US2770197A

US2770197A - Hydraulically actuated pump

Info

Publication number: US2770197A
Application number: US393330A
Authority: US
Inventors: Roy H Deitrickson
Original assignee: Nat Supply Co
Current assignee: National Supply Co
Priority date: 1953-11-20
Filing date: 1953-11-20
Publication date: 1956-11-13
Anticipated expiration: 1973-11-13

Description

Nov. 13, 1956 Filed NOV. 20, 1953 R. H. DEITRICKSON 2,770,197

HYDRAULICALLY ACTUATED PUMP 4 Sheets-Sheet 1 Roy H. De/fric/rson 1956 R. H. DEITRICKSON HYDRAULICALLY ACTUATED PUMP 4 Sheets-Sheet 2 Filed Nov. 20, 1953 12621 66 0 DOLI OF HYDRAULICALLY ACEUATED PUMP Roy H. Deitrickson, Toledo, Ghio, assignor to The National Supply Company, Pittsburgh, Pa, a eorporation of Pennsylvania Application November 2%, 1953, Seriai No. 393,339

7 Claims. (Ci. lti345) This invention relates to hydraulically actuated pumps and, more particularly, to control apparatus for such a pump.

A hydraulically actuated pump of the type with which the invention is concerned comprises a generally vertically extending pumping cylinder or jack and a vertically reciprocable piston which is connected to the upper end of a sucker rod string extending down the well tubing to the production zone where the pump is located. The bydraulic system for reciprocating the piston in the cylinder comprises a working fluid pump and a counterbalancing pressure tank. The working fluid pump is connected in series between the counterbalancing tank and the pumping cylinder. The counterbalancing pressure tank functions to store energy during the down-stroke of the piston and to apply the stored energy through the working fluid pump during the up-stroke of the piston.

The average pressure to be maintained within the counterbalancing tank is determined by the work to be performed according to the following equation:

P 7-\ in which Pr is the unit pressure exerted on the piston by the weight of the sucker rod string, PS is the similar unit pressure exerted by the static head of production fluid in the column and PC is the average unit pressure which must be maintained in the counterbalancing tank.

Thus, if, for example, the weight of the sucker rod string is such that it creates a 200 p. s. i. pressure on the fluid beneath the piston and the weight of the column of production fluid creates a similar pressure of 400 p. s. i. then the average pressure to be maintained in the counterbalancing tank.

During an up-stroke of the pumping piston the counterbalancing tank supplies 400 p. s. i. to the input side of the pump and since the load to be lifted requires a pressure of 600 p. s. i., the pump supplies the additional 200 p. s. i. On the down-stroke the fluid circuit is reversed. The weight of the sucker rod string supplies 200 p. s. i.- to the input side of the pump and the pump again must supply' 200 p. s. i. in order to return the working fluid to .the counterbalancing tank which is maintained at the average pressure of 400 p. i. in order to store the energy for ap piication during the next up-stroke.

In normal operation of such ahydraulic pumping" apparatus, the pump operates under the same load during both the up stroke and the down stroke and a minimum number of controls are required to reverse the direction of the flow of the fluid from the counterbalancing tank through the pump to the working cylinder on the upstroke and from the cylinder through the pump to the counter balancing'tank on the down stroke; to'maintain a proper level of working fluid in the counterbalancing-tank; to maintain a constant average air pressure within the counterbalancing tank; and to properly recirculate the working fluid so that it can be cleaned, cooled and otherwise treated.

