US2504218A

US2504218A - Pump operating unit

Info

Publication number: US2504218A
Application number: US668942A
Authority: US
Inventors: Paul E Noll; Charles W Crawford; Aller T Dwight; Albert R Rethey
Original assignee: CONS WESTERN STEEL CORP
Current assignee: CONS WESTERN STEEL CORP; CONSOLIDATED WESTERN STEEL Corp
Priority date: 1946-05-10
Filing date: 1946-05-10
Publication date: 1950-04-18
Anticipated expiration: 1967-04-18

Description

April 18, 1950 P. E. NOLL ETAL 2,504,218 PUMP OPERATING UN IT Filed May 10, 1946 7 Sheets-Sheet 1 I ll INVENTORS PAM E. NOLL. CHAELES W 6 9/! WFOID I! I III,

April 18, 1950 P. E. NOLL ETAL 2,504,218

PUMP OPERATING UNIT 7 Sheets-Sheet 2 Filed May 10, 1946 Y 7- DW/Gl/T 144152 ALBEET 2, QFTHEY I 'II/ V L INVENTORS 840A 5 NOLL GI /142155 M. GGAWFOED [Wm/7012.5 Am N011.

P E NOLL ETAL PUMP OPERATING UNIT April 18, 1950 Filed May 10, 1946 April 18, 1950 P. E. NOLL ETAL 2,504,218

PUMP OPERATING UNIT Filed 'May 10, 1946 '7 Sheets-Sheet 4 I N V EN TORS P401 6'. A/OZA P. E. NOLL ET AL PUMP OPERATING UNIT April 18, 1950 7 Sheets-Sheet 5 Filed May 10, 1946 10 B01- END 05 YO. CYL.

PILOT PRESS.

z To 5TOIIAGE 464 TANK 42 W 478 III/LEW];

456 To 801. END F FROM Top 468 can or macn. OF uvu. CYL.

PILOT P1555.

TQSTORAGE A K 42 I N VEN TOR5 PAUL E. NOLL Cfi/AEZES m can men BY Z DWIGA/T Azure Awe-er e. FED/EV April 18, 1950 P. E. NOLL ETAL 2,504,218

PUMP OPERATING UNIT Filed May 10, 1946 '7 Sheets-Sheet 6 Patented Apr. 18, 1950 UNITED STATES PATENT OFFICE PUMP OPERATING UNIT ration of Delaware Application May 10, 1946, Serial No. 668,942

This invention relates to a pump operating unit and has particular reference to a hydraulic power unit which finds particular utility when employed to actuate a reciprocating pump disposed deep within the bore of an oil well.

In the production of petroleum fluids from oil wells which do not flow, it is common practice to employ a reciprocating pump which is located deep within the well bore and which is operated by means of a string of sucker rods extending to the ground surface. The upper or polish rod section of the sucker rod string is ordinarily reciprocated by a pump operating unit consisting of a walking beam, one end of which is connected by a horsehead sling to the polish rod, and the other end of which is connected by a pitman to a rotating crank which is driven by a suitable prime mover, such as an electric motor or internal combustion engine.

Because of the physical limitations imposed by the walking beam construction, the maximum stroke length which may be imparted to the polish rod normally does not exceed six or eight feet, and strokes of about three feet are most common. Since the load on the sucker rod string varies from a maximum during the working stroke to a minimum during the return stroke, the stretching of the sucker rod string may be sufficient in a deep well to reduce the effective pum'p stroke at the bottom of the well bore to only a few inches. A great deal of power, therefore, is lost and the rate of oil production accordingly is very low. Because the motion of a conventional pump operating unit is substantially simple harmonic motion, an attempt to increase the production rate by operating at a higher frequency may give rise to destructive harmonic vibrations in the sucker rod string. Also, the simple harmonic motion employed with the conventional pump operating units provides a return stroke rate which is approximately equal to the power stroke rate, thus consuming considable time with the non-productive portion of the operating cycle.

As is well understood in the art of operating deep well pumps, the sudden reversal of movement at the end of the up stroke and down stroke of the sucker rods imposes reversal strains on the sucker rods as the stretch of the sucker rods is either suddenly released or suddenly imposed upon the rods, and it is, therefore, extremely desirable that the rods not only be brought to rest at the end of each stroke and restarted by a gradual deceleration and acceleration, but there should be a pause or dwell in the movement of 7 Claims. (01. 60-52) v the rods at the end of each stroke, which will permit the strains in the rods to be relieved. The dwell or pause at the end of the down stroke is additionally desirable when the pump is employed to operate a relatively heavy or viscous oil for the purpose of providing a long interval within which the oil may flow into the inlet of the pump to completely fill the pump chamber prior to the initiation of the next up stroke of the pump.

It is, therefore, an object of this invention to provide a pump operating unit which overcomes the above noted disadvantages by employing a hydraulically operated ram which is connected to the sucker rod string.

It is also an object of this invention to provide a pump operating unit of the character set forth in the preceding paragraph, which includes means for adjusting the stroke length up to values greatly exceeding the maximum stroke obtainable with walking beam types of pump operating units.

It is an additional object of this invention to provide a pump operating unit of the character set forth in the preceding paragraphs which includes means for producing a regulatable relatively rapid motion of the sucker rod string during the non-productive portion of the operating cycle.

It is a still further object of this invention to provide a pump operating unit of the character set forth hereinbefore, which includes means for producing a dwell or pause at each end of the stroke.

It is additionally an object of this invention to provide a pump operating unit of the char acter referred to which includes means for adjusting the accelerations and decelerations of the sucker rod string.

It is also an object of. this invention to provide a pump operating unit of the character set forth in the preceding paragraphs which includes a novel hydraulic control valve for obtaining the modes of operation above mentioned.

It is a still further object of this invention to provide a pump operating unit of the character set forth hereinbefore, which includes a novel counterbalancing device, together with means for limiting the velocity of the moving parts in the event of a failure of the sucker rod string.

It is also an object of this invention to provide a pump operating unit of the character referred to in the preceding paragraphs in which the counter-balancing device is of the compressed gas type and which includes means fo automatically maintaining a predetermined average gas pressure.

It is additionally an object of this invention to provide a pump operating unit of the character referred to which includes means for continuously removing entrapped air or gas from the hydraulic system.

