US1868498A

US1868498A - Pump

Info

Publication number: US1868498A
Application number: US285273A
Authority: US
Inventors: Lloyd B Gruman
Original assignee: Individual
Current assignee: Individual
Priority date: 1928-06-14
Filing date: 1928-06-14
Publication date: 1932-07-26
Anticipated expiration: 1949-07-26

Description

July 26, 1932. B. GRUMAN PUMP Filed June 14, 1928 5 Sheets-Sheet l [III/{765070.

' .Gr armro v L. B. GRUMAN 1,868,498

PUMP

Filed June 14, 1928 5 Sheets-Sheet 2 July 26, 1932.

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| B. GRUMAN PUMP Filed June 14, 1928 5 Sheets-Sheet 3 July 26, 1932. I L, B GRUMAN 1,868,498

PUMP

Filed June 14, 1928 5 Shets-Sheet 4 Zlo Kalb. (ir Lunan- ZE LSHEFO 016% @9 QWMAQ:

Patented July 26, 1932 PATENT OFFICE LLOYD B. GBUMAN, OF NEWARK, NEW JERSEY Application filed June 14,

This invention relates to reciprocating pumps, its principal object being to provide a compact and eflicient pump whereby variable pressures and capacities can be attained,

at constant speed, within the rated horsepower of the prime mover.

Another object of the invention is to provide a pump which is operable at extremely high or low pressures governed by high and low pressure by-pass valves which are arranged in co-operative relation to the high and lower pressure elements of the pump and are automatically operable under the influence of fluid pressure.

Another object of the invention is to provide novel power transmitting means whereby the stroke of the pump can be adjusted at will, from zero to maximum, and this when the pump is either activeor idle, thereby not only affording provision for a wide range of pressures and capacities, but also enabling the easy progressive starting of the pump under heavy pressures, thus minimizing the wear and tear on the pump parts.

35 With these and other objects in view my invention comprises novel features of construction and combinations of elements which, in a preferred embodiment of my invention, will be hereinafter described; the scope of the invention then being defined in the appended claims.

In the drawings- Figure 1 is a longitudinal horizontal section, partly in plan, of a duplex pump embodying my invention.

Fig. 2 is a longitudinal vertical section, as on the line 22 of Fig. 1.

Fig. 3 is a transverse vertical on the line 3-3 of Fig. 2.

Fig. 4 is an elevation of the left end of the pump as viewed in Fig. 2.

Figs. 5 and 6 are transverse vertical sec-' tions, as on the lines 5-5 and tively, of Fig. 4. Fig. 7 is a transverse vertical section, as on the line 7-7 of Fig. 1.

Fig. 8 is a partial side elevation ton stroke adjustin mechanism.

The invention is lierein illustrated as embodied in a pump of the duplex type compris- 66, respecof the pissection, as'

1928. Serial No. 285,273.

ing spaced-apart units, A, B, whereof the respective pistons are in axial alignment and are operatively connected to a common drive shaft 10 through intermediate transmitting mechanism of such construction that, amongst other important advantages, the stroke of the pistons can be readily adjusted within limits to effect wide ranges of pressures and capacities, at constant speed, as will be hereinafter described.

Since the pump units are identical in construction and operation, save that their respective pistons operate in alternation with respect to the intake and discharge of the liquid, a descriptionof one unit will suflice. Each pump unit comprises a suitable casing 11 in which are formed two concentric cylindrical chambers constituting low and hi h pressure chambers 12, 13, respectively, in which two concentric

cylindrical pistons

14, 15, of different diameters, are mounted to reciprocate. The outer piston 14 constitutes a low-pressure piston and the inner or central piston 15 constitutes a high-pressure piston. The low-pressure piston consists of a hollow cylinder slidably fitted within packing glands 16 contained in the cylinder constituted by the casing, which glands support between them suitably-disposed packing rings 17 surrounding the piston. One end of this piston extends outwardly beyond the adjacent end of the casing and is headed, as at 18, the head being screwed, as at 19, or otherwise connected, to a reciprocating yoke or cross-head 190 included in the aforementioned adjustable stroke transmitting mechanism.

The packing rings 17 are preferably leather cups, U-form in cross-section, having their open ends opposite to and spaced from each other, as shown, to provide a chamber wherein the pressure equals the maximum pressure produced by the low-pressure piston, thus in conjunction with the glands 16, ensuring an eflicient seal for the outer wall of the piston 14.