However, when gas is encountered in the production zone it may enter the production fluid pump in suflicient quantity to reduce the load on the working fluid pump. The pump engine then has a tendency to race which is harmful to the engine and the pump and may evendamage parts of the driving equipment and controls. The presence of this amount of gas in the well during an up stroke reduces the load on the engine by either displacing the heavier production fluid in the column or by exerting pressure upwardly against the column of production fluid in the well. The pumping jack piston then has a lighter load to lift which reduces the load on the working fluid pump and its driving engine. During the down stroke, if this amount of gas is present in the well, the weight of the production fluid column on top of the traveling valve holds the traveling valve closed and, therefore, the pressure on the fluid beneath the jack piston created by the weight of the sucker rod string has added to it the pressure created by the weight of the column of production fluid. Since the pressure beneath the piston is delivered to the input side of the working fluid pump during a down stroke, and since the sum of the pressures delivered to the input side of the pump and the pressure added by the pump need only be equal to the pressure maintained within the counter-balancing tank, the load on the working fluid pump is substantially reduced.

it is, therefore, the principal object of this invention to provide means in the hydraulic circuit of such a working fluid pump to properly modify the hydraulic circuit of the pump in order to compensate for gassing conditions within the well.

It is another object of this invention to provide hydraulic sensing means in the circuit of a hydraulic apparatus for actuating a working piston, such as a pumping jack, which is responsive to variations in the work to be performed by the working" piston and which correspondingly modifies the input pressure to the pump through which the working fluid is passed.

It is yet another object of this invention to provide hydraulic sensing means for sensing a reduction in the work to be performed by the pump for hydraulic system and to compensatingly decrease the input pressure to the pump inorder that the load on the pump may not'change as a result of changes in the work to be performed by the system.

It is yet another object of this invention to provide auxiliary hydraulically actuated valve means for restricting the input or suction line to a hydraulic pump in accordance with reductions in the pressure required to be delivered at the output side of the pump.

Yet another object of this invention is to provide a variable orifice for the input side of a hydraulic pump which is varied in response to the pressure necessary at the output side of the pump by the balance of pressure between the input and output sides of the pump.

Still another object of this invention is to provide an automatic control means to prevent rapid and wide varia tions in the speed of the pump driving engine by controlling the load on the engine, the load control being in the form of a device to maintain a relatively constant pressure differential across thepump in spite of variations in scale, of a surface hydraulic pumping apparatus embodying the invention.

Fig. 2 is a schematic circuit diagram of portions of the apparatus, hydraulic circuit, and controls for the operation and control of a pump embodying the invention.

Fig. 3 is a continuation of the diagram of Fig. 2 and particularly .illustrating means for controlling the fluid level and air pressure in a counterbalancing tank and the starting and stopping of a hydraulic apparatus embodying the invention; the left side of Fig. 3 being connected to the right side of Fig. 2.

Fig. 4 is a vertical sectional view, on an enlarged scale, of valve means constituting a part of the structure for carrying out the instant invention.

Fig. 5 is a vertical sectional view also on an enlarged scale of a hydraulic pressure sensing valve mechanism for actuating a portion of the structure shown in Fig. 4 for controlling pressures affecting the operation of the main pump of the hydraulic system.

Fig. 6 is a vertical sectional view taken substantially on the line 6-6 of Fig. 5.

A hydraulic apparatus embodying the invention is erected near the top of a well tubing which extends downwardly through a well casing (not shown) leading from the surface of the ground to the production zone.

The apparatus comprises a counterbalancing tank which may be erected upon legs 31 located adjacent the tubing 25 and mounted upon a general framework 32.

A main driving engine 33 has a clutch (not shown) that is connected through a drive shaft extending along l a shaft tunnel 34 to a drive shaft 76 (Fig. 2) of a main pump 40. The pump is connected through suitable valving to a counterbalancing tank line 41 and through the valving to a line 42 to a pumping jack 43. The pumping jack 43 contains a vertically reciprocable pumping jack piston 44 which is connected to the upper end of a sucker rod 45 string extending down into the tubing 25 and is thus connected through the string to a pump plunger at the well production zone in the usual manner.

The pumping jack 43 is erected upon suitable legs 46 and connected into the hydraulic system by a line 47 connected to its upper end and a stroke control line 48 communicating with upper and lower

stroke selector valves

49 and 49a. The stroke selector valves form no part of the present invention and are not shown or described in detail.

Other pipes and lines indicated in Fig. 1 and bearing reference numbers of a higher order, as well as the connections and interrelationships of the parts already described, will be set forth in a description of the operation of an apparatus embodying the invention and no structural description of these parts will be made except in connection with their operation.

