US2572748A - Hydraulic pumping unit - Google Patents

Description

Oct. 23, 1951 P. E. Nou. ET A1. 2,572,748

HYDRAULIC PUMPING UNIT J8 f M 102 l 94 ToAccuMuLAron. g

f3 ro Risenvom I FROM CYLINDER.

LINE C2 INVENTORS 276 0m/L Nou.

man cnmnea MNE Ca mom Pump By ZW///- ,qu-Q

Ma/4x9 Oct. 23, 1951 P. E. NOLL ET AL HYDRAULIC PUMPING UNIT 5 Sheets-Sheet 2 Filed NOV. 6, 1948 Oct. 23, 1951 P. E. NoLl. ET AL 2,572,748

HYDRAULIC PUMPING UNIT Filed Nov. 6, 1948 3 Sheets-Sheet 3 t JM Jeff Lowfa UPR. No oF .5 3.5 f" j Acca .-DECEL.

Patented Oct. 23, 1951 UNITED STATES PATENT QFFlj-)CE 2,572,748 HYDRAULIC PUMPING'UNIT Application November 6, 1948, Serial No. 58,714 aolaimsl (C1. 6'0"-5'2) Our invention relates. to.` hydraulic pumping units, and has particular reference to.. a. precise control circuit for controlling the actuation-of. a ram. in a hydraulic cylinder, which` ram' may be usedr for exampleY to actuate a reciprocating mechanical pump'- disposedy in` an oil well;

The principal componentsl of our hydraulic system are similar tov those disclosed' in patent application Serial No. 668,942, iiled May*10; 1946, in the .names ofA Paul E. Noll, CharlesW. Crawford, T; DwightAller, and Albert R. Retheyf,` and Which. issued as Patent No. 2504218, April 18, 1950. In general, a prime mover drives a pump which takes hydraulic fluidfrom a reservoirr and delivers it under pressure to' a four-wayfvalve. The valve alternately connects opposite ends ofa hydraulic cylinder to the'v pressure ui'dfand to exhaust,y to cause the piston in the'cylinder tofbe reciprocated. The ram connected to the piston may be coupled directly or indirectly to a pump, and for oil well pumping may be coupled to the upper end of ar string of' sucker rods, the lower end of which may be connected to a pumpl dis' posedv deep Within an oil well. Anaccumulator' is customarily provided to assist on the pumping stroke of the unit and thereby reduce: the-*maximum pressure required from the pump and in addition substantiallyv equalize the pressurerequired from the pump on the pumping stroke and the return stroke of the ram; that is, on the re` turn stroke the pressure of the accumulator opposes the pump pressure.

Our invention includes a novel circuit for controlling the reversal ofA the hydraulicl ram:v at the ends of each stroke. Due tothe inertiaI of tlie sucker rod string and? thecolumn of'- oil being lifted, stresses of serious consequence may-be iinposed on the rods lay-rapid reversalsfat th-eends of 'eachstroke.v It is highlydesirable; therefore, that theA rods be'deceleratedI andA accelerated very gradually, particularlyv at the lower reversal. This gradual deceleration and acceleration may be accomplished in accordance with lour invention by by-passing pressure fluid'v at the extremes of travel of the ram so that the volume ofthe uid passing throughthe four-way control valve is reduced, thus gradually slowingA` the ram toa stop.

In order to permit close spacing of the subsurface oil pump, thus reducingA its clearance and y ployed to establish the reversal point,"but instead l thei piston is :hydraulically suspended throughout the reversal'. Since the counterbalance pressure tends to assist in decelerating the ramat the bot;- tom reversal, variation in, that pressure might cause variation in the reversal point. We regulate,l precisely the lower end point or travel of, the piSllOILby maintaining the counterbalance pres,- sure within close limits by building up or: relieving gas pressure according to Whether there is over-travel or under-travel of the piston; With re,- spect to.- ai preselected bottomv reversalv point. 'thus the, counterbalance pressure is utilized; asv a control-Vmedium for end. reversal point, and our invention provides apparatus: for continuously .ande automatically controlling this; pressure;V

It isrtherefore an object of our invention 'to providergradual accelerationand deceleration of the rram in. a hydraulic actuating. cylinder by shunting or lov-passing pressure fluid Another object of our inventionr is to. provide a; hydraulicy pumping unitxincorporating a. bypa'ss. action and a four-way valveenergizedat the same time by means of a single mechanical. elementassociatedf with thestroke of the actuating ram. y

A furtherv object ofour invention is, to. provide a hydraulic actuating unit with a by-passvalve anda four-way valve wherein a time delay device is coupledwith the four-.Way valve to permit synchronized actuationv of the by-passvalve andthe four-:way valve to effect deceleration, reversal, and'V acceleration.