The high pressure piston 15, whichis of smaller diameter and greater length than the iston 14, extends centrally of the latter, and i s screwed or otherwise fixed at one end to the head 18, so that the two pistons are simultaneously movable in the same direction. That end'of the piston adjacent the head 18, is provided with radial ports 20, and the opposite open end is equipped with a suction valve 21 which is" normally held to its seat by the action of a suitable spring 22 interposed between the valve and a ring 23 fast on the adjacent end of the piston 15. This piston is reciprocable in and longitudinally of a cylinder 24 which is threaded into a head 25 bolted to the adjacent end of the casing 11, said cylinder 24 bein concentric to the internal cylindric wall 0% the casing. The cylinder 24 is provided with suitable packing 26 for per portion of the delivery end of the piston 15, which packing is held in place by an adjustable gland 27. The cylinder head 25 has formed therein in axial alignment with the high pressure chamber 13 a chamber 28 which is closed at the outer wall of the head 25 bymeans of a screw cap 29. The chamber 28 thus constitutes the delivery end of the high pressure chamber. By removing the cap 29 access can be readily had to the packing gland 27 and valve 21 :as need may require.

In the head 25 aretwo spaced-apart vertical valve chambers 30, 31 opening at their lower ends into vertical passages 32 which are connected'by a by-pass 33. This lby-pass communicates, directly below the chamber 30, with a suction port 34 into which leads a pipe 35 from a suitable source of liquid supply. The lower portion of the chamber 30 is annularly recessed,-as at 36, and the annular chamber thus formed communicates through a port 37 in the casing with the upthe lowpressure chamber 12. (See Fig. 5.) Likewise the lower portion of the chamber 31 is annularly recessed, as at 38, and the annular chamber thus formed is-in lateral communi cation with the chamber 28 at the delivery end of the high-pressure chamber. (See Fig. 3.) I Vertically reciprocable in the chambers 30, 31 are

valves

39, 40, respectively, the valve 39 constituting an automatic low pressure bypass valve, and the valve 40 constituting an automatic high pressure by-pass valve.

The low pressure by-pass valve comprisw a hollow cylindrical body seated in the chamber 30 at or below the bottom of the annular chamber 36, and provided at its lower end head 25, between with a port 41 which opens into the adjacent lower passage 32 and contains a suction valve 42. The by-pass valve 39 is provided with radial ports 43 which establish communication between the port 41 and the annular chamber 36 when such by-pass valve is seated.

The valve 39 is also provided with upper radial ports 44 which communicate with a-- discharge port 45 formed in the cylinder the two chambers 30, 31. An outlet valve 46 is seated in the body of the by-pass valve, below the radial ports 44.

" prises When the by-pass valve 39 is bodily raised communication between the annular chamber 36 and the adjacent vertical passage 32 is established at the valve seat.

The upper end of the by-pass valve 39 is provided containing packing 48 through which centrally extends a vertically-sliding trip pin 49 the foot of which is exposed to the fluid pressure above the outlet valve 46. This pin rises into a gland 50 screwed into the bonnet so as to bear upon the packing which encircles and seals the pin. The gland is formed with an upstanding yoke 51 which loosely embraces an arm 52 that is fulcrumed, as at 53, on a suitably disposed post 54 on the cylinder head 25. A relatively light spring 92 encircling the upper portion of the valve and bearing against the head 25 and the flange of the bonnet 47 tends to maintain the yoke in contact with the arm 52. The arm has hung thereon a weight 55 which is adjustable longitudinally of the arm so as to regulate the pressure required on the foot of the trip pin to raise the weighted arm and permit the ascent of the by-pass valve 39, as will presently appear.

The high pressure by-pass valve 40 coma hollow cylindrical body headed at its lower end and seated in the chamber 31, at or below the bottom of the annular chamber 38. This body is provided adjacent the chamber with radial ports 56 which are so located that when the valve 40 is seated communication is established between the chamber 38 and the interior of the by-pass valve 40, and that when such by-pass valve is raised from its seat communication between the chamber 38 and the adjacent vertical passage 32 is established at the valve seat. The valve body is formed with upper radial ports 58 below which is seated in the contained valve body an outlet valve 59. These ports 58 communicate with the adjacent discharge port 45 formed in the cylinder head 25.