Other objects and advantages of this invention will be apparent from a study of the following specifications read in connection with the accompanying drawings, wherein:

Fig. 1 is a side elevational view illustratin the general form and appearance of the preferred embodiment of this invention;

Fig. 2 is a fragmentary cross-sectional View illustrating the details of construction of the hydraulic ram portion of the unit;

Fig. 3 is a diagrammatic side elevational view of the apparatus shown in Fig. 1 and illustrating the piping employed inthe hydraulic power and control-circuits, Fig. 3 illustrating the operation crithedevice during the upstroke of the unit;

Fig; his a cross-sectional view of the main controlcvalve which: is used to control the operation ofxthe' hydraulic ram portion of the unit, Fig. 4 illustrating the positions occupied by the parts of thelvalveduring thephase of operation which iszshownin- Fig; 3;

Fig... 5f ista view: similar to Fig. 3' but showing the apparatus during the down stroke portion of? the [operating cycle Fig: 6; is a. view similar to Fig. 4 but showing. thezp'ositions occupied by the main control valve duringjthadown stroke portion of the operating cycle;

Fig. Iisaview similar to Figs. 3 and 5 but illustraztingia modified formof the invention in which meanssis providedforproducing; a pause or dwell at? each endiof the-operating stroke, Fig. 7 showing. the piping employed in the hydraulic power and controla circuits;

Fig. 8 is a diagrammatic view showing in crossse'ction'the. details of construction of a main controlsvalyeiandianauxiliary control valve employed withzthewmodifiedform of the invention which isi-representedc in Fig.v 7; Fig. 8' illustrating that portion: of" the operating sequence during which the' unitaisa producing a power stroke;

Fig. 9 is a view similar to Fig. 8 but showing theyoperation of the apparatus at the time the ram-:ofrthe:unitapproaches the upper end of the upstroke;

FigaxlDJiS a: view: similar to Figs; 8 and 9 but illustrating the operation of the apparatus during'thewpause-or dwell'which is produced at the top-50f the upstroke;

Fig.- 11. is a view similar to Figs. 8 through 10 but:illustrating the sequence of operation during the return or down stroke of the" hydraulic ram;

Figurez12-iis av iewa similar to Figs. 8 through 11zbuti'illustrating.theoperation at a point near the bottom of thejdown stroke; and

Fig. 1'3'is a view similar to Figs. 8 through 12 but illustrating the positions occupied by the parts during thepause'or dwell which is produced at the bottom of the down stroke.

Referring to the drawings, there is illustrated in Fig. 1 the preferred embodiment of this invention; In accordance therewith, the pump operating unit assembly indicated generally by the reference character I is mounted upon a base frame 2 which may be provided with wheels 3 and 4 and adapted to be raised or lowered into engagement with track membersS-andt to facilitate movement of the unit between an operating position illustrated and a retracted position, giving free working access to a casing head I which is used to terminate the upper end of a well casing 8 and flow tubing 9 mounted concentrically therein, through which a polish rod IEI extends, the polish rod l0 comprising the upper section of a string of sucker rods extended down through the well bore to the reciprocating pump which is mounted at the lower end of the flow tubing.

The unit I comprises a hydraulic ram mechanism indicated generally by the reference character II and comprising an outer cylinder l2 within which is telescopically inserted a ram l3, the ram l3 being movable in a manner to be described hereinafter between a lowermost position such as is illustrated by solid lines in Fig. 1 to an uppermost position such as is illustrated by dotted lines in that figure.

The upper end of the ram I3 is mounted by a head member l4 which servesto journal two pairs of sheaves l5 and I6 A double cable H, anchored as indicated diagrammatically at It by a fixedsheave is passed over the sheaves l5 and I6 and downwardly to a cable attachment I9 by means-of which the ends of the cables I!- are secured to the polish rod II). It will be seen that reciprocal motion of the ram l3'between the solid and dotted line positions illustrated in Fig. 1 will effect a reciprocating motion of the polish rod I0; and that'by reason of the double reeving employed', the stroke imparted to' the polish rod It will be twice the distance through which the ram 13: is reciprocated. By thismeans it is possible toireciprocate the polish rod lfi through a stroke length which greatly exceedsthemaximum stroke length which may be obtained with the conventionalwalkin'g beam type of unit.

The unit I includes-also a housing or enclosure 20; which serves to house the hydraulic equipment: to: be described hereinafter which is used to effects. reciprocation of the ram l3.

As is best shown in Fig. 2, thehydraulic ram construction I l comprises; as stated, the outer cylinder l2 within which the ram I3'is telescopically'mounted. The ram lt preferably comprises a". tubular member, to the upper end of which is attached a head 2| to which is attached, as by means of studs and nuts 22, the sheave supporting head Id. The ram l3'is provided with an overall length substantially equal to or somewhat exceedingthe length of the outer cylinder l2 and i's-madewith a materially smaller diameter than the-inside diameter-of the cylinder l2 to define between the ram and cylinder an annular fluid receiving, space 23. The lower end of the'ram carries an' annular piston member 2% which, by means of sealing rings 25, makes a fluid-tight sliding fitwith' the interior of the cylinder !2. The upper end of the-ram I3- is guided by means ofaguide member 26- which issecured to a-fiange 2'I carried-by the-upper end of the cylinderlz by means-of bolts 28. The upper end'of memberZS forms a stufiing box 28 in which'packing mate rial30'and agland member 31 cooperate toestablish afluid' sealhbetween the ram l3'and the upper end of the cylinder I 2.

The lower end" of the cylinder [2 carries a flange member '33 to which is secured, as by means of bolts 34;a:lower closure member 35. The lower closuremember '35'serves to support a central tubular member 36 which is secured at its lower end to the closure 35' and which is, at its upper end, securedas by means of a flange 31 and bolts 38 to a stationary piston-39 which; by reason of associated sealing rings 40, makes a fluid-tight sliding seal with the inner surface of the tubular ram l3. The tubular conduit 36 serves to deflne within the cylinder |2 a fluid receiving space 4| disposed below the ram piston 24. With the structure thus far described, it will be realized that fluid under pressure injected into the space 4| will cause the ram I3 to rise within the cylinder I2, whereas the injection of fluid under pressure into the annular space 23 above the ram piston 24 will cause the ram l3 to telescopically descend within the outer cylinder |2.

' The manner in which this reciprocating motion of the ram I3 is obtained may be seen by having reference to Fig. 3 wherein the remainder of the equipment and the piping is illustrated in diagrammatic form. As is shown in Fig. 3, there is provided within the housing 26 a storage tank 42 for holding a supply of hydraulic fluid used in the operation of the system. An intake line 43 extends from the storage tank 42 to the inlet of a high pressure positive displacement pump 44, the discharge of which is connected by a conduit 45 to the pressure inlet port of a main control valve 46 which may be described generally as of the four-way type, but it will be described in detail hereinafter.

