US2934899A

US2934899A - Oil well pump drive unit

Info

Publication number: US2934899A
Application number: US468118A
Authority: US
Inventors: Koplin Harry; Sr Arthur R Slate
Original assignee: ZEPHYR LAUNDRY MACHINERY COMPA
Current assignee: ZEPHYR LAUNDRY MACHINERY Co; ZEPHYR LAUNDRY MACHINERY COMPA
Priority date: 1954-11-10
Filing date: 1954-11-10
Publication date: 1960-05-03
Anticipated expiration: 1977-05-03

Description

May 3, 1960 Filed Nov. 10. 1954 H. KOPLIN ET AL OIL WELL PUMP DRIVE UNIT 5 Sheets-Sheet l May 3, 1960 H. KoPLlN ET AL 2,934,899

OIL WELL PUMP DRIVE UNIT Filed Nov. l0, 1954 5 Sheets-Sheet 2 H AKKY KOP-U N May 3, 1960 H. KOPLIN ET AL l 2,934,899

OIL WELL PUMP DRIVE UNIT INVENTORS AKTHUK KELATE, 5K

HARRY KOF-'LIN w M wf @w ATTORNEYS A H. KOPLIN ET AL OIL WELL PUMP DRIVE UNIT 9 May 3, 1960 Filed NOV. 10, 1954 5 Sheets-Sheet 4 HARRY KOPLIM by @l/Uf [Zl/#ATTORNEYS ay 3, 1960 H. KOPLIN ET AL 2,934,899

OIL WELL PUMP DRIVE UNIT Filed Nov. l0, 1954 5 Sheets-Sheet 5 my? uw INVENTOR5 ARTHUR K SLATEzSR.

ARR KOPLlM H Y mi if@ EDY ATTORNEYS United OIL WELL PUMP DRIVE UNIT Harry Koplin, Glencoe, and Arthur R. Slate, Sr., Chicago,

Ill., assignors to Zephyr Laundry Machinery Company, Chicago, lll., a corporation of Delaware Application November 10, 1954, Serial No. 468,118

z claims. (ci. so-sz) This invention relates to improvements in pumps and more particularly relates to an improved hydraulically v operated drive unit for reciprocably driving oil well PUIIIPS- A principal object of the invention is to provide a simplied and improved form of hydraulic drive mechanism particularly adapted for 4oil well pumps and 'arranged with a view towardutmost simplicity and eiciency in construction and operation.V

Another object of the invention is to provide a hydraulically operated oil well pump drive unit including a vertical hydraulic operating cylinder which may readily be set in place, and in which the hydraulic operating cylinder for the pump and support therefor may readily be moved back and forth along a supporting base therefor, Vto enable the well to be pulled without disconnecting the pump or cylinder from the drive mechanism and supply lines for supplying fluid under pressure thereto.

A further object of the invention is to provide a novel and eicient iiuid system particularly adapted for driving oil well pumps by hydraulic power and so arranged as to enable accurate control as to reciprocable movement of the drive piston for the pump to be attained.

Still another object of my invention is to provide a hydraulically operated cylinder and piston for driving an oil well pump in which a novel form of control means is provided to control downward movement of the hydraulic piston at the lower portion of its stroke, to eliminate shock to the piston and the well rods driven thereby.

Another and important object of our invention is to provide a hydraulic system for reciprocably driving a uid pressure cylinder and piston connected to reciprocably drive the well rods, piston and valve of an oil well pump, so arranged as to aiford a more accurate control of reciprocating movement ofthe drive piston, and to so arrange the fluid system as to avoid excessive heating of the hydraulic fluid and over-taxing the hydraulic pump providing fluid pressure to the system.

Still another object of the invention is to provide a novel and improved hydraulic operating system for oil well pumps and the like in which the hydraulic system and circuit to the pump drive motor is so arranged as to prevent stopping of the piston and pump reciprocated thereby, until it has made a complete upstrokeV and has started on its down-stroke.