A further object of our inventionistopfprovide a hydraulic pumping unit incorporating a counterbalancing device of the compressedigas type, withV means for automatically. maintaining the gas r pressure.

Still-another object oifour invention issto pr'olvide a hydraulic actuating -un-it inlwhioh the pistonis hydraulicallysuspended throughout its reversals and in whichmeans are provided to. prevent variation in the lower reversal` peint.l

Another object ofV our invention is to provide-a hydraulic pumping unit in which variation of the lower reversal pointV is` prevented by automatically increasing or reducing the counterbalance pressurefaccording to Whether the pistonj tends to over-travel or under-travel a preselected reversal point.

It is also'a feature of our invention to provide an automatic'loW-coritrol valve in the counterbalance circuit to prevent darn-age toftheunit incase of breakage-,oi the rod string;

Other objects and advantages-of Vour invention will be apparent in the vfollowing description and and secondary pilot valves of Fig. 2, which mechanism is illustrated schematically in Fig. 2;

Fig. 3 is a circuit diagram of the accumulator pressure control circuit illustrating the circuit` components in section;V

trative time delay valve and a four-way'valve to which the time delay valve is connected; and

Fig. 5 is a sectional View through an illustrative by-pass valve that may be utilized in the circuit of Fig. 2. Y .Y i

General description A presently preferred commercial actuating unit is illustrated in Fig. 1, wherein a .pumping unit l0 is mounted on a frame II that mayroll on rails I2 when it is desired to withdraw the unit as a whole from the vicinity of an oil well having a ilow tubing I3 projecting above the ground. The pumping unit IIJ includes a vertically disposed hydraulic actuating cylinder .I4 with an actuating pistonor ram I4a axially slidable therein and a T-shaped sprocket head I5 mounted on the top end of the ram. Over a pair of horizontally spaced sprockets I8 is trained a chain I1, one end.of which is anchored at I9a to a dead-end rod I9 and the. other end of which is attached to a polish rod 21 by means lof aclevis I6. The actuating cylinder I4 is supported in an upright position by meansY of inclined braces 2l. Y.

The actuating ram I4a is operated byhydraulic iiuid under pressure supplied by a pump 23,.and 45 Vv23, and the pressure fluid control valve operating mechanism is actuated by a trip rod 26 secured to the sprocket head I5.

The clevis I6 on the chain I1 is coupled to a polish rod 21 acting as the terminalsection. of a string of sucker rods passing downwardly through the flow tubing I3a to contact a reciprocating pump (notl shown) disposed below the oil level within the oil well. A stuing box 28 secured to the top end of the tubing I3a seals` off the polish rod 21 from the ilow tubing I3 to prevent leakage therefrom, and a suitable connection (not shown) to the flow tubing I3 leads the pumped oil to a suitable reservoir or tank. Thus the entire hydraulic pumping unit I0 causes a pumping action by means of the reciprocation of the sprocket head I5 by the actuating ram Illa which causes the chain I1 to raise and lower the polish rod 21 to thereby actuate the pump within the oil well and lift a column of oil in the flow tubing I3 to the earths surface. 4

The details of the hydraulic circuit of the pumping unit IU of Fig. 1 are illustrated in Fig. 2. There it will be noted that the pump 23 receives hydraulic fluid from a reservoir 29 and fio 4 delivers the uid under pressure to an outlet pipe 3| connected to a relief valve 32, a by-pass valve 33, and a four-way valve 34. An exhaust or return conduit 35 connects these three valves to the reservoir so that the same hydraulic fluid may be continuously circulated. The four-way valve 34 is actuated to connect two cylinder lines CI and C2 alternately to pressure and to exhaust, and accordingly reciprocates the actuating ram I4a inasmuch as these conduits are connected to opposite ends of the cylinder I4. The hydraulic ram unit comprises a stationary outer shell36 having a concentrically mounted tube 31 projecting upwardly therein, to the lower end of vwhich is attached the pressure line C2. A tubular Vpiston 38 integrally formed on the lower end of the ram Illa makes a sealing engagement Fig. 4 is an enlarged sectional viewhof'an'illusf with the interior ofthe shell 36 and the exterior of the tubing 31 and reciprocates therebetween, the closed upper end of the ram I4a being attached, to the sprocket head I5. Thus the eiective lifting area for pumped fluid is the outside diameter of the central tube 31, which area may be designated as AI. The effective return stroke area of the piston 38 is the annular space between the ram I4a and the outer shell 36, to which the pressure supply line CI communicates, and which area is designated as A2. The area A2 is preferably and usually made smaller than the area AI so as to effect a rapid return of the piston as compared to the working stroke speed of travel, assuming a constant delivery output from the pump 23.

