

4. In an injection system for diesel engines and the (ike, a pressure chamber, a main inlet duct communicating therewith, a main valve body slidable in the duct and having a valve head projecting into the chamber, a valve seat in the chamber encircling the duct, yielding means adapted to bias the main valve body away from the chamber and the valve head toward the seat, the main valve body being adapted to permit flow through the valve seat, only, during such time as the main valve head is raised a substantial distance above the seat, the main valve body being centrally apertured in communication with the duct and the chamber. a pilot valve body slidable in said aperture having a valve head projecting into the chamber, a valve seat on the main valve, in the chamber, encircling the aperture, yielding means adapted to bias the pilot valve body away from the chamber and the pilot valve head toward the seat, the pilot valve body being adapted to permit fiow through its valve seat, only, during such time as the pilot valve head is raised a substantial distance above its seat.

5. In an injection system for diesel engines and the like, a pressure chamber, a main inlet duct communicating therewith, a main valve body slidable in the duct and having a valve head projecting into the chamber, a valve seat in the chamber encircling the duct, yielding means adapted to bias the main valve body away from the chamber and the valve head toward the seat, the main valve body being adapted to permit flow through the valve seat, only, during such time as the main valve head is raised a substantial distance above the seat, a pilot inlet duct communicating with the pressure chamber, a pilot valve body slidable in the pilot inlet duct, having a valve head projecting into the chamber, a valve seat in the chamber encircling the pilot duct, yielding means adapted to bias the pilot valve body away from the chamber and the valve head toward its seat, the pilot valve body being adapted to permit flow through its valve seat only during such time as the pilot valve head is raised a substantial distance above its seat.

6. In an injection system for diesel engines and the like, a pressure chamber, a main inlet duct communicating therewith, a main valve body slidable in the duct and having a valve head projecting into the chamber, a valve seat in the chamber encircling the duct, yielding means adapted to bias the main valve body away from the chamber and the valve head toward the seat, the main valve body being adapted to permit flow through the valve seat, only, during such time as the main valve head is raised a substantial distance above the seat, the main valve body being centrally apertured in communication with the duct and the chamber, a pilot valve body slidable in said aperture having a valve head projecting into the chamber, a valve seat on the main valve, in the chamber, encircling the aperture, yielding means adapted to bias the pilot valve body away from the chamber and the pilot valve head toward the seat, the pilot valve body being adapted to permit flow through its valve seat, only, during such time as the pilot valve head is raised a substantial distance above its seat, stop means rigidly mounted in the chamber for separately limiting the movement of both valves away from their seats.

7. In an injection system for diesel engines and the like, a pressure chamber, a main inlet duct communicating therewith, a main valve body slidable in the duct and having a valve head projecting into the chamber, a valve seat in the chamber encircling the duct, yielding means adapted to bias the main valve body away from the chamber and the valve head toward the seat, the main valve body being adapted to permit flow through the valve seat, only, during such time as the main valve head is raised a substantial distance above the seat, a

pilot inlet duct communicating with the pressure chamber, a pilot valve body slidable in the pilot inlet duct, having a valve head projecting into the chamber, a valve seat in the chamber encircling the pilot duct, yielding means adapted to bias the pilot valve body away from the chamber and the valve head toward its seat, the pilot valve body being adapted to permit flow through its valve seat, only, during such time as the pilot valve head is raised a substantial distance above its seat, stop means rigidly mounted in the chamber for separately limiting the movement of both valves away from their seats.

8. In an injection system for diesel engines and the like, a pressure chamber, a main inlet duct communicating therewith, a main valve body slidable in the duct and having a valve head projecting into the chamber, a valve seat in the chamber encircling the duct, yielding means adapted to bias the main valve body away from the chamber and the valve head toward the seat, the main valve body being adapted to permit flow through the valve seat, only, during such time as the main valve head is raised a substantial distance above the seat, the main valve body being centrally apertured in communication with the duct and the chamber, a pilot valve body slidable in said aperture having a valve head projecting into the chamber, a valve seat on the main valve, in the chamber, encircling the aperture, yielding means adapted to bias the pilot valve body away from the chamber and the pilot valve head toward the seat, the pilot valve body being adapted to permit flow through its valve seat, only, during such time as the pilot valve head is raised a substantial distance above its seat, stop means rigidly mounted in the chamber for separately limiting the movement of both valves away from their seats, the stop members being so related that when the main valve engages its stop, the pilot valve is seated on its seat.