These andother objects of our invention will appear from time to time as the following yspecification proceeds and with reference to the accompanying.v drawings wherem.

pump, with certain parts thereof removed and broken away; v

Figure 3 is a' horizontal sectional view taken substantially alongthe line 3-3 of Figure 2;

iFigure 4 is a view of-the pump drive lmechanism some- Figure 1 is a view in side elevation of ar hydraulic drive` 2,934,899 Patented May 3, 1960 what similar to Figure 1, but looking at the drive unit from the opposite side thereof from Figure l, and showing the drive unit in retracted relation with respect to its support frame structure.

Figure 5 is a detail view showing the operating mechanism for operating the pilot valve, controlling up and down movement of the piston of the drive unit; and

Figure 6 is a fluid diagram illustrating the hydraulic system for the drive unit and also diagrammatically illustrating the control circuit to the motor for driving the hydraulic pump to provide iiuid under pressure for the drive unit.

In the embodiment of our invention illustrated in the drawings, we have shown in Figures l, 2, 3 and 4 a base frame structure 10 adapted to be mounted on a suitable foundation (not shown). The base frame structure 10 is` generally rectangular in form and has an open forward portion 11 adapted to be positioned over an oil well (not shown) to accommodate a polished rod 12 to be extended into the wall and have connection with the sucker rods and oil Vwell pump valve and plunger for operating the pump to pump oil from the oil well, in a manner well known to those skilled in the art and no part of our present invention so notherein shown or described further.

The base frame structure 10 is shown as having a tripod 15 supported thereon and extending upwardly therefrom and forming a support for a hydraulic operating cylinder' 16 on a support plate 17 at the upper end of said tripod. The cylinder 16 has a 4piston 19 movable therein, having a piston rod 20 depending therefrom through the piston rod end of the cylinder 16. A clamp'21 is detachably connected to the lower end of the piston rod 20 and forms a means for clamping the polished rod 12 thereto, as will hereinafter more clearly appear as this specification proceeds. Y

The base frame structure 10 is herein shown as having a generally rectangular base having angle irons 22 extending along opposite sides of the bottom of a rectangular tank 23 and beyond the ends thereof to form the open portion 11 in advance of the tank 23. Vertically extending angle irons 24 are secured to the angle irons 22 adjacent the rear ends thereof and extend upwardly therefrom along the rear side walls of the tank 23 and have longitudinally extending angle irons 25 secured thereto and extending forwardly along the tank in vertically spaced parallel relation with respect to theangle irons 22. The angle irons 25 have outwardly extending horizontal legs 26 forming slide rails for a base 27 for the tripod 15. The angle irons 25 are connected with the angle irons 22 at their forward ends by vertically extending angle irons 29 defining the forward. end of the base frame structure 10. The angle irons 29 are braced by gusset plates 30 extending upwardly along the angle irons Z9 and outwardly therefrom and connected at their lower ends to laterally extending angle irons 31 extending outwardly fronivthe angle irons 22 andadapted. to be Y secured to a foundation (not shown).

Extending vertically along the back of the tank 23 between the angle irons 24 and connected thereto by a transverse angle iron'28 connecting the tops of the angle irons 24 together, is a channel 32, the legs of which may be welded or otherwise secured to the back wall and the tank 23. vThe channel forms a support for a pair of spaced rails or angle irons 33, connected together adjacent their rear ends by a transverse plate 34. The angles 33 have slots 35 extending longitudinally along the horizontal legs thereof for receiving bolts 36 for holding down a motor 37, and accommodating the motor to be Aadjustably moved along the angles 33, towtake up tension on a belt 39 driven by saidv motor.Y Thejbelt 39 is trained abouta motor'pulley 40 on a motor shaft`41 and 'about aj l drive pulley 43 on drive shaft 44 for a pump 45 for driving said pump. The pump 45 may be mounted on the left hand angle iron 24 and the web of the channel 32. The channel 32 also has a switch box 47 mounted thereview, threaded at its base on the lower end ofthe piston rod 20 and held in position as by a set screw 74. The

on connected with the motor 37 to control operation of 5 base frame structure 10. The rods 49 thus form a three point support for the base 17 and the cylinder 16 projecting upwardly therefrom, supporting said cylinder in position to accommodate the piston rod 20 to support the polished rod 12 through the clamps 21, to passdownwardly through the open central portion of the base 10 The bearing or guide bar 79 thus reciprocably moves along the

rods

81, 81 to form a guide for the lower end into the oil well for connection to the rods and pump therein.