The piston 38 isv normally urged upwardlyby means of pressure existent Within the accumulator 22 acting Von the bottomof the, piston 38. Thus the accumulator 22 may be provided with van outlet tube 39 coupled to a flow tube 4I that communicates with the interior of the cylinder shell 36. The coupling of the flow tube 4I with the outlet tube 39 is enlarged to form a valve seat 42 for a surge poppet valve 43 normally urged to an open position by means of a compression spring 44. Thus a normal flow of hydraulic fluid from the accumulator to the ram will not cause operation of the poppet valve 43, but if the chain I1 should break or the string of sucker rods should break, release of a load would cause` rapid rise of the piston 38 with a consequent rapid flow from the accumulator. This rapid flow would in turn cause the poppet valve 43 to seat, thus stopping flow from the accumulator through tubes 39 and 4I, and causing the piston 38to move to its upper end position vat a slow rate of speed regulated by valve II8. Thus breakage due to the piston striking the packing gland at the upper end of the shell 36 is avoided. In passing, it should be noted that thevaccumulator 22 is of the usual type wherein a gas under pressure occupies the upper portion of the accumulator to act upon a hydraulic fluid disposed in the bottom part of the accumulator tank.

As previously mentioned, our control circuit obtains a deceleration' at the end of each stroke and a gradual acceleration at the beginning of each stroke by means of by-passing pressure fluid to exhaust, thereby diverting from the four-way valve its normal volumetric fluid supply and also decreasing pressure-to the four-way valve. Thus the ram I4a, at the end of, each stroke, receives a vdecreasing supply of iiuidunder pressure, vthus causing it to slowdown to a stop;Y In this way the momentum of the loads being carried is lgradually decreased so asto, provide asmoothrevversal with, rod' stresses. k5 Whileit agregame i' woul'djbel possible to provide two projections on the -triprod 26-adjacent each end so that the bypass' valve could1 be operated prior to the operation-of the four-way valve,- we prefer to initiate theY action of both valves at the same time by a single projection at each end.

Thus the trip rod 26 is provided with an upper projection 26a and a lower projection 25h to act on a bell crank 45 illustrated in more detail in Fig. 2a wherein it will be noted that one arm of thel bell crank is bifurcated and the fork tips oiiset as at 45a and 45h. Accordingly the two projections or iingers 26d and 26o are disposed in .diiierent vertical planes so that the lower projection 26h will contact only tipA 45a, and the upper projection 26a will contact only the other tip 451).V Thus the fingers 26a and 26h contact a tip and operate the bell crank to one extreme position or the other, at which position the tip will be disposed out of the path of travel of the particular actuating linger so that the linger passes the bell crank. Upon the next reciprocation the linger that had just actuated the bell crank and traveled past it would again travel past the bell crank without operating it, but the other tip of the bell crank would be in the line of travel of the other linger or projection. From the foregoing it will be apparent that the neutral position illustrated in Fig. 2a is never achieved as a rest position, `inasmuch as the bell crank 45 should be in one extreme position or the other. This attainment of an extreme position that will rotate the tip just actuated out of the path of travel of the acuating linger may be assisted by an over-center compression spring 461 contacting a portion of the bell crank 45.

We also prefer to operate the by-pass valve 33 and four-way valve 34 by means of pilot valves rather than by direct mechanical actuation. The

bell crank 45, for this purpose, is connected by a link 46 to the control handles of a primary pilot valve 41 and a secondary pilot valve 48. Both the pilot valves 41 and 48 are simple four-way valves, and are illustrated as being of the rotary type. The primary valve 41 is connected to pressure and to exhaust by means of conduits 49 and 5I, respectively, thus giving a unidirectional supply to the primary pilot valve. The secondary pilot valve 48 is, by contrast, connected by conduits 52 and 53 to the cylinder lines Cl and C2 so as to obtain alternating pressure and exhaust c onnections. The cylinder lines of the secondary pilot 48 are connected through metering valves 54 to opposite ends of the pressure-driven by-pass valve 33. The cylinder lines 56a and 51a of the primary pilot valve 41 are connected, however, to opposite ends of a time delay or relay valve 55 which, after a time period of an appreciable duration, supplies pressure andexhaust to opposite ends of the four-way valve 34 through lines 56h and 51h.