From the four-Way valve 46 a conduit 41 leads to the annular space 4| beneath the ram piston 24- and another conduit 48 leads to the annular space 23 above the ram piston 24.

Conduits

49 and 59 joining a conduit 5| lead from the fourway valve 46 to the storage reservoir 42.

The piping thus far described provides for the drawing of fluid from the storage tank 42 and supplying that fluid under pressure to the fourway valve 46. Depending upon the operative position of the valve 46, the fluid is supplied either to the cylinder l2 above or below the ram piston 24 to lower or raise the ram piston and the fluid displaced from the opposite side of the piston by the movement thereof is returned to the four-way valve 46 and by means of the conduit 5| to the storage tank 42. As stated, the pump 44 is preferably of the positive displacement type and, therefore, a shunt line 52 is connected between the conduit 45 and the reservoir 42 through a pressure relief valve 53, so that excess fluid transmitted by the pump 44 may be returned directly to the storage tank 42 while a substantially constant operating pressure on the high pressure side of the valve 46 is maintained by the normal operation of the pressure relief valve 53.

The main control valve 46 is hydraulically controlled by means of a four-way pilot valve 54. The valve 54 is connected by a conduit 55 to the conduit 45 through a pressure reducing valve 56. A conduit 51 connects the pilot valve 54 with the storage tank 42 while

conduits

58 and 59 connect the pilot valve 54 with the main control valve 46. In conduit 58 is located a throttling valve 60 which is by-passed by a check valve 6| while a similar arrangement, including a throttling valve 62 and check valve 63, is employed in connection with the conduit 59.

The pilot valve 54 may be of any suitable conventional construction which includes an operating lever 64 so arranged that in one position of the lever 64 the conduit 55 Will be connected to the conduit 59, while the conduit 58 is connected to the conduit 51 and such that in a second position of the lever 64, the conduit 55 will be connected to the conduit 58 and the conduit 59 will be connected to the conduit 51. The operating lever 64 disposed in a position to be engaged by actuating

members

65 and 66 mounted for adjustable movement along a control rod or cable 61 which is preferably attached to the head member l4 to reproduce the reciprocating motion of the ram l3. The

actuating members

65 and 66 are so positioned that the lever 64- is engaged by the actuating member 66 and moved from one position to another as ram 3 nears the upper end of its up stroke, and in such position that the actuating member 65 will engage the operating member 64 and move the valve back to its former position as ram |3 nears the bottom end of its down stroke.

The construction of the main control valve 46 is shown in Fig. 4, in which figure the valve parts are shown as occupying positions corresponding to the phase of operation which is illustrated diagrammatically in Fig. 3, in which the ram 3 has just started its up stroke. As is shown in Fig. 4, the main control valve 46 comprises a body member 68 within which is mounted a cylinder 69. The cylinder 69 is made considerably smaller than the housing 66 to deflne between the cylinder 69 and the housing 68 an annular space 16.

The radial flanges or ribs welded or otherwise suitably secured to the exterior of the cylinder 69 and engaging the inner surface of the housing 68 serve to divide the annular space 19 into a number of chambers including a fluid inlet chamber H to which the conduit 45 is connected as by means of a connecting member 12, a bottom cylinder chamber 13 to which the conduit 41 is connected as by means of a connection 14, a top cylinder chamber 15 to which the conduit 48 is connected as by means of a con nection 16 and fluid return chambers 11 and 18 situated at the ends of the housing member 68 and to which the

conduits

49 and 50 are respectively connected as by means of connection members 19 and 80.

The chamber portions 11 and 18 are communicated with the interior-of the cylinder 69 through the open ends thereof and the chambers 1|, 13 and 15 are communicated with the interior of the cylinder 69 by means of fluid ports extending through the wall thereof.

There is reciprocally mounted within the cylinder 69 a tubular valve spool 8| characterized by

end lands

82 and 83 between which are disposed

intermediate lands

84 and 85. The annular space between

lands

82 and 85 is communicated with the interior of the tubular spool 8| by means of radial ports through the wall thereof as is the annular space between the

lands

83 and 84. a

The ends of the housing 68 are preferably flanged as at 66 and 81 to permit a flanged connection thereto of operating

cylinders

88 and 89. Operating pistons 96 and 9| are slidably mounted within the

cylinders

68 and 89 and are connected to the valve spool 8| as by means of connecting

rods

92 and 93. The outer ends of the

cylinders

88 and 89 are closed respectively by

caps

94 and 95 which include means for attachment of

conduits

96 and 91, the conduit 96 being connected to the downstream side of the

valves

62 and 63 and the conduit 91 being connected to the downstream side of the valves 66 and 6|. It will be appreciated that the admission of fluid under pressure through the conduit 96 to the interior of the cylinder 88 will move the piston thereof downwardly as viewed in Fig. 4 to shift the valve spool.8.| to the positionshown in that figure.

apnea-1s Conversely. the'position oftthe. valvemay bare.- versed by. supplying. fluid under pressure through the; conduit 91'.

In Fig. 3 the-various parts; are. shown in the positions--occupied' at. the beginning of. an up stroke. Near. the end of the down. stroke the actuating member 615. engaged the. operating member. 64. of the valve 54- and moved the; same to.a. position connecting the. conduit. 55: to; the conduit 59. Fluid underpressure from the. pump discharge 45 and through the pressure.- reducing valve 5.6 is thus supplied to, the conduit 59,. and through the check valve63 and conduitilttothe cylinder 88 which was thereby moved to, the positionxshown. in Fig. 4. In that position. hydraulic fluid supplied through the conduit 45 is, com.- municatedto chamber H and through the ports in;:.cyli nder 69 to the annular space aroundvalve .spoolg8ili and between lands e and 8.5, andfrom there. through other ports in the cylinder 69 to thecharnber 13 connecting with the conduit;

Fluidflow is thus established betweenv conduits 45; and 41- to supply fluid, under pressure to the spacefiiwithinthe cylinder I2 beneath; the ram piston 24; Theresulting upward movement of the ram [3 displaces fluid from the annular space 23 which isconveyed through conduit 48 to the chamber and throughthe corresponding cylinder wall-ports; to the annular space between lands 83 and 8.4. From this space the fluid flows through the port inthe wall of the tubular valve spool to the interior of the spool fromjwhere-itg is freeto flowlengthwise into the end chambers I?! and 18. These chambers. are connected to the-conduitsds and 58 so that the fluid displaced from the annularspace 23 within the cylinder 12 is returned through conduit to the storage tank- 42. The ram-i3 continues to rise until the lower. actuating member 66 engages the operatingmember $4 to trip-the pilot valve 54. to its alternate position interconnecting.