The base plate 27 is shown as having longitudinally spaced inwardly opening guides 51 depending from the bottom thereof at each side thereof. The guides 51 have slidable engagement with the horizontal legs 26 of the angle irons 25, to accommodate the base plate27 and the entire tripod 15 to be withdrawn from the open central portion 11 of the base frame structure 10, when it is desired to pull the oil well, and to accommodate the tripod and base 27 to be secured to the base frame structure 10 in xed relation with respect thereto during the pump driving operation. As herein shown a plurality of nuts and bolts 53, extending through the base plate 27 and the horizontal legs 26 of the angle irons 25 are pro- Avided to detachably secure the base 27 and the tripod 15 in position over the open central portion 11 of the base frame structure 2S. n

The plate 55 is shown as being mounted on the base plate 27 as by nuts and bolts 56 extending through slots 57 formed in the plate 55. The slots 57 afford a means leg of the L of the block 73 is shown as being abutted by a block 75 secured to the block 73 as by machine screws 76. The facing sides of the leg of the L-shaped blocks 73 and the block 75 are conformed to the form of the periphery of the polished rod 12, to clamp said polished rod for vertical movement with the piston rod 20 upon tightening of the machine screws 76. A set screw 77 may be provided to lock the polished rod to the block 73 for reciprocable movement therewith.

Abutting the top of thepolished rod clamp 21 is a bearing or guide bar 79. The guide bar 79 may be threaded on the piston rod 20 prior to threading the polished rod clamp 21 thereon, and is provided with spaced drilled portions 80, which may have bearings (not shown) therein, having slidable engagement with parallel spaced guide rods S1 mounted on the base plate 55 at their lower ends in bosses 83, and at their upper ends in bosses 84 depending from the bottom of the plate 17.

portion of the relatively long piston rod 20, and maintains said piston rod and the polished rod 12 in alignf ment with the center ofthe oil well casing and the sucker rods, valve andpump plunger (not shown) connectedl 79 is an operating arm 8 5 secured to and movable with for adjusting the tripod 15 laterally to accommodate accurate alignment of the clamp 21 with the polished rod 12. The operating cylinder 16 may be of a well known form of high pressure hydraulic cylinder, and, as herein shown, comprises a head 59 bolted or otherwise secured to the top of the plate 17 and extending upwardly therefrom and a vertically spaced head 60 spaced from the head 59 by a metal tube 61. The tube 61 is recessedv within and is secured to the head 59 in leakproof'relation with respect thereto andv is closed at its upper end by a head 60. The head 60 is secured to the head 59 asby tie rods 63 threadedkin the base of the headk 59 and extending through the head 60 and retained to said head by nuts 62 threaded thereon and abutting opposite sidesof the head 60. The head 59 has a pipe coupling 63a connected thereto for supplying fluid under pressurey to the piston rod end of the cylinder 16. The coupling 63a is connected with a vertically extending pipe 64 connected with an elbow 65 connectedwith the pipe coupling' 63 and leading downwardly from the elbow 65 and con-V nected with a deceleration valve 66 at its lower end. The

deceleration valve 66 is mountedon a bracket plate 67,

TheV sleeveV 88 has a spring 90 therein for cushioning` downward movement of the rod 87. A spring 91 encircles the rod 87 adjacent its upper end and is interposed between a collar 92 and an operating lugor stop 93.- The collar 92 is adapted to abut the bottom of the plate 17 upon upward movement of the rod 87 effected by engagement of the arm 85 with the stop 93 to cushion upward movement of the operating rod 87. A second downwardly spaced stop or operating member 94 is provided on the rod87 beneath the operating bar 85. The stops 93 and 94 may be spaced along the operating rod 87 inany desired spacing 'arrangement and are adapted to be engaged by the bar 85 at the extreme limits of movement -of the piston rod 20, to vertically move the operating rod 87 and limit vertical movement of the piston 19 and piston rod 20 in up and down directions as well as effect the reversal in movement thereof.

operatedl by a deceleration cam 69 movable with and secured to the polished rod.12. A breather pipe 70 leads from the head 61 at the head end of the cylinder 16. A return line 71 is shown as leading-from the breather pipe 70 back to the tank 23 to return any uid to tank which may leak past the piston'19 (see Figure 6).