From the foregoing description itwillbe apparent that a single linger 26a or 26h on the trip rod 26 may initiate the actuation of the by-pass valve 33 and the four-way valve 34 at the same time, but because of the interposition of the time delay valve 55, the actuation of the four-way valve 34 will be delayed until immediately following the traverse of the by-pass valve 33. Furthermore, as will be apparent from an inspection of Fig. 5, the by-pass valve 33 has a time-graduated capacity so that at the end of the delay period of the time delay valve 55, the by-pass valve 33 will b'e passing substantiallyall of the output ofk thepump 23'. The timev delayvalv'e' 55 is' controlled by adjustments indicated-11ml Eig.: 4 to-co'ntrolits rate of speed, and themeter valves 54 in the circuit of by-pass valve' 33 areL also manually adjusted -so that the -time of full. ii'ow of thev vby-'pass valve 33 will coincide with. the period ofthe time delay valve 55. Also the posi'.- tionof trip fingers 26a and. 26h on trip rod. 26 may' be adjusted in conjunction with the valves togive-an acceleration and deceleration travel of any desired length.

The control of the pressure in the accumulator 22 is also illustrated diagrammaticallyin. Fig.. 2.. Thus if there is a deii'cient pressure withinl the accumula-tor 22,.a make-up pump 58fis automaticallyE operatedl to pump air into a line 259. con.- nected to the accumulator 22.- ()n theother hand, if thegas pressure of the accumulator is excessive, ablowdown valve 6| is operated automatically to release air or other gas from.y the accumulator 22 through a conduit 62. The main control element of the accumulator pressure circuit is a stroke control valve 63 which is urged upward by hydraulic iiuid under pressure supplied by a conduit 64 and which is mechanically driven downwardly by the sprocket head l5 acting through a vertically disposed drive rod 65, the top end of which is positioned so as to be engaged by the head I5 as it nears the lower extremity of the-stroke.

I Detail description of power clutch The detail construction of the power circuit may be explained withl reference to Figs. 4 :and 5*, Vas well as to Fig. 2. Referring to Fig. 4, it will 'be noted that the time delay valve 55 includes a barrel 66 having an exhaust port 61 and two cylinder ports 68 and 69. The exhaust line 5|. is connected -to the port 61, and the cylinder lines 51h and 56h are connected to the ports 68 and 69, respectively. The opposite ends of the barrel 66 are closed with identical-caps 1|, including pipe iittings 12 communicated by means of check valves 13 to the interior of the barrel 66. The check valves :are by-passed by adjustable needle or metering valves 14a and 14h. A double-landed spo-o1 15 is slidably disposed within the barrel 66 to reciprocate between the two end `caps 1|. When pressure fluid from primary pilot valve 41 is applied at one end of the time delay valve 55, for example the left end, it flows through the check valve 13 to the interior of the barrel 66,

forcing the spool 15 to the right, and the Huidtrapped at the right end of the valve isforced outwardly through the meter valve 14a. When the spool has moved to the right suihciently to uncover port 68, there will be a direct communication between the left hand line 51a and its associated line 51h, `and the pressure fluid wil-l pass through line 51h to shift four-way valve 34. The length of time delay between the application of pressure fluid to the left hand end of the time delay valve 55 and the shifting of the fourway valve 34 is governed by the rate of metering of exhaust uid through the meter valve 14d'. As the spool 15 moves to the right, the line 56h will be communicated to the exhaust line 5i. When the pressure from the primary pilot valve 41 is reversed, the valve moves to the position illustrated in full outline in Fig. 4, communicating the line 511) to exhaust and interconnecting lines 56a and 56h. The time delay as the valve spool moves to the left is governed by the rate of metering of exhaust fluid through the meter valve 14h. A