OPERATION In describing the operation of the surface hydraulic apparatus embodying the invention it will be assumed that the apparatus has been at rest for a sufficient period of time for the pressures in the various hydraulic lines to have dropped otf and for the pressure in the counterbalancing tank with which the apparatus is equipped to have fallen below that normally maintained during the operation of the device.

Start In order to start the apparatus embodying the invention and because of interlocked controls later to be described, it is necessary to first disestablish a cutout circuit leading to the magneto of the engine which powers the apparatus. The purpose and operation of this cutout circuit will be described later. The cutout circuit is disabled by opening an engine start switch 50 (Fig. 2). Depressing the engine start switch 50 opens a circuit between ground and the engine magneto (not shown) so that the engine can be started in the conventional manner. After the engine CJI has been started and is operating at a satisfactory speed the operator of the apparatus swings a control valve generally indicated at 51 (Fig. 3) to the Start" position indicated therein in broken lines. The control valve 51 comprises a manually operable handle 52, a valve housing 53 (shown in exploded view in Fig. 3) and a valve rotor having two control sections 54 and 55. When the handle 52 is swung to start position the control section 55 is rotated in a counterclockwise direction (Fig. 3) a distance sufiicient to place a pipe 56 in communication with a pipe 57. The pipe 56 is connected directly to a bottom pipe 58 on the counterbalancing tank 30. The fluid in the tank 30 is fed through the

pipes

58 and 56 to the valve 51 and then through the pipe 57 and a check valve 59 to a line 60 which leads to a cylinder 61 in a safety shut down pilot Valve generally indicated at 62.

The safety shut down pilot valve 62 has a large diameter piston 63 and an opposed small diameter piston 64 which are connected by a stem 65 through which there extends an axial bore 66. The bore 66 leads from the right or outside end of the piston 64 to the right or inside end of the piston 63. The pressure from the counterbalancing tank 30 through the lines set forth above forces the piston 63, stem 65 and piston 64 to the right compressing a piston return spring 67.

Movement of the valve stem 65 to the right moves a smaller diameter piston 64 away from a shoulder 68 intermediate a pair of annular grooves 69 and 70 in the body of the valve 62 and places a pipe 71 in communication with a second pipe or line 72. The pipe 71 is connected through a restriction 73 to the line 60 and, therefore, fluid under pressure from the counterbalancing tank 30 flows into the line 72 leading to an engine clutch control cylinder 74 Where it forces an engine clutch control piston 75 to the right to engage a clutch between the engine and a drive shaft 76 (Fig. 2) for the main pump 40 and a scavenging pump 77.

At the same time fluid from the counterbalancing tank 30 is led through a continuation of the pipe 72 to a shut 01f valve cylinder 78 (Fig. 3) and thrusts a shut off valve piston 79 to the right opening a main shut olf valve 80 on the bottom of the counterbalancing tank 31) and connecting the tank 30 to the main pump line 41.

The pockets back of the smaller piston 64 in the safety shut down pilot valve 62, the piston 75 of the engine clutch control cylinder 74 and the piston 79 of the shut off valve 78 are all connected to a line 81 leading to the control valve 51 and connected through a restriction 82 to the pipe 56 and the pipe '58 to the counterbalancing tank 30. When the control section 55 was rotated in a counterclockwise direction to connect the pipes 56 and '57 as described above the pipe 81 was simultaneously connected to a pipe 83 leading to a sump line 84. The sump line' '84 communicates directly and freely with a main oil sump 85 (.Fig. 2).

Because of the restriction 82 in the line 81, the pressure in the line 81 is lower than the pressure in the line 56 and, therefore, the pressure in the three pockets back of the

pistons

64, 75 and 79 is lower than the pressure on their operating faces. in addition, by the connections just described the line 8-1 is opened to the sump. Therefore, even though the line 81 is connected through the restriction 82 to the line '56 the pressure in the line 81 is substantially lower than the pressure in the line '56 and the three pistons described above can move to the right.