The clamp for the polished rod 12 is'shown Vascom- The operating rod 87 is shown as having two

arms

96 and 97 mounted thereon beneath the stop 9,4. The arm 97 is spaced abovethe arm 96 and extends to one side thereof and `the two arms extend toward the pilot valve 86 for engagementV with

operating levers

98 and 99 of said pilot valve, to operate said valve at the ends of travel of the'pistonrod '20 to effect reversal of the piston 19, as will hereinafter more clearly appear `as this specication proceeds. I

As herein shown, the arm 96 engagesthe lever 98 at the upstroke of the piston rod `20 and is moved into engagement therewith-.by means of engagement of the bar with the stop`93. The larm 97 engages the arm 99at the extreme downstroke of the pistonV rod` 20 and is engaged therewith to operate the valve 96 by engagement of the bar 85 with the lower stop 94.

The pilot valve 86 hasuid connection with a pressure operated shuttle or four way valve for'operating said valve to effect the reversal in travel of the piston 16 along the cylinder 1.9 andthe reversal in the drive to the pump as willmore'clearly appear as the fluid pressure operating ysystem is explained. n

apagada A suction line 101 is shown' asA leadingfrom the tank 23 to a filter 103. A uid conduit 104 connects the iilter 103 to the suction side of the pump 45. As shown in Figure l, the suction line 104 extends across the back of the tank 23'and is connected to the pump 45 from the bottom thereof. A pressure line 105 leads upwardly 45 and return fluid back to the tank 23 as desired. AY

gauge 107 is shown as being connected to the discharge side of the relief valve'106, while a return line 109 is connected from the relief valve 106 to the tank 23.

It will be noted from Figures 1, 3 and 4 that the iilter 103, motor 37, pump 45, suction line 104, relief valve 106 and return line 109 are all connected with the tank 23 and the base frame structure 10 and form a part thereof. A flexible pressure line 110, however, is connected from the pressure side of the relief valve 106 to a check valve 111, which may be preset to accommodate lluid to pass by said check valve in the direction of flow of iluid therethrough at a predetermined pressure, which may be of the order of 65 lbs. (Figure 6). A exible conduit or return line 112 is likewise'shown as being connected from a T 113 to the return line 109 through a tting 115.

The exible pressure and return

lines

110 and 112, respectively, are shown as being looped in the form of slack loops so the base 27 and tripod 15 may be slidably moved along the rails or horizontal legs 26 of the angle irons 25 to position the cylinder 16 and piston rod 20 over the oil well casing for connection to the polished rod 12 or may be moved rearwardly along the legs 26 of the angle irons 25, to position the cylinder 16 and piston 20 to accommodate the well to be pulled without disconnecting the hydraulic system, or interfering therewith.

Referring now' in particular to Figure 6 and the hydraulic control system, a pressure line 116 is connected from the pressure line 110 on the upstream side of the check valve 111-to the pilot valve 86, to supply uid under pressure thereto. A pressure line 117 is connected from one side of the pilot valve 86 to one end of the shuttle valve 100 for operating the piston (not shown) to move to the right and accommodate fluid to pass through a` return line 121 connected with the tank 23 through the return line 71.

t The' shuttle valve 100 may be a four-way hydraulic control valve such as the Model 4150 valve manufactured by Logansport Machine Company Inc., of Logansport, Indiana, and illustrated on page 6a of the Logansport Bulletin dated August 1953. The shuttle valve 100 has the usual piston valve (not shown) operated by hydraulic fluid under pressure on one end of the pisfon valve, to move the piston valve into position to admit fluid to pass through return line 121, and'operated by hydraulic uid under pressure acting on the opposite end of the piston valve for moving the' piston valve in a direction to admit fluid under pressure through a return line 129 leading from said four-way valve.