' An illustrative four-way valve 34 for operation with the system is also indicated in Fig'. 4.- This `valver includes a main housing16 havingya cenjf tral bore 11 in which is disposed a Adouble-landed spool 18, which spool is provided with projecting ends 19a that act as pistons. The housing .16 has two cylinder ports formed therein to which the lines CI and C2 are connected, and alsorhas acentral pressure port 19 disposed betweenthe two cylinder ports. Exhaust i'luid is discharged through a bifurcated exhaust passage 8| to which the exhaust pipe 3'5 is connected. The housing 16 also has cylinder chambers 82 formed at either end thereof communicating With the actuating lines 56b and 51h. In the position illustrated, cylinder line C2 is connected to pressure port 19, whereas vcylinder line CI is connected to exhaust conduit 35. If the pressure and exhaust in actuating conduits 56h and 51h are reversed, the spool 18 will slide toward the right to reverse this condition of flow. Y

An illustrative construction for the yby-pass valve 33 is shown in Fig. 5, wherein it will be noted that a housing 83 has'ports 84 at each end lto communicate with the lines from the secondary pilot valve 48. The housing 83 also is provided centrally with axially spaced ports 85 and 86 communicated to the pressure pipe 3| and to the exhaust pipe 35, respectively. A doubleheaded piston 81 is disposed within the'housing 83 to move in response to the direction of application of pressure and exhaust atthe ports 84, and has one head slotted with tapering grooves 88 to provide a condition of graduated flow from pipes 3| to 35 as the piston 81 moves in the bore. The rate of speed of movement of the piston 81 may be carefully regulated by the meter valves 54 (Fig. 2). An adjustable threaded stop 89 is provided to establish the maximum flow conditions through the valve when the piston 81 is at the full flow position illustrated. As previously mentioned, the secondary pilot valve which operates the by-pass valve 33 has its inlet and exhaust pressures reversed by reversal of the four-way valve 34 due to the connection to lines CI and C2. Forthis reason the spool 81 will be returned to a nonflow or non-by-pass condition shortly after the four-way valve has been operated.

Detail description of accumulator pressure control circuit The detail construction of the accumulator pressure control circuit is illustrated in Fig. 3, wherein the parts previously identified in connection with Fig. 2 are illustrated, including the main control element, the stroke control valve 63, as well as the make-up pump 58 and the blowdown valve 6|. The stroke control valve 63 includes a valve housing 9|, a dashpot housing 92, and an actuating cylinder housing 93 Vairranged end-to-end in axial alignment. A central stem 94 passes through all three housings and has a reduced portion 95 at the valve housing 9|, a check valve piston 96 disposed in the dashpot housing 92, and a piston head 91 dis posed within the actuating cylinder 93. Pressure is supplied to the valve 63 by means of the con. duit 64, previously identified, communicating with the fluid pressure pipe 3|, which pressure fluid passes through a check valve 99 to the actuating cylinder 93 to force the stern 94 upwardly. A branch conduit 98 supplies pressure fluid to a port in the valve housing 9|. A second port in the housing 9| is connected to a conduit |02, and a third port |03 is connected to a conduit |04 lleading to the reservoir 29.V

The dashpot 92 of the valve 63 is the central control element of the valve 63 and is provided with an external metering circuit including a conduit |05 and a metering valve |06. The dashpot piston 96 is apertured to permit passage of liquid therethrough on the down-stroke, but has a check valve |01 which closes the aperture on the up-stroke to give rise to the dashpot action. The normal lower position of the stem 94 with the dashpot piston 96 is illustrated in Fig. 3, and it will be noted that it is spaced an appreciable amount from the bottom of the containing cylinders. It will also be noted that in this position, the pressure port |0| remains covered by the stem 94.

As stated previously, deficiency of gas pressure in the accumulator will tend to permit the ram to over-travel its normal point of reversal. Accordingly, the sprocket head |5 in contacting the drive rod 65 will drive it and the stem 94 below its normal position due to the fact that the entire hydraulic cylinder is permitted to drop below its predetermined lower point. The driving of the piston 96 below its normal lower point will cause communication between the pressure port |0| and the conduit |92, causing pressure iiuid to iiow through that conduit to a three-way valve |09, causing a spool in that valve to be raised, as illustrated, against the compression of a spring ||2. In the illustrated position, pressure uid from cylinder line C2 will be Vcom--I municated by a conduit ||3 through the valve |09 to a conduit I4 connected to the bottom end of the hydraulically actuated make-up pump 58. Inasmuch as pressure will exist in the cylinder line C2 on the up-stroke of the actuating ram |4a, this pressure will cause a piston ||5 within the pump 58 to rise, thus compressing air and forcing it outwardly through the conduit 59 to the accumulator 22. At the time that cylinder line C2 is under pressure cylinder line Ci will be subject to exhaust, and accordingly a conduit ||6 connected to the exhaust will permit the piston ||5 to move freely upwardly. Upon the downstroke of the actuating ram Ma, iiuid under pressure will pass through the line l |6 to act on the pump piston ||5, forcing it downwardly because the three-way valve |09 will then be in its rest position because the rise of the stem 94 will close off the pressure port |0| and open exhaust port |03. The spool I|| of the three-way valve will then communicate the conduit ||4 to the reservoir. The over-travel of the ram |4a will continue, and the make-up pump will deliver a charge of air to the accumulator on each stroke until accumulator pressure has been returned to normal.