conduits

55 and 58. This supplies fluid under pressure through check valve BI and conduit 91'. to the interior of the-cylinder 89, causing; the piston}! therein to move upwardly from. that shown-in Fig; 4, to its alternate positionwhich is illustrated in Fig. 6. In so doing, the fluid contained within the cylinder 88. isdispia'ced'by the accompanying upward movementof the piston 90 and is accordingly returned through conduit 95 and throttling valve 62 to conduit 59 which .is' connected by the valve 54 to. the return line 51leading; to the storage tank 42;

ThlSffiOW of fluidfrom the cylinder 38-- is; all through the valve 62 since the check valve fi3'is opposed to the reverse flow of fluid. Therefore, by adjusting the throttling valve 62, the rate at which fluid is; displaced from the cylinder BB-may be, adjusted so that the valve 46 may be caused to shift .from theposition shown in Fig. 4 to that shownqin' Fig. 6' at a suitably adjusted-relatively slow rate.

As will be seen: from a study of Figs. 4 andzfi andsa comparison of Figs. Sand 5, the shifting of the valve 46. fromthe position shown in Fig. 4 to that shownin Fig. 6 serves to-connect the high pressuresupply represented by conduit 45'to;-the conduit .48 instead of to the conduit. 41, andiserves to connect the conduit 41 to the returnline-fii instead of the conduit 48. This, of course, sup-- plies fluid under pressure to the upperside of the ram-piston to cause the mm to descend... However, sincethe valve spool 81 isslowly movedzbetween the twopositions, the ports traversed by the lands82-85 are gradually closed to uniformly decelerate. the upwardmovement; or the ram (3 and the other ports are graduallyopened to uniformly accelerate the'downward motion. of the ram 53. Since the accelerationand. deceleration isdependententirely upon the rate, of movement orthevalve' spool Bil, it is seen that the throttling valve 62; provides a complete. adjustable controlover. the decelerationand acceleration of theram pistonat the. upper. end of. the ram stroke;

In asimilar way the shifting. of thevalve 46 from the position shown in Fig. 6 to that shown in Fig. 4 occurring near' the end of the: down stroke oftheram, is accompanied by-a return of fluid through the. throttling :valve- 60 which-may. beaadjustedto regulate, asdesired; the deceleration and: acceleration ofthe ram at the. end-of thezdownstroke in thesame wayas has' justbeen described inconnection with the throttling. .valve 62.

Duringthe. above described sequence. of operations the ram.l3 is reciprocated to therebyireciplocate the polish rod 10' through the driving connection. afforded by the cable l'i; It'will bezseen thatduring the up stroke, the'load applied to thecabled i is'the weight of the-sucker rod'string; plus the Weight of the columnof oil lifted; whereas during the down stroke, theweight of the column. of fluid is carriedby the-foot valve of-the oil wellpump so that there is'applied to the-cable l 'i'zonly-thaweight of the sucker rod string. Accordingly, to avoid an undesirable condition-of varying loadzon the prime mover, it-is' preferred to apply an upward acting counterbalancingforce to balancmthe weight'of the sucker rod string, plus approximately one-halrof the weight of the columniof fluid contained within the flow tubing,

This-.counterbalancing force is preferably appliedto the interior of the ram. I3'by means-of an incompressible fluid suchas oil whichfills aspace 98.='comprising;theinterior of the tubular ram [3 and which communicates with the interior of the centralxtuhular. member 36; as is best shown in Figs. .,2$'and.=3.- The tubular member-.36 is'connectedz'to a. c0nduit 99; by means .of a flanged attachment-IEO which is secured as by means of bolts all]! tuthe-lower closure member 35'. The conduit-39.15 connected, as shown in Fig. 3; to-the interior. of an; annular pressure chamber- I02 which,pby preference, surroundsthe outer cylinder l2;and is secured theretoas by means of welding [63.1. The :pressure chamber'lM is partially filled withrincompressible fluidwhile. the upper portion is filled with gas under pressure. The'gas con.- tained within the upper portion of the chamber [0211s iintroduced'at apressure suflicient tocause the incompressible fluid conducted torthe interior of." the rams-i3 through the conduits 99and-36-=to exert an upward force onthe ram l3 equal-tothe desired counterbalancing force to be exerted.

In;orde'r .to compensate :forthe possible loss. of gasfrom the upper portion of the pressurecham bera IE2; thereis provided a make-up pumpindi catedgenerallyatifldin Fig. 3.: TheJpump I04 preferablycomprises a cylinder'member- I05 which is :bored'as at N16 to receive a pistoniifll. To thepiston Hi! there is secured apistonex-tension I08 whichisaadaptedi to reciprocate within a gas compressing. bore I09; Ansintake line-l I0. is adapted to be connected to .asuitable source of gasor in the event air islused as the gas to fillthe pressure chamber 102,. the endofztheconduit I I0 is merely eommunicatedqwith the atmosphere.

Thai conduit H9 communicates through a check valve 1 i iwto the interior of the gas com.- pressi'ngccylinder; bore-ml 09.: Aadischarge-pline. It:

also communicates with the interior of the bore I09 and is passed through a check valve H3. Fromthe check valve II 3 a conduit H4 leads to the interior of the pressure chamber I02, as shown at H5. With the construction thus far described, it will be seen that reciprocation of the piston extension I08 will draw gas into the bore I09 during the down stroke of the piston and will during the up stroke thereof deliver said gas under pressure to the interior of the pressure chamber I02.

The piston extension I08 is reciprocated by the application of fluid pressure alternately to opposite ends of the cylinder I06. For this purpose conduits II 6 and II I afe connected between the bottom of the cylinder I06 and the line 41 which leads from the valve 46 to the lower end of the main hydraulic ram cylinder. Similarly, conduits H8 and H9 lead from the upper end of the cylinder I06 to the line 40 connecting the main control valve 40 with the upper end of the main hydraulic cylinder. Since fluid under pressure is alternately supplied to and returned from each of the lines 4! and 48 by the action of the main control valve 46, it will be seen that the piston I! and piston extension I 08 will be reciprocated in synchronism with the reciprocation of the ram I3 and that as a result thereof, air or other suitable gas will be continually forced into the pressure chamber I02.