VAs' shown in Figure 6, the pressure line 117 leads to the left hand end ofthe `shuttle valve 100 and serves to move said shuttle valve into position to admit uid to pass from a pressure line 119 connected in a pressure line 120 leading from the discharge or downstream end of the check valve 111 to the return line 71. Upon the exertion of pressure on the left hand end of the shuttle valve 100, uid under pressure will enter the valve through the pressure line 119 and will leave the valve through the pressure line 121 connected with a ow restriction valve 123 connected with the return line 71 leading-to the tank 23, to return fluid thereto.

The pressure line 120 also leads to and is connected with the deceleration valve 66. The deceleration valve 66 is showrias having a check valve 125 therein accom. moda'ting-vuid under pressure to freely pass through said Y downward movement of said piston.

When the pilot valve 86 is moved into position to admit fluid under pressure to the pressure line 117 at the end of the downstroke of the piston 19 by engagement of the arm 97 on the operating rod 87 with the operating arm 99 for the pilot valve 36, effected by engagementA ofy the operating bar 85 with the stop 93, the shuttle or four-way valve 100 will be moved into position to admit uid under pressure to the line 121 and the ow restriction valve 123. Fluid under pressure delivered from the pump 45 through the check valve 111 will thus pass along the-line 119 through the valve 100 and line 121 and flow restriction valveV 123 and back to tank as determined by the setting of the flow restriction valve 123.

the pressure line 120 through the deceleration valve 66 and check valve 125 therein, along the pressure line 64 to the piston rod end of the cylinder 16, to admit fluid under pressure thereto and effect vertical movement of the piston 19 and piston rod 20 upwardly along the cylinder 16, raising the polished rod 12 and the sucker rods, valve and pump plunger (not shown) connected thereto to effect the lifting stroke of the oil Well pump.

It should here be understood that the control of the lifting stroke of the cylinder 16 and piston 19 is solely through the restriction valve 123 by-passing Huid under pressure from the line 120, and that said ow restriction valve may be set in accordance with the desired speed of travel of the piston 19 and the piston rod 20, to compensate for various types and viscosities of oils being pumped.

At the upstroke of the piston rod 20, the arm 85 will engage the stop 93, lifting the control rod 87 against the spring 91 and bringingthe linger 96 into engagement with the operating lever 98 for the pilot valve 86. This will move the Ypilot valve 86 into position to supply fluid under pressure to a pressure line 127, connected with the opposite end of the shuttle or four-way valve 100 from the pressure line 117. The admission of uid under pressure through `the pressure line 127 to the shuttle or four-way valve 100 will move the valve piston of said valve into position to admit fluid from the line 119 to ow through the return line 129. The return line 129 has a flow restricting valve 130 connected therein which is connected at its discharge or downstream side with the return line 71.

The ow restriction valve 130 is provided to control the speed of downward travel of the piston 19 and piston rod 20 by restricting the flow of uid returned from the cylinder 16 through the line 120 and the fluid by-passed from the pump through the lines 119 and 129.

The pressure line 127 also has a ow restriction valve 131 connected therein. The iiow restriction valve 131 is provided to restrict the ow of fluid under pressure to the four-way or shuttle valve for operating the same, and to elect slow reversal of the shuttle or four-way valve 100, so as to avoid shutter or chatter in the hydraulic line.

The flow restriction valve 131 may be set in accordancev with the viscosity of the hydraulic uid used.

When the shuttle or four-way valve 100 has been positioned to admitnuid under pressure from the line 119 through the valve 100 and through the line 129 and How restriction valve 130, the piston 19 may move down-v wardly along thecylinder 16 by the weight of the piston, the piston rod 20, the polished rod 12 and the pump plunger and valve in the well as well as the sucker rods connected thereto. During downward travelrof the piston ating to supply uid under pressure to the pressure 'line' vAt the same time uid under pressure will pass along 120 which ishy passed back to thetank through the fourway valve 100. The piston 19 in turn forces uid from the head end of the cylinder 16 through the pressure line 64 and through a ow restriction valve 135 in the deceleration valve 66, which is also by-passed back to the tank through the four-way valve 100.