When the accumulator gas pressure is excessive, the hydraulic ram will tend to under-travel its normal bottom reversal point, and consequently the stern 94 will not be returned to the normalv position illustrated. ,The .normal rise of the piston 96 on its dashpot action will cause the upper end of the stem 94 to Contact a valveoperating lever to actuate the blowdown valve 9| and thereby relieve gas pressure from the accumulator. The under-travel and resulting blowdown will continue on each stroke until accumulator pressure has been reduced to normal.

Operation The operation of the power control'for our pumping unit may best be described with refer# eneiio Fif-1 e119? -.The primemver. 2,4.. ma:

mst mbe energized, causing .the pump 12.3 t0 :be actuated, drawing .fluid vfrom reservoir 29 :and .delverins-ittogpipel. The pump may be ofany suitable type that develops a requisitepressure, .but -we. prefer to use a constantfspeed constantdisplacement jtype vof pump, protected against voverload/by. relief val-ve )32.

`The operation of the ram 14ar is continuous and @automatic and is principally effected by the four-way valve 34 which is connected between ,the pressure line -3I and the exhaust linev35. Accordingly pressure and exhaust alternately .exist in the cylinder lines CI and C2 connected, respectively, to the 'top andthe bottom of the hydraulic cylinder |14. Pressure -in line C2 is .delivered tothe central-tube 31 of -theram and acts over'the-area AI to liftthe ram. Fluid under pressure in the accumulator 22 passes through conduits 39 and 4I to act on the bottom ofthe piston 38. The entire sprocket'head -I5 is consequently lifted, causing a twofold movement of T thechain l1 connected by the clevis lto the `polish rod 21 .of the oil Well.

When the actuating ram '14a approaches the end o f its stroke, theiinger'Z'Bb on `the trip rod .26 connected to the sprocket head I5 engages the -bell v'crank 145, shifting the link 46 andconsequently shifting rthe pilot valves 41 and 48. The pilot valve 41 iacts to reverse the four-way .valve 34, .but this .actuation is delayed Abecause of the. interposition of the *time delay valve 55 in .thecircuiu as is best'illustrated in Fig. 4. The actuation of the by-pass valve 33 is started immediately by delivery of fluid under pressure to the rightehand end (Fig. 5) ofthe by-pass valve 33, causing its piston 81 to shift to the left to the position villustrated in Fig. 5. This .shift vis not immediate, however, but vis slow `in `acting due to the control of vthe rate of exhaust as determined by the `setting of the meter-valve 54.

The flow vof iluid to actuate the by-pass valve 33 to decelerate the ram as its approaches the end'of Vits downstroke can b e traced from the cylinder line CI, via pipe 52, secondary pilot valve 4 8, ,meter valve 5.4 at theright, and port 84 Aat the right into the right end of cylinder `3.3. .The left'end of this cylinder isrelievedvia port 84 at theleft, meter valve 54 at the left, secondary pilot .valve .48,.and pipe 53 to cylinder line C2. The vi low. to actuate this valve todecelerate v the fram as it approaches the end of its upstroke is similar, exceptthatthe actuating uid comes'from cylinder line C2 and pipe 53 andthe valve gis relieved to pipe 52 and cylinder line CI.

The effect of the opening of the by-pass valve 33 is to divert from the four-way valve 34 a part of the normal output of the pump 23. As the hydraulic cylinder approaches its upper stop, an increased amount is by-passed due to the movement of the piston 81 to the left until finally only a small flow of iiuid is left for the four-way valve '34. The effect-is a'gradual slowing of the piston 38 of the -ram Ma, causing a slowing of the associated string of sucker rods and the column of o ilbeing lifted tothe surface. Thus, reversal o f :the rods is vaccomplished gradually at the ends ofthe stroke,with minimum reversal stresses induced therein. As the ram piston `38 reaches the end of its upward travel, the time delay valve 55 will'permit the control fluid from the pilot valve 48 to shift the four-way valve 34, and accordingly this shifting of the valve will take place under a reduced pressure and a refi10 Y d1-iced. .fluid,flow rvcondition, .thus relieving the .valve or" major loadsduring movement.