In order that the pressure within the chamber I92 may be held at a proper and regulated value, a manually adjustable pressure relief valve I20 is connected to the interior of the chamber I02 as by means of a conduit I2I. In normal op,- eration, the gas make-up pump I04 supplies gas at a rate in excess of the leakage requirements so that the excess may be discharged through the pressure relief Valve I20. This valve then operates to maintain a substantially constant average pressure within the interior of the pressure chamber I02. I d

In the event the sucker rod string should break, the load which is applied to the ram I3 would be instantly materially reduced, with the result that in the absence of some means for arresting or retarding upward movement of the ram, the counterbalancing force exerted by the gas compressed within the pressure chamber I02 would cause the ram I3 to rise at a destructive velocity.

Accordingly, the present invention includes a velocity limiting valve I22 (see Fig. 2) which comprises a disc-like valve member I23 mounted upon a stem I24 which is slidably mounted in a guide I25 carried by a spider I29 secured to the conduit 99. A spring I2! is employed .to normally urge the valve I23 to a retracted position, such as that shown in Fig. 2, in which the valve member I23 is spaced from a seat I20 which it is adapted to engage in its upper position. A plurality of apertures or ports I29 are provided in the valve disc I23 so that in its upper position, the flow of fluid through the

conduits

99 and 36 will not be completely arrested but merely throttled.

The pressure of the spring I2! is so adjusted as to maintain the valve I23 in the normal position shown in Fig. 2 during normal operation of the apparatus. However, should the sucker rod string break or the downward load imposed upon the ram I3 be for any other reason immediately relieved, then flow of fluid through the conduit 99 and past the valve I 23 will rise to a value mate- 10 rially exceeding the normal rate of flow. The hydraulic friction drag exerted on the valve I23 will then overcome the force of the spring I 21 and move the valve I23 to its closed position so that thereafter fluid transferred from the conduit 99 to the conduit 33 must be passed through the small holes I29 in the valve disc I23. This throttling action serves to limit to a, safe value the rate of upward movement of the ram I3.

In order for the above-described counterbalancing action to take place continuously and over long periods of operation, it is necessary that any gas which may move into the space 98 be removed therefrom to prevent an accumulation of gas in the upper end of the interior of the ram I3. To this end there is provided a scavenging pump indicated generally by the reference character I30 which comprises a cylinder member I3I' mounted upon a lower head member I32 which is in turn carried by uprights I33 secured to the stationary piston 39. A piston I34 is reciprocally mounted within the cylinder I3I and carries a tubular piston rod I35 which extends through an intake check valve I36 to an inlet conduit I31 which is terminated in a position to be engaged by an upper cap member I38 (serving as a closure for the interior of the ram I3) during the last few inches of downward travel of the ram I3. This serves to move the piston I34 downwardly within the cylinder I3I. When the ram I3 is moved upwardly, the piston I34 is simultaneously moved upwardly by means of a compression spring I39 which surrounds the cylinder I3I and is engaged between the lower head I32 and a disc-like member I 40 secured to the piston rod I35. The head member I32 is chambered as shown in Fig. 2 to house a dis charge check valve I4I which communicates with a conduit I42 which is connected as shown in Fig. 3 to an external conduit I43 connecting with the conduit I I5.

It will be seen that the structure just described comprises a small pump mounted within the interior of the ram I3 and which operates to take in fluid or gas from the extreme upper end of the space 98 and discharge the same through the conduits I 42 and M3 to the conduit H5 by which it is returned to the interior of the pressure chamber I02. Thus, any tendency for gas or air to collect in the space 98 is completely offset by the removal of that gas as fast as it accumulates.

As hereinbefore stated, it is desirable to provide in a control system of the character de scribed a means for causing the ram to pause for a predetermined length of time at each end of the stroke. There is accordingly illustrated in Figs. 7 through 13 an alternative-embodiment of the present invention which includes the necessary control apparatus for providing such a pause or dwell at each end of the operating stroke. As will be apparent from Fig. 7, the apparatus employed is substantially identical to that which has been described hereinbefore except for the substitution in place of the valve 46 of a different main control valve Which is indicated generally in Fig. 7 by the reference character I 44 and the association therewith of a dwell cylinder I 35. Also, there is interposed between the conduit 35 leading from the pump 43 and the pressure inlet port of the four-way control valve I44 a resistance valve I89, the purpose of which will be described hereinafter.

As before, the main hydraulic power supply connections comprise

conduits

47 and 48 leading from; the four-way control valve 44 respectively to the lower and upper ends of the hydraulic cylinder I2 andreturn lines 45, 55 and BI leading from the four-way control valve I44 to the reservoir 42. As in the previously described modification, the pilot control valve 54 is connected by the conduit 55 and pressure regulating valve 56- to the conduit 45 and is provided with the return line 51 leading to the reservoir 42. Inthealternate positions of the pilot control valve 54, it is adapted, as before, to connect the conduit '5- to

conduits

58 and 59, which conduits lead to the maincontrol valve I44 and the associated apparatus to be described hereinafter. The valve 54 is shifted between its two operating positions by means of the operating member 61 and the val-vepontrol lever 54.

In Fig. 8 there is illustrated the construction of; the four-way control valve I44 and the constructionof the dwell cylinder I45. There is also showndiagrammatically the piping which interconnectsthese two valves with the pilot con-trolvalve 54. The main control valve I44 is substantially identical to the control valve 44 hereinbefore described, the principal difference residing inthe construction of the valve spool MA and the operating cylinders 851 39 and the

pistons

95, 94 therefor. Y

Aswill be seenin Fig. 8-, at one end of each of the cylinders 88 and 89' there are mounted sliding sleeves I46 and I4! which make sealing engagements piston-Wise with the Walls of the

cylinders

88 and 89 and which in turn slidably receives the inner end of the pistons Bil, 9L Mechanical connection between the sleeves 45 and M1 and the associated pistons is effected by means of annular members I48 which are securedto theouter ends of the sleeves I46 and I4'I- and which flange inwardly behind the enlarged end of the spool pistons: which are received within the sleeves. By inspection of Fig. 8', it will be seen that an inward movement of either sleeve I46 or I4'I- will mechanically drag the pistons 90 or 9| therewith to a midposition,

but that the pistons are each permitted additional inward movement to an extreme inner position'.- It will also be seen that upon move mentof either piston to its extreme outer position as, for example, that occupied by the piston- 90 in Fig. 8, the corresponding sleeve will be mechanically moved to its outermost position.

In Fig. 8 the parts are shown inthe position they occupy during an upward stroke of the ram I3. It will be seen that fluid under pressure supplied to the conduit 45 is conveyed to the conduit 41 through the valve I44 and to the lower end of the hydraulic cylinder I2. Fluid returned from the upper end of the hydraulic cylinder I2 is returned through conduit 48 through the valve I44 to conduits 49 and 59' and from there to the conduit 51 and storage tank 42.