Fluid under pressure thus passes through the line 120 against the pressure of lluid being supplied by lthe pump 45 and by-passed through the four-way valve 100 and is by-passed with the fluid supplied by the pump through the return line 129 and flow restriction valve 130 to the return line 71. Fluid under pressure is thus forced from the piston rod end of the cylinder 16 against the full volume of fluid discharged by the pump 45, all of which is by-passed to tank through the flow restriction valve 130. This volume of uid delivered by the lpump acting against the fluid expelled from the cylinder 16 upon downward travel of the piston 19, provides agreater volume of fluid than is normally in the cylinder 16 Vbe-V neath the piston 19 and in the pressure lines 64 and 120, which provides an accurate control for downward move# ment of the piston 19, the polished rod 12, the pump plunger and valve connected thereto, and enables a more sensitive adjustment to be made in the flow of oil from the well.

,It should be understood, however, that where the back pressure in the lines 110 and 120 may build up to a value that would prevent down travel of the piston 19 at the required rate that lluid is by-passed from the pump back to tank through the relief valve 106 and thel return linc109. The deceleration valve 135 is shown as being operated by the cam 69 on the polished rod 12. The cam 69 is shown in Figures 1 and 2 as being mounted on the polished rod 12 just beneath the clamp 21 andas having a sloping cam face sloping outwardly as it extends upwardly along the polished rod 12. As herein shown, the cam 69 comprises a lower disk 137 and an upper disk 138. The disks 137, 138 are connected together by a plurality of sloping stakes 139, one of which serves as a cam surface engaging a plunger 140 projecting from the body of the deceleration valve, for depressing said plungerv adjacent the lower portion of the downward stroke of the piston 19. The cam 69 thus moves the plunger of the deceleration valve 66 inwardly to restrict the tlow of iluid'past said valve 135 and gradually cuts of the flow of hydraulic fluid from the cylinder16, until it is completely cut oi at the bottom of its stroke. This cushions the piston 1.9 at the bottom of -its stroke, causing it to stop gently and thus avoids sudden jars to the piston 19,` the piston rod 20, the polished rod 12, and the sucker rods, plunger and valve connected thereto and operated thereby.

As the piston 19`reaches the bottom of its stroke, the operating bar 85 will come into engagement with the stop 94 and depress the operating rod 87,causing the finger 97 to engage the operating lever 99 of the pilot valve 86 and move rsaid pilot valve to admit Vfluid* under pressure through the pressure line 117 and shut ofi the flow of fluid through the pressure line 127. This will l supply uid under pressure to move the shuttle or fourcylinder 16 to lift the piston 19, the piston "rod 20, andl polished rod 12, suckerrods, pump plunger and valve operated thereby at a rate controlled by the ow restriction valve 123.

It may be seen from the foregoing that

thevilowV restriction valves

123 and 130 may accurately control up and down movement of the piston 19 and maybe ad justed to suit varying-types of crude oil soas to eliminate foaming of the `oil being pumped vfrom the well and thus 8v avoiding thedest-roying or reducing lthe quantity yof the oil; pumped due to the foaming thereof.

ItA may further be -seen thatthe two stops 93 and V94 may jbe readily adjusted for any required length of stroke g and `that by adjusting the length Vof stroke of the piston 19", the required production from the well may be attained.

With reference to Figures 5 and 6 it may be seen that a pushbutton switch 143 is provided in conductors 144 and l145for energizing the motor 37 to start the same. This switchis in the starting box 47. A limit switch 146 is connected in a conductor 147 connected across the contacts of the pushbutton switch 143. The limit switch 146 is biased into an open position, to enable the motor 37 to be stopped upon depression of the switch 143, and is engageduby a cam surface 149 on the lever 99 during the upstrokeV of the piston 19. The cam 149 serves to close the `limit :switch 146 and to hold the limit switch 146 closed until the piston 19 has reached the upper end ofitsstroke and the stop 93has been engaged by the arm 85, to eiect operation of the lever 98 and shifting of the piston valvev 86 into position to admit uid under pressure through the pressure line 127, to operate the four-wayA valve to eifect the return or downward stroke of the piston 19. Thus theswitch 146 actsA as a holding switch andprevents stopping of the motor 37 by operation of the push button 143 during upward travel of the piston 19. This prevents manual stopping of the pump upona partial upstroke of the piston 19 and assures that the pump can onlybe manually stopped at the selection of the operator on its downstroke.