' The upper end of the high pressure bypass valve is provided, similarly to the low pressure by-pass valve, with a suitable screw bonnet 470; a central sliding trip pin 490, a gland 500, and packing 480 and a spring 93. The gland is also formed with a yoke 510 which loosely embraces an arm 520, fulcrumed on a post 540 and having a suitable weight 550 which is adjustable longitudinally of the arm so as to regulate the pressure required on the trip pin to raise the weighted arm and permit the ascent of the by-pass valve 40.

The wall of each of the by-pass valve chambers, (30, 31) has formed therein, in the region of the upper radial ports of the contained by-pass valve, an annular recess 60 which communicates with the discharge port 45. Within the recess are confined packing rings 61 which encircle and bear against the with a suitable screw bonnet 47 v It is to be noted that the by-pass valves" 39,40 and their appurtenances may be removed from the cylinder head by simply removing the respective weight arms.

The cycle of the flow of liquid through each pump unit for one revolution of the drive shaft is as follows: As the

hollow pistons

14, 15, move toward the cylinder head 25 on the discharge stroke of the pump, the suction valve 21 of the high pressure piston 15 is closed and held to its seat. So also the suction valve 42 of the low pressure bypass valve-39 is seated. The liquidin the low pressurechamber 12, equal to the displacement of the low pressure piston 14, is forced through the port 37'into the annular chamber 36 and through the radial ports 43 of the lowpressure by-pass valve 39, passing thence into the latter above the suction valve 42. This liquid, under pressure, raises the outlet valve 46 of the by-pass valve 39 and passes through the radial. ports 44 into the discharge port 45. At the same time, the liquid in the high-pressure chamber 13, equal to the displacement of the high pressure piston 15, is forced through the chamber 28 into the annular chamber 38 and through the radial ports 56 of the high pressure by-pass valve, into the latter. Coincidentally the pressure of the liquid raises the outlet valve 59 and therefore the liquid under pressure passes through theradial ports 58 into the discharge port 45.

In the return or suction stroke of the pump, the suction valve 21 of the high pressure piston is open and likewise the suction valve 42 of theby-pass valve 39, thus causing the liquid to flow through the suction ort 34 which is connected to the source 0 liquid supply. This liquid flows past the open suction valve 42 and through the ports 43 and annular chamber 36. into the low-pressure chamber 12. The liquid passes thence through the ports 20 into the interior of the piston 14 and past the open'valve 21 into the high-pressure chamber 13.

It isto be noted that any air that may collect in the pressure chambers 12, 13 will be discharged through the common suction port 37 which is located at the top of the low pressure chamber. I It is also to be noted that the piston packing, as well as the pistons, is surrounded by flowing liquid, which preventsthe overheating of the packing and pistons by friction, thus protecting the packing and the surface of the pistons and prolonging the efficient life of the pump.

The automatic by-pass valves'hereinbefore' described are normally maintained on their respective seats by the adjustable weight connections, the respective weights being adjusted on their arms to meet predetermined pressure requirements. For example, assuming that it be required to cut out the low pressure pump at 100 lbs. and the high pressure pump at 2000 lbs., the weight 55 on the arm 52, which is associated with the low pressure bypass valve 39, is set a suificient distance from the fulcrum 53 to counterbalance the lifting force exerted on the trip pin 49 by a pressure of 100 lbs. in the discharge port 45 plus the force of the spring 92; and the weight 550 on the arm 520, which is associated with the high pressure by-pass valve 40, is set to counterbalance the lifting force exerted on the trip pin 490 by a pressure of 2000 lbs. in the discharge port plus the force of the spring 93.

The weights having been adjusted as just mentioned, the operation is as follows: When the pump pressure exceeds 100 lbs. the trip pin 49 is moved upward against the arm 52, by the fluid pressure against the foot of the pin. Thus the arm is raised, and the spring 92, expanding, raises the valve bodily from its seat until the arm reaches the bottom of the slot in post 54. The trip pin 49 has a longer stroke than the arm 52, and hence the pin maintains its pressure against the arm, thus permitting the spring 92 to hold the by-pass valve from its seat until the pressure in the discharge port falls below 100 lbs. The valve 46 closes and remainsclosed on the discharge stroke of the pump, and hence the liquid is allowed to by-pass from the annular chamber 36 into the passage 32 and back to the suction port 34 instead of flowing into the by-pass valve and past the valve 46.