The `flow of fluidftoactuate the yby-pass .valve ,33 to accelerate tjlieram as itstar-ts its upstroke can b e-traced from .the cylinder line C`2,-via pipe :53, secondary lpilotvalve 48, meter valve 54 at .th e left, and port 84 at the left .into vthe left end of ycylinder 83. The right end of Athis cylinder is relieved via port 84 at the right, meter valve -54 at the rig-ht, secondary pilot valve 48, and pipe 5 2, to cylinder line CI. The -flow to actuate this valve to accelerate the ram as it starts its downstroke is similar, except that the actuating fluid comes vfrom cylinder line CI and pipe 52 and A'the ,valve is relieved to pipe 53 and cylinder AlirleC'L While we have shown and described the preferred embodiment of our invention, we do not desire to be limited to any of the details shown and described, except as defined by the terms ofthe followingclaims We claim:

y1. A hydraulic pumping unit comprising: a reservoir; apower driven pump receiving fluid from the reservoir; a four-way valve having a pressure .port connected'to the pump output and having an ,exhaust port connected to the reservoir; a cylinder containing an actuating ram and being connected to the four-way valve for reciprocation of the ram, a by-pass valve connected between the pump output and the reservoir in parallel with said four-way valve; an automatic .actuatorfor voperating the by-pass valve as the ram approaches the end of each stroke in either direction,zwherebythe fluid delivered to the four- Way vrvalve is gradually reduced to decelerate the hydraulic ram prior to reversal and gradually increased to accelerate the ram after reversal; and lan automatic actuator for operating the four-wayvalve at the end of eachstroke to cause the reversal of `theram.

12. A :hydraulic pumping unit comprising: a reservoir; va power driven pump receiving ifluid from 7the reservoir; a foureway valve connected to the pump output and to the reservoir; a, cylinder containing an actuating ramand'being hydraulically connected to the four-way valve for recipro'cation of the ram; a by-pass valve connected between the pump output and the reservoir in parallel with said four-way valve; a single mechanical actuator mechanically coupled to the ram formovement inresponse to ram actuation andadapted to initiate operation of the by-pass valve and the four-way valve near the end of each stroke of the ram in either direction; and atime delay mechanism for the four-way valve, whereby the by-pass valve will be first operated to `decelerate ,the hydraulic ram and thereafter the fourway valve will operate to reverse the hydraulic ram, after which the by-pass Valve will operate to accelerate the ram inthe vopposite direction.

3. A ,hydraulic .pumping unit comprising: a reservoir; apump adapted to receive fluid from the reservoir; a four-way valveconnected to the pump output and to the reservoir; a hydraulic actuating cylinder; a pistonand .ram slidable .in said, cylinder ,a pair of vcylinder lines connecting the actuating cylinder to thefour-,way valve ,so that alternate connection of the lines to pressure and exhaust will cause a reciprocating motion of a piston and ram in the actuating cylinder; a hydraulically operated by-pass valve disposed between the pump output and the reservoir in parallel with said four-way valve and normally 11 maintained in a closed position; a pilot valve for operating the by-pass valve by means of pressure fluid from ,theVV cylinder lines; and an actuator for the pilot valve to operate it a predeterminedvdistance from the end of the stroke in either direction, whereupon the by-pass valve will gradually reduce the fluid supply to the fourway valve prior to reversal of the four-way valve to thereby decelerate the actuating ram, and, after reversal of flow in the cylinder lines by actuation of the four-way valve, will gradually increase the fluid supply to the four-way valve to thereby accelerate theactuating ram. g 4. A hydraulic pumping unit as defined in claim 3, including a meter valve interposed between the pilot valve and the by-pass valve to regulate the speed of operation of the by-pass valve,

5. In a hydraulic pumping unit: a source of hydraulic fluid under pressure; an actuating cylinder; a ram in said cylinder; a four-way valve connected to the source and to the cylinder for selective reciprocation of the ram in the cylinder; a by-pass valve connected to the source in parallel with said four-way valve to control the fluid supply available to the four-way valve; a pilot valve connected to the by-pass valve for operating the by-pass valve; a ltime delay relay valve coupled to the four-way valve; another pilot valve coupled to the time delay valve; and a single actuator for simultaneously actuating both pilot valves a predetermined distance prior to the end of the stroke of the ram in either direction, whereby the by-pass pilot valve will act immediately to commence opening the by-pass valve, but the opening of the four-way valve will be delayed due to the action of the time delay valve.