During this time pilot control pressure derived from the conduit 55 is conveyed through the control valve 54 and conduit 58 to a conduit I49 communicatingwith the interior of the cylinder 89. In this part of the cycle of operations the piston 9| and sleeve I41 associated therewith occupy the position shown in Fig. 8 so that fluid may flow from conduit I49 through the interior of the cylinder 9I to a conduit I50 which is connected through a check valve I5I to the righthand end of the dwell cylinder I45 which comprises an elongated hydraulic cylinder I52 with 12 in which is reciprocally mounted a spool-shaped piston member I53.

The piston member I53 now occupies the e'x-- treme left-hand position, in which position the right-hand end of the spool I53 lies between a centrally located inlet conduit I54 and a conduit connection I55. Therefore, in the position shown, fluid flowing. into the interior of the cylinder I52 through the check valve I5I may flow out the conduit I55 and through a check valve I58 to a conduit I5'I which communicates with the righthand end of the cylinder 89 to' thereby urge the piston 9'I to the left to the position shown in Fig. 8.

As the ram I3 approaches the upper end of the up stroke, the valve 54 is shifted to its alternate position to supply control pressure from the source conduit 55 to the conduit 59 and at the same time to release pressure from conduit 53 through conduit 51 to the storage tank. As is shown in Fig. 9, the supply control pressureis conveyed through a conduit I58 to the interior of the cylinder 88 ata point to the left of sleeve I46, as viewed in Fig. 9. This pressure is effective to cause the sleeve l46' and piston to move to the right as viewed in Fig. 9 because the area of the end of the sleeve I45 is greater than the area of the left-hand end of the piston 90. The resulting movement of the piston 90 to the right moves the main control valve I44 toward a neutral position. As this motion takes place, fluid to fill the left-hand end of the cylinder 88' is drawn through conduits I59 and I69, check valve I6I and con'duit I62 communicating with the interior of the dwell cylinder I52. Because of the then position of the dwell piston I53, the conduit I62 is communicated with the inlet conduit I54 so that fluid may be drawn in through that conduit through a check valve I53 and a conduit I64 which is in communication with the storage tank 42. Likewise; fluid displaced from the interior of the cylinder 89 by movement of the piston 9| to the right is discharged through the conduit I51. It is preventedfrom flowing into the conduit I55 by reason of the check valve I56 and is, therefore, forced to flow through a conduit I55, throttling valve I66 and check valve I61 to the conduit 58 which is connected through the control valve 54 to the conduit 51 which returns to the storage tank 42'.

The described movement of the piston 93 to the right continues until the spool BIA of main control valve I44 reaches a neutral position, at which time the sleeve I46 associated with the piston 90 has seated against stop I-46A and has uncovered a port leading to a conduit I68 which directs the pressure fluid through check valve I69 and. conduit I'IIl to the left-hand end of dwell cylinder I52.

As is shown in Fig. 10,- the neutral position of the spool 8IA in main valve I44 is such that the pressure supply line 45 is communicated directly with the two

return lines

49 and 54 while the two

cylinder lines

41 and 48 are closed off. In this position of the valve, therefore, movement of the ram I3 is arrested and the ram remains stationary so long as the spool 8IA remains in the neutral position.

The rate of movement of the main valve from the position shown in Fig. 9 to that shown in Fig. 10 is controlled for the purpose of controlling the rate of deceleration of the ram I3 by adjustment of the valve I56 which regulates the rate at which fluid may be displaced from the cylinder 89 by the movement of the piston 9| therein. When the valve I44 reaches a neutral position as shown in Fig. 10, the uncovering of the port leading to the conduit I68 intercommunicates the conduits I58 and I 68 so that fluid under pressure delivered from the control valve 54 through conduit 59 may flow through the conduit I68, a check valve I69 and conduit I10 to the left-hand end of the dwell cylinder I 52. The pressure thus applied to the left-hand end of the piston I53 causes said piston to move to the right within the cylinder 152 toward the opposite end of the cylinder.

During the first part of this motion the righthand end of the piston I53 closes the port leading to the conduit I55 so that fluid contained within the cylinder I52 to the right of the piston I53 will be displaced therefrom through conduit I'II, throttling valve I12 and conduit I59 to the interior of the cylinder 89. By virtue of the sliding interconnection of the piston 9I with the sleeve I41, the movement of the piston 9| to the right to the midposition did not produce any motion of the sleeve I41 so that a fluid connection between conduits I50 and I49 remains through the interior of the cylinder 89. Fluid thus passed-into the conduit I49 is conveyed by conduit 58 to the control valve 54 and thence by way of conduit 51 to the storage tank 42.

The flow of the displaced fluid just described is forced through the throttling valve I12 by reason of the flow being in a direction reverse to that permitted by the check valve II. Thus adjustment of the throttling valve I12 may be employed to control the rate of travel of the piston I 53 within the cylinder I52 and, therefore, the length of time required for the piston to move from the position shown in Fig. to that shown in Fig. 11. When the piston I53 finally reaches the right-hand end of the cylinder I52 as is shown in Fig. 11, the left-hand end of the piston. I53 uncovers the port which communicates with the conduit I62. This establishes a communication between the conduits I10 and I62 so that fluid flowing into the cylinder I 52 through the conduit I10 may now flow through conduit I62, check valve I6I and conduits I60 and I59 to the interior of the cylinder 98 at the left-hand end of the piston 90. This application of pressure to the left-hand end of the piston 90 causes the piston to move to the right to shift the spool 8IA of main control valve I44 to its other operating position in which fluid under pressure supplied through conduit 45 is conveyed to the upper end of the hydraulic cylinder through conduit 48 while fluid returned from the lower end of the hydraulic cylinder through conduit 41 is conveyed by means of

conduits

49, 50 and 5| to the storage tank 42, thus starting the descent of the ram on its down stroke. During movement of the valve spool BIA from th position shown in Fig. 10 to that shown in Fig. 11, fluid is again displaced from the cylinder 89 through conduits I51, I65 and valves I66 and I61 as was described in connection with Fig. 9. As before, the valve I56 in throttling this flow regulates the rate of travel of the valve spool BIA to the position shown in Fig. 11.