By reason of the clutching in of the drive shaft 76, the main pump 40 and scavenging pump 77 are now driven by the main engine. The scavenging pump 77 is a rotary .pump shown schematically in Fig. 2 and pumps fluid from the sump 85 through check valve 86 and a scavenging pump intake line 87 (Fig. 2) to the pump 77 and from the pump 77 through a scavenging pump output line 88. The line 88 has a branch 89 (Fig. 2) which is connected directly to a junction of the two

lines

71 and 60 indicated by the reference number 90 in Fig. 3.

As soon as the scavenging pump reaches its pressure which is so selected as to be greater than the pressure in the interior of the counterbalancing tank 30, operating fluid starts to flow from the sump 85 and through the scavenging pump 77 to the line 71 and through the annular grooves 70 and 69 to the line 72 and to the engine clutch control cylinder 74 and the shut off valve 78. Fluid from scavenging pump also kows through the branch of the line 60 to the cylinder 61 and takes over the job of holding the safety shut down pilot valve 62, engine clutch control 74 and shut off valve 78 in the positions shown in Fig. 3.

The operator can then return the handle 52 to the center position shown in Fig. 3, in which position none of the

line

56, 57, S1 or 83 is connected to any of the other lines in that group. Upon return of the handle 52 to the run-off, or central position, and the disconnection of the line 81 from the sump line 8384, fluid from the counterbalancing tank 30 builds up counterbalancing tank pressure in the line 81 and on the back sides of the pistons in the valve 62, clutch control cylinder 74 and shut off valve cylinder 78 even though the restriction 82 is interposed therebetween. However, because the pressure on the output side of the scavenging pump and thus into the line 89 is higher than the pressure in the tank 30 the three pistons in these three structures remain in their operating positions.

U pstroke With the starting controls returned to their run position and the shut oif valve and engine declutching pistons held in operative position by the scavenging pump pressure, the apparatus enters its cycle of operations. The main line 41 from the counterbalancing tank 30 leads to the input side of the main pump 40. The main pump 40 is a rotary screw type pump having inter-meshed pumping screws 91 which pump fluid from the outer sides of the pump 40 toward the center of the pump 40 and out of the pump 40 through an output manifold 92. During the upstroke the output manifold 92 is connected by means of a reversing valve generally indicated at 93 to the main pump jack line '42. The line '42 is connected to the lower end of the vertically extending pumping jack cylinder 43. The line 42 is connected into the pumping jack cylinder 43 below the lowest point of travel of the pumping jack piston 44 so that ingress of fluid from the pump 40 forces the piston 44 upwardly lifting the rod '45 and the column of production fluid from the bottom of the well to the production fluid takeofi manifold (not shown).

In operating apparatus of the type embodying the instant invention the power to be exerted by the main pump 40 and the pressure to be maintained and exerted within the counterbalancing tank 30 are calculated according to the equation set forth above in the introduction to this specification.

Using the figures set forth earlier, during a normal upstroke of the device it is necessary to counter-balance the total pressure created by the

rod

45, 200 p. s. i. and that created by the colume of production flund, 400 p. s. i., or a total of 600 p. s. i. To accomplish this lifting there is available to the apparatus the 400 p. s. i. pressure within the counterbalancing tank 30 and pressure provided by the main pump 40, in this case 200 p. s. i. The two pressures are added in the pump '40 where the input to the pump from the line 41 is at the pressure of the tank 30 and wherein the pump 40 adds 200 p. s. i. to the input pressure of 400 p. s. i. to provide the 600 p. s. i. necessary.