9. In an injection system for diesel engines and the like, a pressure chamber, a main inlet duct communicating therewith, a main valve body slidable in the duct and having a valve head projecting into the chamber, a valve seat in the chamber encircling the duct, yielding means adapted to bias the main valve body away from the chamber and the valve head toward the seat, the mainvalve body being adapted to permit flow through the valve seat, only, during such time as the main valve head is raised a substantial distance above the seat, the main valve body being centrally apertured in communication with the duct and the chamber, a pilot valve body slidable in said aperture having a valve head projecting into the chamber, a valve seat on the main valve, in the chamber, encircling the aperture, yielding means adapted to bias the pilot valve body away from the chamber and the pilot valve head toward the seat, the pilot valve body being adapted to permit flow through its valve seat only during such time as the pilot valve head is raised a substantial distance above its seat, each valve body as it moves toward its valve seat from the chamber being adapted to increase the volumetric capacity of the chamber.

10. In an injection system for diesel engines and the like, a pressure chamber, a main inlet duct communicating therewith, a main valve body slidable in the duct and having a valve head projecting into the chamber, a valve seat in the chamber encircling the duct, yielding means adapted to bias the main valve body away from the chamber and the valve head toward the seat, the main valve body being adapted to permit flow through the valve seat, only, during such time as the main valve head is raised a substantial distance above the seat, a pilot inlet duct communicating with the pressure chamber, a pilot valve body slidable in the pilot inlet duct, having a valve head projecting into the chamber, a valve seat in the chamber encircling the pilot duct, yielding means adapted to bias the pilot valve body away from the chamber and the valve head toward its seat, the pilot valve body being adapted to permit flow through its valve seat only during such time as the pilot valve head is raised a substantial distance above its seat, each valve body as it moves toward its valve seat from the chamber being adapted to increase the volumetric capacity of the chamber.

ll. In an injection system for diesel engines and the like, a pressure chamber, a main inlet duct communicating therewith, a main valve body slidable in the duct and having a valve head projecting into the chamber, a valve seat in the chamber encircling the duct, yielding means adapted to bias the main valve body away from the chamber and the valve head toward the seat, the main valve body being adapted to permit fiow through the valve seat, only, during such time as the main valve head is raised a substantial distance above the seat, the valve body as it moves toward its valve seat from the chamber being gdapted to increase the volumetric capacity of the cham- 12. In an injection system for diesel engines and the like, a pressure chamber, a main inlet duct communicating therewith, a main valve body slidable in the duct and having a valve head projecting into the chamber, a valve seat in the chamber encircling the duct, yielding means adapted to bias the main valve body away from the chamber and the valve head toward the seat, the main valve body being adapted to permit flow through the valve seat, only, during such time as the main valve head is raised a substantial distance above the seat, the main valve body being centrally apertured i-n communication with the duct and the chamber, a pilot valve body slidable in said aperture having a valve head projecting into the chamber, a valve seat on the main valve, in the chamber, encircling the aperture, yielding means adapted to bias the pilot valve body away from the chamber and the pilot valve head toward the seat, the pilot valve body being adapted to permit flow through its valve seat, only, during such time as the pilot valve head is raised a substantial distance above its seat, the pilot valve body being smaller than and being adapted to permit the passage of a lesser amount of fluid than the main valve body.

13. In an injection system for diesel engines and the like, a pressure chamber, a main inlet duct communicating therewith, a main valve body slidable in the duct and having a valve head projecting into the chamber, a valve seat in the chamber encircling the duct, yielding means adapted to bias the main valve body away from the chamber and the valve head toward the seat, the main valve body being adapted to permit flow through the valve seat, only, during such time as the main valve head is raised a substantial distance above the seat, a pilot inlet duct communicating with the pressure chamber, a pilot valve body slidable in the pilot inlet duct, having a valve head projecting into the chamber, a valve seat in the chamber encircling the pilot duct, yielding means adapted to bias the pilot valve body away from the chamber and the valve head towards its seat, the pilot valve body being adapted to permit flow through its valve seat only during such time as the pilot valve head is raised a substantial distance above its seat, the pilot valve body being smaller than and being adapted to permit the passage of a lesser amount of fluid than the main valve body.

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