The valves remain in the position shown in Fig. 11 until the ram I3 approaches the lower limit of its down stroke, at which time the pilot control valve 54 is tripped to its first position connecting the pressure source line 55 to the conduit 58 and connecting the conduit 59v to the re-- turn line 51 leading to the storage tank 42 as shown in Fig. 12. In this position fluid under pressure is conveyed through conduits 50 and I59 to the interior of the cylinder 89 to act on the sleeve I41 and move that sleeve and the piston 9I to the left, as viewed in Fig. 12, to move the spool BIA of main control valve I44 from a position shown in Fig. 12 to a neutral position, such as is shown in Fig. 13, in which

position conduits

41 and 48 leading to the hydraulic cylinder are cut oif and flow is established between the pressure supply conduit and the

return conduits

49 and 50.

During movement of the spool 8IA of main valve I44 to the left, fluid displaced from the cylinder 88 by movement of the piston 90 therein as conveyed through conduit I 59, conduit I13, throttling valve I14 and check valve I15 to conduit 59 which is connected through the control valve 54 to the return conduit 51 leading to the storage tank 42. Flow of fluid from the conduit I59 through conduit I60 is prevented by the check valve I6 I. The rate of movement of the spool 8 IA to the left is controlled by regulation of the throttling valve I14.

When the main valve reaches a neutral position as is shown in Fig. 13 communication is established between conduits I49 and I to supply fluid under pressure through check valve I5I to the right-hand end of the dwell cylinder I52 to cause the piston I53 thereof to move to the left from the position shown in Fig. 13 to that shown in Fig. 8. During this movement fluid which is displaced by the movement of the piston I53 from the left-hand end of the cylinder I52 is conveyed through conduits I10, I15, throttling valve I11, conduit I18, conduit I68 through the cylinder 83 and by way of conduits I58, 59 and control valve 54 through conduit 51 to the storage tank 42. The check valve I69 forces the fluid to flow through the throttling valve I11, which may be used to regulate the rate of travel of the piston I53 to the left within the cylinder I52 and, therefore, determine the length of time the ram I3 remains stationary at its lowermost position. When finally the piston I53 reaches the extreme left-hand position in moving from the position shown in Fig. 13 to that shown in Fig. 8 communication is established as shown in Fig. 8 between conduits I50 and I55 so'that fluid may flow through check valve I55 and conduit I51 to the right-hand end of the cylinder 89 and cause movement of the main valve I44 to the left to the position shown in Fig. 8, in which position hydraulic fluid is supplied to the main cylinder I2 in such a manner as to cause the ram I3 to rise therein.

As before, fluid displaced by movement of the piston 90 will be returned through conduits I59 and I13 and through the throttling valve I14 so that the rate of movement of the main valve is subject to control to thereby regulate the acceleration of the ram in the upward direction. As the ram nears, the upper limit of its upward stroke, the above-described cycle of operation is repeated.

Reference has been made hereinbefore to the resistance valve I80. This valve is connected, as shown in Fig. '1, and arranged to be operated by a control connection I19, by means of which pressure existing in the pressure supply line ahead of main valve I44 is applied to overcome a spring in valve I60 and hold the valve open. It will be seen that during the neutral position of the main valve 444, as is shown in Figs. 10 and 13, the hydraulic power fluid supplied to the valve I44 is returned directly to the storage tank 42 against little, if any, resistance. When this occurs, the sprin in valve I partially closes the valve to maintain within the conduit 45 a pressure suificient to supamnesia Ihis pump operating unitisparticularly ad pted for tbisrt pe b op a by virtue -of the construction of the'double acting hydraulic ram-described herein.

It :will be observed that-the piston 24- has, aconsidera l s ea e a a expo d t t e'fl ds at its -.lowcr end :than at upper (end and thus, the rump 44 ;is;; reguired to deliver -a, considerably .;gre.a,ter quantity of iiuijd during the upstroke of the :51. than is-requireditobedelivered during .thedown stroke. :By reason of this :construction, the operation of the pump 44 asa-constantvolume delivery pump will automaticallyproduce a much mQ e-raPidd Wn St 1P t k of the 311311! and cpnsequentlyasimilar difference-in rthespeed of 'movement of the sucker rods.

53y reierring pa rticularlyto Fig. 5, :it will be observed :that during --the; down stroke of=1the ram .pistonglkthepump t4 delivers fluid through the conduit t xti e spa e 23 and i will l o be observedrthatthe eonduit --l 118- which connects with the :conduit ,48 is coupledzto the tank t2 witha valve 2-00 interposed in=the conduit H8. Hence, therate of speed onthe downstroke may beregulated ;b controlling valve 200. If va1ve 200 is -opened sli h ly, a portion of the fluid delivered by the pump will Joy-pass through the conduit 4 [8 back to the tank A4, while the remainder of the fluid delivered by thep mp .44 .Will be delivered to the annular-space 23. Hence, asthe valve 200 is moved to progressivelygreater open positions t e O lme o flui uch Wil ad i e d to the annular space 23 will be progressively diminished and the down stroke of the ram ,will be progressively slower and. slower.

From the foregoing, it will be observed that the above-described invention comprises apump operating-unit superior in many ways to pumping of conventional iorm. .Attentionis directed particularly to the employmentof ,a double-acting hydraulic ram asthe means for applyingre- ,ei procatipg pow-er tothe sucker rod string and to the control mechanism which has been described hereinbefore for controlling the operationof the rain.

Attention is directed particularly to the provision of the throttling valves for adjusting the acceleration rates at each endof th stroke, and it is tO be particularly noted that with the apparatus as described hfilein, the acceleration rate ;.at the upper endof the stroke may be adjusted independently of the adjustment of the accelera- ,tionrate-at the bottom end of thestroke.

It will be noted that there has also been provided a control mechanism for causing theram =toremain stationary for a predetermined len th of time at bothends of the stroke and that provision .has been made .ior separately and independently adjusting theduration of the inactive periods.

The provision .of the gas pressure counterbalancing system, together with the automatic safety, scavenging and makeeup devices therefor permitsubstantial savings in the power required to produce oil from a given well at agiven rate.

While t er has been shown and des r d e preferred embodiment .of the present invention,

the same isnotto be limitedto any-of 'the details of construction-shown or described hereirn except ,as defined in the appended claims.

What is claimed as new is:

l. Inapumping unit, the combination of: a double-acting hydraulic ram including a ram member reciprocal in a cylinden'a source of fluid under pressure, and. a valve movable between two alternate positions connecting said source respectively to opposite'ends of said cylinder to reciprocate said ram member througha predetermined stroke; hydraulic means operable to move said valve between said alternate positions;

control means coupled to said hydraulic means and responsive to ,arrival f said ram member at points nearthe ends of said stroke for operating said hydraulic means; and -means cooperating with said hydraulic means for arresting movement of said valve .for a-predetermined time substantially midway between-said-alternate positions to thereby hold said rammember, stationary for saidpredeterminedtime at the ends of said stroke.