The application of the 600 p. s. i. pressure thus accumulated to the pumping jack 43 beneath the pumping jack piston 44 moves the pumping jack piston 44. upwardly. As the pumping jack piston 44 is moved upwardly the fluid pumped thereinto lowers the level of the fluid in the counterbalancing tank 30. In order to maintain the air pressure in the tank 30 within operating limits, it is, of course, necessary to pump air into the tank 30 from time to time. A compressor (not shown) is connected to the tank I30 to pump lair thereinto under the control of an air pressure sensing and control means generally indicated at in Fig. 3, the operation of which will be described below. With the inflow of air into the counterbalancing tank 30 substantial quantities of condensed moisture are carried into the tank 30. The moisture may combine with substances in the working fluid to produce corrosive materials. It is customary in installations of this type, therefore, to recirculate the Working fluid into and out of the counterbalancing tank 30 and the sump '8'5 and to feed the fluid during its recirculation through filters and heat exchangers and to feed the fluid back into the counterbalancing tank 30 by spraying it onto the interior walls of the tank 30 to wash them with the anti-corrosives contained in the working fluid.

In the instant apparatus this recirculation is accomplished by the scavenging pump 77. The scavenging pump output line 88 (from which the branch line 89 leads to the starting apparatus described above) is connected through a filter 96 (Fig. 3) and heat exchanger 97 to a variable spray nozzle 93 mounted at the top center of the counterbalancing tank 30. The nozzle 98 has a piston-like plunger 99 connected by a rod 100 to a disk 101 which extends across the open end of the spray housing 98 inside the tank 30. The end of the housing 98 is coned and the lip of the disk 101 beveled so as to create an outwardly and upwardly inclined annular orifice when the disk 101 is moved downwardly varying distances away from the end of the spray nozzle The operation of the spray nozzle and its control by varying pressures within the counterbalancing tank 30 is fully disclosed in and constitutes the subject matter of my copending application Serial No. 354,168 filed May 11, 1953 now abandoned and will not, therefore, be described in detail in the instant application. The size of the annular orifice formed between the disk 101 and the end of the spray nozzle 93 varies according to varying pressure within the counterbalancing tank 30 since the pressure in the scavenging pump output line 88 remains constant and higher than the maximum pressure within the tank 30. Thus the area of impingement of the sprayed fluid on the inner wall of the tank 30 is constantly varied to insure that the fluid washes over the entire surface of the tank and the size of the spray orifice is constantly varied thus varying the velocity of the fluid therethrough to insure that it remains clean and open. The volume of fluid which is pumped into the counterbalancing tank through the spray'98 is controlled by the maximum output of the scavenging pump 77 and may be reduced or increased by the action of fluid level control means generally indicated at 102 in Fig. 3 and to be described below.

T 0p reversal Under normal conditions within the well and with respect to air pressure and fluid level, as touched upon above and to be described in detail below, the pump 40 continues to force operating fluid into the pumping jack 43 raising the piston 44 and rod 45 upwardly until the piston 44 passes one of a series of stroke length control ports 103 near the topof the pump jack 44- and' connected to the upper stroke selector valve 49. The valve 49 may be selectively connected to any of its ports 103 so that when the piston 4 passes the connected one of the ports, the interior of the pumping jack 43 is connected through a check valve 106 with the line 48 leading to thefleft:

forcing a large piston 107 toward. the right (Fig. 2').v

The piston 107 is on the left end of a spool valve stem 108 at the right end of which there is located a smaller diameter piston 109. A pocket 110 in the pilot valve 106 back of the piston 107 is connected through a line 111 to the sump line 84 and thus no resistance to the movement of the piston 107 to the right is afforded by fluid in the pocket 110. A pocket 112 at the right or beyond the small piston 109 is connected by a line 113 to the main counterbalancing tank line 41 and, therefore, the pressure of the counterbalancing tank resists the movement of the spool valve structure 108 to the right. This prevents the spool valve 108 from being sharply driven to the right when pressure is applied to the piston 107 as outlined above.

When the spool 108 moves to the right a portion 114 of small diameter spans a groove 115 and an adjacent groove 116. This places a branch 113:: of the line 113 in communication with a line 117 which leads to a lefthand pocket 118 in the reversing valve 93 so that the valve 93 is subjected to counterbalancing pressure tending to move it to the right, in a direction to shift the main pump output to the counterbalancing tank as described below.