6. A hydraulic pumping unit comprising: a fluid reservoir; a power driven pump adapted to receive fluid from the reservoir; a hydraulically operated four-way valve connected to the pump output and to the reservoir; a two-way actuating cylinder and ram; cylinder lines connecting opposite ends of the cylinder to the four-way valve for selective reciprocation of the ram; Va hydraulically operated by-pass'valve connected between the pump output and the reservoir; a primary four-way pilot valve having pressure and exhaust connections to the pump cutput and the reservoir; a time delay valve coupled to the primary pilot valve and coupled to the four-way valve for actuation of the four-way valve and having adjustments for regulating delay time; a secondary four-Way pilot valve having pressure and exhaust connections to the cylinder lines and connections to the by-pass valve, each of which includes a meter valve, for operation'of the by-pass valve; and a single actuator for simultaneously operating both pilot valves prior to the end of the stroke of the actuating ram, whereby the by-pass valve will be gradually opened, at a rate dependent upon the setting Vof the Vmeter valve, to effect a deceleration ofthe actuating ram, after which thefour-way valve will be operated to effect reversal of the actuating ram, following which the four-way valve will supply fluid in opposite sense to the secondary pilot valve to elect gradual closure of the by-pass valve at a rate dependent upon the 12 setting of the other meter Avalveto produce acceleration upon beginning of the next stroke.

7. In a hydraulic pumping unit employing an accumulator and a hydraulic actuating cylinder ram having a possible stroke in excess of a pump to be actuated, a control circuit for the gas pressure of the accumulator so as to eiect a constant predetermined stroke of the actuating ram comprising: a stroke-control valve whose spool is normally urged in one direction; a drive rod contacted by the actuating ram to return the spool toward a normal position upon each complete cycle of the actuating ram; a power operated make-up pump adapted to deliver gas under pressure to the accumulator; a control circuit for the pump adapted to be operated by movement of the spool past a normal lower position; and a blowdown valve for the accumulator adapted to be operated by the spool when it moves beyond its normal upper position.

8. A hydraulic pumping unit comprising: a reservoir; a constant-volume, power driven pump adapted to receive liquid from the reservoir; a four-way valve; a two-way cylinder connected to the four-way valve and having an actuating ram mounted therein for selective reciprocation; an actuator for the four-way valve operative to reverse the valve at the ends of the stroke of the actuating ram; an accumulator for assisting the pump on the pumping stroke; a stroke-control valve whose spool is urged in one direction by pressure from the pump; a drive rod contacted by the actuating ram to drive the spool lin the opposite direction at the end of each cycle of the actuating ram; a make-up pump coupled to the accumulator to deliver gas under pressure thereto; a blowdown valve connected to the accumulator to relieve gas pressure therein; a valve actuated by the stroke-control valve and responsive to the valve spool when driven past its normal position for actuating the pump; and an actuator coupled to the spool for actuating the blowdown valve responsive to the spool rising above its normal limit in response to pressure fluid.

9. A hydraulic pumping unit as defined in claim 8 wherein the make-up pump is hydraulically actuated and is connected to cylinder lines extending from the four-way valve to the cylinder, and wherein the stroke-control valve controls a three-way valve in one ofthe connections to the cylinder lines so as to selectively operate the make-up pump.

PAUL E. NOLL. T. DWIGHT ALLER.

REFERENCES CITED n The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,619,475 Hubbard Mar. 1, 1927 1,910,766 Hobson May 23, 1933 1,978,346 Ernst et al. Oct. 23, 1934 2,044,777 Erling June 23, 1936 2,051,052 Morgan Aug. 18, 1936 2,160,217 Kingsbury May 30, 1939 2,192,778 Stacy Mar. 5, 1940 2,347,302 Twyman et al. Apr. 25, 1944 Certificate of Correction Patent No. 2,57 2,748 October 23, 1951 PAUL E. NOLL ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 6, line 30, for clutch read circuit;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oiice.

Signed and sealed this 19th day of February, A. D. 1952.

THOMAS F. MURPHY,

Assistant Gommian'oner of Patents.

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