Then the pump pressure exceeds 2000 lbs. the trip pin 490is moved upward against the v arm 520 by the fluid pressure against the foot .has a longer stroke than the arm 520, and

hence the pin maintains its pressure against the arm, thus permitting the spring 93 to hold the by-pass valve from its seat until the pressure in the discharge port falls below 2000 lbs. The outlet valve 59, similarly to the valve 46, closes and remains closed in the discharge stroke of the pump, and hence the water is allowed to by-pass through the annular chamber 38 into thepassage 32 and through the by-pass 33 into the supply port 34, instead of flowing through the radial ports 56 into the by-pass valve 40. When the pump pressure falls below 2000 lbs. the liftmg force exerted against the trip pin 490 and the opposing weighted arm is accordingly decreased, and therefore the by-pass valve 40 is returned to its seat and the high pressure pump elements start to discharge again until the pressure of 2000 lbs. is reached, thus causing the by-pass valve 40 again to open. The low-pressure bypass valve 39 will remain open until the pressure in the discharge port falls below 100 lbs, whereupon this valve will close and the high and low pressure pump elements will continue in operation until their respective prescribed shut-off pressures are again reached.

It is to be understood that while I have with the small plunger or high pressure an 't.

In some cases the low pressure unitmay be used lndependently of the high pressure unit,

' and vice "ersa.

adapted to be belted with a suitable The preferred driving and 6 adjustable stroke transmitting mechanism hereinbefore I referredto will now be described: The drive shaft 10, which'is driven from any suitablesource of power, is mounted on a large diameter roller bearing 62 and a small diameter roller bearing 63 at the respective sides of the casing 11, which casing at this location is constructed to provide an oil reservoir 64. Said bearings include races 65 mounted in the walls of the casing and held in place by suitable end cover plates and packing caps. The shaft being mounted in this manner after the bearings are assembled, is held in place by a set collar 66. In the present instance the shaft is provided with a large fly wheel 67 motor. The shaft extends through the cross-head 190 to which, in the present instance, the pistons 14 of the respective units are secured, as hereinbefore mentioned. The cross-head comprises an open rectangular structure, including vertical guide walls 68 and connecting side bars 69. Slidably mounted-for independent verticalmovement in the walls 68 of the cross-head is an eccentric bearing structure 70 which is vertically divided into two halves. A vertically-adjustable wedge 71 is preferably interposed between one of the guide walls of the cross-head and the adjacent bearing section so that by vertically-adjusting the wedge the wear between the sllding surfaces may be taken up. To. this end,

; the wedge is provided at its upper end with a perforated lug 72 in which is mounted a vertical adjusting tapped-socket in the top of the adjacent bearing section. Rotatably seated in the eccen- .the

screw 73 that enters a tric opening of the bearing is a relatively large driving eccentric 74 which in its rota- 'ment of the eccentric transversely of the shaft to vary the eccentricity of the eccentric in relation to the axis of the shaft. The driving eccentric is also provided with an elongated cavity 7 7 extending at right angles to length of the slot, which cavity contains an adjusting eccentric 78 which is free to rotate on the drive shaft. This eccentric 78 has formed therein an internal gear 79 that .meshes with a gear 80 also free to rotate on the drive shaft 10, which latter gear, in turn, meshes with a sector gear 81. This sector gear is fast on a stud shaft 82 which is jour- Y naled in the adjacent casing wall and is provided at one side of the casing with-a handle 83 by the manipulation of which the shaft 82 and therewith the sector gear may be swung through a predetermined arc, thus effecting the partial rotation of the gear and perforce moving the internal'gear and correspondingly adjusting the eccentric 78. The handle is provided with a sector extension 84 having therein anv arcuate slot 85 through which extends from the adjacent roller bearmg cover (850) on the casing a screw 86 having a suitable clamping handle 87 by the-manipulation of which the adjusting handle maybe locked in any predetermined position of adjustment.

The adjusting eccentric 78 offsets the center line of the driving eccentric from the center line of the driving shaft at any desired distanceup to-the maximum stroke of the adjusting eccentric, and the sliding connection between the drive shaft and the driving eccentric allows the latter to slide on the shaft to the maximum extent. The adjusting eccentric, although free to rotate on the drive shaft during adjustment, rotates as a'unit with the driving eccentric and the shaft. The adjustable eccentric, with its internal gear, revolves around the gear 80, which is held in place by the adjacent bearing plate 800 and fixed sector gear 81. When the stroke is set at zero the central line of the driving eccentric coincides with the center line of the driving shaft and rotates therewith as a unit, while the cross-head and, perforce, the pumps remain idle, thus saving the wear and tear on the pump parts.