The reversing valve 93 slides on a pair of opposed, spaced, coaxial stems 119 and 120. The stems 119 and 120 extend into the ends of a sleeve 121 constituting the movable body of the reversing valve 03. The ends of the sleeve 121 fit over the stems 119 and 120 and a cross web 122 in the sleeve 121 separates the pockets thus formed from each other, the pocket 118 being located at the left side of the web 122 and a similar pocket 123 being located at the right side of the web 122.

The sleeve 1.21 has two axially spaced,

annular shoulders

124 and 125 which are the valving surfaces of the reversing valve 93 and which cooperate with inwardly turned pairs of

annular lips

126 and 127.

With the reversing sleeve 121 in its left position as shown in Fig. 2, the shoulder 124 is engaged with the lefthand one of the lips 126 and the shoulder 125 with the righthand one of the lips 127. The outlet manifold 92 of the pump 40 is thus connected directly to the pumping jack line 42 through the annular passageway located between the two

shoulders

124 and 125. At the same time the intake side of the pump 40 is connected through an annular orifice 128 to the main line 41 from the counterbalancing tank 30.

When the line 113 is connected through the grooves 115 and 116 to the line 117 by movement of the pilot valve stem 108 to the right as described above, and fluid from the counterbalancing tank is fed into the pocket 118 at the left side of the web 122 of the reversing valve 93, the sleeve 121 is slid to the right. At. the same time the pocket 123 at the right of the web 122 is connected through its line 129 and an annular port 130 in the pilot valve 106 to an annular port 131 and through a bleeder valve 132 to the sump connecting line 111 and the sump line 84 to the sump 85.

The reversing valve sleeve 121 is thus actuated by counterbalancing tank pressure on one side of the web 122 against sump pressure on the other side of the web 122. The pocket 123 is vented to the sump through the bleeder valve 132 which inserts resistance in the connection to slow the reversing valve sleeve 121 in its movement. A further resistance to the movement of the reversing valve sleeve 121 to the right as it approaches the end of its travel is provided by a dash pot" formed by an enlargement 133 (Fig. 4) on the stem 120 co-operating with an annular space 133a around the stem 120 and consisting in an enlarged portion at the end of the bore of the sleeve 121. A quantity of fluid is trapped between the surfaces of the enlarged bore 133a and the enlargement 133 which must escape through the slight clearance between the two concentric, overlapping, cylindrical portions. The sleeve 121 is stopped in its movement to the right by the engagement of its end with a shoulder 133!) 8 at the base of the righthand stem 120 beyond the en larged portion 133.

When the reversing valve 93 has thus been shifted, the main pipe 42 from the pumping jack 43 to the pump 40 is connected through an annular orifice 134 to the input side of the pump 40 and the output manifold 92 of the pump 40 is connected through the annular space between the

shoulders

124 and 125 to the main line 41 leading to g the counterbalancing tank 30.

Downstroke During the downstroke of the surface hydraulic apparatus embodying the invention the weight of the sucker rod is relied upon to pull itself and the pumping jack piston 44 downwardly. However, because the Working fluid beneath the piston 44 must be returned to the counterbalancing tank 30 it is necessary for the pump to supply suflicien't pressure to be added to the pressure created by the weight of the sucker rod 45 in order to overcome the pressure existing within the counterbalancing tank 30. Using the figures set forth above in the earlier discussion of pressures, if the sucker rod creates 200 p. s. i. and the desired counterbalancing tank pressure is 400 p. s. i., it is necessary for the pump to supply the additional 200 p. s. i. With the connections established as discussed above under the heading Top Reversal the fluid beneath the pumping jack piston 44 is led through the line 42 to the input or low pressure side of the pump 40. The output manifold 92 of the pump 40 is connected to the main line 41 leading to the bottom of the counterbalancing tank 30. Thus, under normal operations the pump has an input pressure of, say, 200 p. s. i., and increases the pressure on the fluid 200 p. s. i. to force the fluid into the counterbalancing tank 30.