2. Ina pumping unitior reciprocating .a sucker rod string extended to a reciprocating pump located in a well bore, the combination-of a doubleacting hydraulic ram comprising an .outer cylinder, a piston reciprocal in,said cylinder, a tubular ram member secured to said piston and ,defining an inner cylinder, a stationaryv piston fitted into said inner cylinder, and means for supplying hydraulic fluid under ,pressurealternately to 0p- ;posite ends of said outer cylinder and to one end of said inner cylinder .to meciprocate said ram member; .'means connecting said ram member .to said sucker rod string-to reciprocate said string inresponse toreciprocationof saidram member; a pressure chamber containing an expansible fluid under pressure; and a tube extending through said stationary piston for connecting said pressure chamber to the other end of said inner cylinder to. thereby oppose the force exerted by said sucker rod strin on said ram member.

3. In a pumpingunit for reciprocating a sucker rod string extended to a reciprocating pump located in a Well bore, the combination of :.a double- .acting hydraulic ram comprising an outer cylinder, a piston reciprocal in said cylinder, a'tubular ram member secured to said piston and defining an inner cylinder, a stationary piston fitted into said inner cylinder, and means for supplying hydraulic fluid under pressure alternately to opposite ends of said outer cylinder and to one end of said inner cylinder to reciprocate said ram member; means connectin said ram member to said sucker rod string-to reciprocate said string in response to reciprocation of said ram member; an annular pressure chamber surrounding said outer cylinder and containin an expansible fluid under pressure; and a tube extendin through said stationary piston for connectingsaid pressure chamber to the other end of said inner cylinder to thereby oppose the force exerted by said sucker rodstring onsaid ram member.

4. In a, pumping unit forreciprocating a sucker rod string extended to a reciprocating pump located in a well bore, thecombination of: a'doubleacting hydraulic ram comprising an outer cylinder, apiston reciprocal in said cylinder, a tubular ram member secured to said piston and defining-an inner cylinder, a stationary piston fitted into said inner cylinder, and means for supplying hydrauli fluid under pressure alternately to opposite ends of said outer .cylinder and to one end of said inner cylinder to reciprocate said ram member; means connecting said ram member to said sucker rod string to reciprocate said string in response to reciprocation of said ram member; a Pressure chamber containing an expansible fluid under pressure; conduit means extending through said stationary piston for connecting said pressure chamber to the other end of said inner cylinder to thereby oppose the force exerted by said sucker rod strin on said ram member; and a flow responsive valve in said conduit for partially closing off said conduit when the rate of flow therethrough reaches a predetermined maximum rate.

5. In a pumping unit for reciprocating a sucker rod string extended to a reciprocating pump located in a well bore, the combination of a doubleacting hydraulic ram comprising an outer cylinder, a piston reciprocal in said cylinder, a tubular ram member secured to said piston and defining an inner cylinder, a stationary piston fitted into said inner cylinder, and means for supplying hydraulic fluid under pressure alternately to opposite ends of said outer cylinder and to one end of said inner cylinder to reciprocate said ram member; means connecting said ram member to said sucker rod string to reciprocate said string in response to reciprocation of said ram member; a pressure chamber containing an expansible fluid under pressure; conduit means extending through said stationary piston for connecting said pressure chamber to the other end of said inner cylinder to thereby oppose the force exerted by said sucker rod string on said ram member; a valve member in said conduit movable from a normally open position to a position partially closing off said conduit, said motion being in the same direction as the flow of fluid therepast during an upward motion of said sucker rod string; and spring means normally urging said valve toward said normally open position.

6. In a pumping unit for reciprocating a sucker rod string extended to a reciprocating pump located in a well :bore, the combination of: a doubleacting hydraulic ram comprising an outer cyllnder, a piston reciprocal in said cylinder, a tubular ram member secured to said piston and defining an inner cylinder, a stationary piston fitted into said inner cylinder, and means for supplying hydraulic fluid under pressure alternately to opposite ends of said outer cylinder and to one end of said inner cylinder to reciprocate said ram member; means connecting said ram member to said sucker rod string to reciprocate said string in response to reciprocation of said ram member; a pressure chamber containing an expansible fluid under pressure and a heavier incompressible fluid; a tube extending through said stationary piston for connecting the bottom of said pressure chamber to the other end of said inner cylinder to thereby transmit through said incompressible fluid the pressure exerted by said expansible fluid and apply to said ram member a force opposing the force exerted thereon by said sucker rod string; a pump in the upper end of said inner cylinder operable to pump fluid from the extreme upper end of said inner cylinder to the upper portion of said pressure chamher; and means responsive to reciprocation of said ram member for operating said pump.

7. In a pumping unit for reciprocating a sucker rod string extended to a reciprocating pump 10- cated-in a well bore, the combination of: a doubleacting hydraulic ram comprising an outer cylinder, a piston reciprocal in said cylinder, a tubular ram member secured to said piston and defining an inner cylinder, a stationary piston fitted into said inner cylinder, and means for supplying hydraulic fluid under pressure alternately to opposite ends of said outer cylinder and to one end of said inner cylinder to reciprocate said ram member; means connecting said ram memher to said sucker rod string to reciprocate said string in response to reciprocation of said ram member; a pressure chamber containing an expansible fluid under pressure; a tube extending through said stationary piston for connecting said pressure chamber to the other end of said inner cylinder to thereby oppose the force exerted by said sucker rod string on said ram member; pump means operable simultaneously with the reciprocation of said ram member to pump expansible fluid into said pressure chamber; and a pressure relief valve on said pressure chamber for limitin the pressure of fluid therein to a predetermined maximum value.

PAUL E. NOLL.

CHARLES W. CRAWFORD. T. DWIGHT ALLER. ALBERT R. RETHEY.

REFERENCE S CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,223,741 Schwister Apr. 24, 1917 1,619,474 Hubbard Mar. 1, 1927 1,906,965 Hobson May 2, 1933 1,978,346 Ernst et al. Oct. 23, 1934 2,072,595 Hutchison Mar. 2, 1937 2,151,057 Suth Mar. 21, 1939 2,157,219 Salentine May 9, 1939 2,167,623 Britter Aug. 1, 1939 2,253,617 Grifiith Aug. 26, 1941 2,276,358 Vickers Mar. 17, 1942 2,277,761 Hubbard Mar. 31, 1942 2,282,977 Mast May 12, 1942 2,304,131 Vickers Dec. 8, 1942 2,357,986 Wichterman Sept. 12, 1944 2,390,124 Ross Dec. 4, 1945