It may be seen-from theforegoing that we have provided a simple land eicient form of pumping or operating unit particularly adapted for operating oil well pumps which-may readily be setin place, and then when once set in place, the cylinder 16 and its supporting tripod 15 may readily be moved back when it is desired to pull the well, without disconnecting the cylinder and control valves therefor from their source of hydraulic lluid under pressure.

It may further be seen that the actuating unit is operated by the direct flow of hydraulic fluid to the lower or pistonrod end of the cylinder 16 and that up and down movement of the hydraulic cylinder and piston is accurately controlled by the passageof uid through the

ow restriction valves

123 and 130, and that the shock to the well rods is eliminated by the cam 69 actuating the flow restriction valve at the lower portion of the downstroke of the piston 19.

It may further be seen that excessive pressures are relieved by lthe relief valve 106 and that the general circuit arrangement is such as never to be overtaxed or to cause excessive heating of the oil.

It may still further be seen that the system always provides pressure to lift the piston 19 and that the motor 37 cannot be lshut oi even by operation of the pushbutton switch V143 as long as the piston 19 ison its upstroke and until said piston has made a complete stroke and starts on its downstroke. i

lt will be understoody that modifications and variations of the present invention may be effected without departing from the spirit and scope of the'novel coni cepts thereof.

, We claim as our invention:

1.. In a fluid pressure operated power unit particularly adapted for reciprocably driving oil well pumps and the like, a base, a vertically extending cylinder supported onsaid baseV in vertically spaced relation with respect to ythe ground, a piston reciprocably movable within said cylinder and having a piston rod depending therefrom, -a tank, a pump connected with said tank, a motor for driving said pump, a pressure lineleading from said pump to the piston rod end of said cylinder, a relief valve in said pressure line having connection with said tank, a `return line connected with said pressure line downstream of said relief valve, a uid pressure .Operated control valve connected with said return line, `an exhaust line leading from said valve and having connection with said tank, a ow restriction valve in said exhaust line, said iiow restriction valve in said exhaust line controlling the rate of downward movement of said piston, a pilot valve connected with said pressure line and supply fluid under pres sure to said control valve to operate said valve to direct fluid through said exhaust line in accordance with the position of said valve, means for operating said pilot valve at the end of the lifting strokes of said piston to supply liuid under pressure to said control valve to elfect Ithe reversal in travel of said piston, an energizing circuit for said motor having a starting switch therein, a normally open limit switch by-passing said starting switch and holding said motor from stopping by operation of said starting switch as long as said limit switch is closed, and means operated by upward travel of said piston for closing said limit switch to provide a holding circuit around said starting switch and hold said motor energized until said piston has reached the end of its lifting stroke and has reversed its travel to start on the lowering stroke thereof.

2. In a fluid pressure operated power unit particularly adapted for reciprocably driving oil well pumps and the like, a base, a cylinder supported on said base, a piston reciprocably movable within said cylinder and having a piston rod extensible -therefrom to effect a lifting and lowering operation upon reciprocable movement of said piston, a tank, a pump connected with said tank, a motor for driving said pump, a pressure line leading from said pump to the piston rod end of said cylinder to supply iluid under pressure to said cylinder to effect a lifting operation, a relief valve in said pressure line having connection with said tank, a return line connected with said pressure line downstream of said relief valve, a uid pressure operated control valve connected with said return line, an exhaust line leading from said control valve to said tank, a pilot valve connected with said pressure line and operated by movement of said piston rod to supply flu-id under pressure to said control valve to operate said control valve, to elect lifting and lowering of said piston and piston rod, said pilot valve being maintained in position to effect lifting of said piston rod by the pressure of uid acting thereon, an energizing circuit for said motor having a starting switch therein, a normally open l-imit switch by-passing said starting switch and holding said motor from stopping by operation of said starting switch, as long as said limit switch is closed, and means operated by travel of said piston and said piston rod upon the lifting strokes thereof, for closing said limit switch to provide a holding circuit around said starting switch to hold said motor energized and maintain pressure on said pilot valve to eiect the lifting stroke of said pis-ton until said piston has reached the end of its lifting stroke and has reversed itsrtravel to start on the lowering stroke thereof.

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