By the construction just described it will be seen that by properly manipulating the handle to adjust the eccentric 78 in relation to the axis of the drive shaft, the stroke of the crosssaid head can be varied fromzero to maximum, while the pump is idle or in motion,and that the eccentric can then be eflectually locked in the desired position of adjustment. This stroke adjusting mechanism is an important feature of my invention and is susceptible of modification and Wide application.

The oil level in the reservoir 64 is such that the driving eccentric 74 in its rotation dips into the oil and carries it to the associated moving parts. The pump casing, which encases the entire pumping mechanism, has drain pockets 88 and drain ports 89 to carry off any leakage of liquid past the packing rings 17 so that the liquid will not escape to the oil reservoir. The casing also has a suitably-disposed removable cover 90 to facilitate inspection of the oilreservoir, and the driving andtransmitting mechanism.

While I have herein, illustrated my invention as embodied in a duplex pump, it is to be understood that the invention may be etubodied in pumps of other types. It is also to be understood that my invention is notlimited to the'form and details of construction herein disclosed as the mechanism may be variously modified within the principle of the invention and the scope of the appended claims.

I claim- 1. In a pump including a main fluid supply port and a suitable discharge, the combination of high and low pressure chambers, hollow pistons simultaneously reciprocable in the respective chambers, the high pressure piston communicating with-the interior of the low pressure piston, a suction valve for the high pressure piston, an inlet and outlet for the low pressure chamber, an outlet for the high pressure chamber, intercommunicating passages connected with the said supply port, one of said passages being communicable with the inlet and outlet of the low pressure chamber and with the discharge, and the other of said passages being communicable with the outlet of the high pressure chamber, and valve elements operable under the influence of pressure in the discharge to control the communication of the respective chambers with the discharge and also with the respective passages leading to the supply port.

In-a pump including a main fluid sup ply port and a suitable discharge, the combination of high and low pressure chambers, hollow pistons simultaneously reciprocable in the respective chambers, the high pressure piston communicating with the interior of the low pressure piston, a suction valve for the high pressure piston, an inlet and outlet for the low pressure chamber, an outlet for the high pressure chamber, intercommunicating passages connected with the said supply port, one of said passages being communicable with the inlet and outlet of the low pressure chamber and with the discharge, and the other of passages being communicable with the outlet of the high pressure chamber, and re-- ciprocable hollow by-pass valves operable under the influence of pressure in the discharge, one of said valves having ports commumcable with the inlet and outlet of the low pressure chamber and with the said discharge and including a lower suction valve and an upper outlet valve adjacent the said valve ports, and the other of said by-pass valves having ports communicable with the outlet of the high pressure chamber and with the said discharge and including an outlet valve for the valve ports adjacent the discharge.

3. In a pump including a main fluid supply port and a suitable discharge, the combination of high and low pressure chambers arranged one within the other, hollow pistons simultaneously reciprocable in the respective chambers, the high pressure piston communi eating at its receiving end with the interior of the low pressure iston, a suction valve at the opposite end of the high pressure piston, a common suction port for the two chambers, said port constituting an outlet port for the low pressure chamber, an outlet port for the high pressure chamber, and operative connections, including by-pass valves, between the ports of said chambers and the said supply port and discharge, said by-pass valves being operable under the influence of pressure in the discharge.

In a pump, pressure-governing means comprising, in combination with the discharge port of the pump, a reciprocable by- 100 pass valve having mlet and outlet ports, a check valve for the outlet port, a valve bonnet, a reciprocable trip pin therein under the influence of pressure in the discharge port, a packing and land for said trip pin, an arm 105 fulcrumed ad acent said bonnet in co-operative relation to the trip pin, and adjustable loading means on said arm. 5. In a pump, pressure-governing means comprising, in combination with the disno charge port of the pump, a reciprocable bypass valve having inlet and outlet ports, a check valve for the outlet port, and packing rings encircling said by-pass valve in the region of the discharge port. and providi-n a 1 chamber in communication with the d ischarge port.

6. A hollow by-pass valve for pumps arranged to be moved in a valve chamber to open connections to cause the pump to idle, 12 there being inlets and outlets to and from the pump, respectively, communicating with the interior of the by-pass valve, and flow control valve means in the by-pass valve controlling said inlets and outlets.

7. A hollow by-pass valve for pumps arranged to be moved in a valve chamber to open connections to cause the pump to idle, there being inlets and outlets to and from I the pump, respectively, communicating with 130 the interior of the by-pass valve,

and a pair of check valves in the by-pass valve for controlling the flow to and from the pump when pumping.

8. A hollow bypass valve for pumps arranged to be moved in a valve chamber to open connections to cause the pump to idle, there being inlets and outlets to and from the pump, respectively, communicating with the interior of the by-pass valve, flow control valve means in the'by-pass valve, means for loading the by-pass valve, and pressure actuated means in communication with the outlet and operable by the discharge pressure to raise the load to permit the bypass valve to move and cause the pump to idle.

9. A pump having an inlet and an outlet, a hollow by-pass valve in a valve chamber between the inlet and outlet, a suction valve and an outlet valve within the by-pass valve, means for loading the by-pass valve, and means actuated by-the pressure at the outlet side of the pump for raising the load on the by-pass valve independently of the valve to permit the valve to move.

10. A hollow by-pass valve for pumps arranged to be moved in a valve chamber to open connections to permit the pump to idle,

there being inlets and outlets communicating with the interior of the by-pass valve, a suction valve in the by-pass valve for preventing flow from the pump tothe inlet to the pump, an outlet valve in the bypass valve for permitting outflow from the pump to the outlet from the pump but; preventing flow from said outlet to the pump, loading means for the by-pass, and a pin extending from the chamber within the by-pass valve to the loading means for raising the load when the pump pressure reaches a predetermined pressure. a K

11. A pump having ,a pressure chamber, a piston in the pressure chamber, means for actuating the piston, a fluid inlet and a fluid outlet for the pump, a by-pass valve chamber communicating with the inlet and outlet, a hollow by-pass valve in the valve chamber, a check valve in the bypass valve for admitting fluid to the pressure chamber and for preventing the flow of fluid from the pressure chamber to the inlet, and pressure actuated means for shifting the by-pass valve to permit fluid to pass, from the pressure chamber to the pump inlet.

12. A pump having a pressure chamber, a piston in the pressure chamber, means for actuating the piston, a fluid inlet and a fluid outlet for the pump, a by-pass valve chamber communicating with the inlet and outlet, a hollow bypass valve in the valve chamber,- acheck valve'in the by-pass valve for admitting fluid to the pressure chamber and for preventing the flow of fluid from the pressure pressure actuated means for shiftm the bypass valve to permit fluid to pass rom the pressure chamber to the pump inlet.

13. A pump having a low and a high pressure chamber, a piston in each chamber, means for actuating said pistons to simultaneously draw fluid into said chambers and to ,expel fluid therefrom, a hollow by-passvalve for the low pressure chamber mounted for movement in a valve chamber, an inlet passage opening into said valve chamber, a passage leading from the said valve chamber to the low pressure chamber, loading means for holding the by-pass valve in a position to cut oflcommunication between the inlet passage and the passage between the valve chamber and the low pressure chamber, an inlet port connecting the interior of the valve with the inlet passage, a port connecting the interior of the valve with the passage to the low pressure chamber, a suction valve for the inlet port, an outlet passage leading from the interior of the by-pass valve, an outlet valve in the by-pass valve for permitting flow from the low pressure chamber to the outlet passage, and means actuated by the pressure in the outlet for unloading the by-pass valve.

14. A pump comprising a casing including a head bolted to one end thereof, a low and high pressure chamber in the casing, a piston in each chamber, means at the other end of the casing for simultaneousy actuating the pistons, a by-pass valve chamber on each side of the longitudinal center of the pressure chambers within the head, a low pressure bypass valve in one of the valve chambers, a high pressure by-pass' valve in the other valve chamber, variable means for loading said valves, an inlet leading to each valve chamber, an outlet leading from each valve chamber, check valves for controlling the flow to and from the pressure chambers, and means actuated by the pressure of'the fluid passing from the respective low and high pressure chambers for unloading the respective bypass valves to permit the respective valves to shift to vby-pass the fluid from the respective pressure chambers to the inlet. I

Signed at Mariners Harbor, in the county of Richmond and State of New York, this 8 June, A. D. 1928.

' 'LLOYD B. GRUMAN.

chamber to the inlet, a second check valve in the by-pass valve for preventing back flow