As the pumping jack piston 44 moves downwardly the pump 40 forces the fluid into the counterbalancing tank 30 raising its level. The inflow of fluid into the tank 30 may increase the pressure on the air in the tank 30 and this again is controlled by the air control apparatus gen erally indicated at in Fig. 3 and to be described below. If, because of the constant recirculation of the fluid by the scavenging pump 77 the quantity of fiuid in the counterbalancing tank 30 is too great so that upon replacement therein of the fluid pumped from the jack 43, the level of fluid in the counterbalancing tank reaches a maximum desirable level, the fluid level control means generally indicated at 102 is actuated to prevent the adding of more fluid to the tank 30. Particular operation of this apparatus also will be described below.

Bottom reversal As the piston 44 reaches the bottom of the jack 43 it passes one of the ports 135 of the bottom stroke selector valve 49a (Fig. 2) and the space in the jack 43 above the piston 44 is placed in communication through the valve 49a and a check valve 136 with a branch of the line 48 leading to the left side of the pilot valve 106. At

the time of the top reversal described above the spool valve 108 and the

pistons

107 and 109 of the pilot valve 106 were thrust to the right and, because of the check valve 104 the Working fluid admitted into the line 48 was maintained at its high pressure to hold these parts of the pilot valve 106 at the right. Similarly, of course, the working fluid beneath the jack piston 44 had been present in the control ports 135 of the valve 49a and beneath the ball check valve 136 so that the same pressure existed throughout the system comprising the check valve 104, check valve 136 and line 48 to the pilot valve 106 As soon as the piston 44 passes the port 135, however, the pressure beneath the check valve 136 is relieved to the vented space above the piston 44 and the pocket at the left side of the large piston 107 of the pilot valve 106 is also relieved. Since counterbalancing tank pressure is continuously applied through the line 113 to the pocket 112, the spool 108 is thrust to the left, exhausting the 9 fluid from the pocket back of the piston 107 and through the line 48 into the pumping jack 43 above the piston 44. Such fluid is subsequently dlscharged from the jack 43 through the vent line 47 to the sump 85 along with fluid which leaks past the piston 44, when the piston 44 reaches the top of its next upstroke.

When the pilot valve 106 is moved to the left its component parts are restored to the position shown in Fig. 2 and the line 113 is connected through its branch 113a to the groove 116 and the port 130 to the line 129 and the right-hand pocket 123 of the reversing valve 93. Application of the counterbalancing tank pressure into the pocket 123 thrusts the reversing valve sleeve 121 to the left (Fig. 4). As in the case of its earlier described movement to the right (see above) the sleeve 121 is slowed by the metered escape of oil from the pocket 113 and by the dash pot eflect of an enlargement 137 on the stem 119 and a mating enlarged end portion 137a of the bore in the sleeve 121. The movement of the sleeve 121 to the left is finally stopped in the position shown in the drawings with the end of the sleeve 121 against a stop shoulder 1371) at the base of the stem 119. This shift of the sleeve 121 reconnects the input side of the pump 40 to the line 41 from the counterbalancing tank and the output manifold 92 of the pump 40 to the main line 42 leading to the pumping jack 43. With the parts restored to the position shown in the drawing the apparatus again enters an upstroke.

Fluid level control As mentioned briefly above, because of the recirculation of the fluid into and out of the counterbalancing tank 30, both by the surging in the main line 41 upon change of direction of movement of th Piston 44 and by the scavenging pump 77, it is necessary to provide means to control the maximum level of the fluid in the counterbalancing tank 31 This means is generally indicated at 1112 in Fig. 3.

In detail, the fluid level control apparatus comprises a line 138 connected to the tank 30 at the maximum fluid level. The line 138 is led downwardly for a considerable distance to provide for a head of fluid in the line 138 and then connected into a fluid level pilot valve housing 139 at a point beneath an imperforate diaphragm 140 extending across the housing 139,. The diaphragm 140 mounts a diaphragm plunger 141 which extends downwardly through a valve sump 142 and cooperates with a cone seat 143 to form a valve at the upper end of a branched line 144. The space beneath the diaphragm 140 is connected to the sump 142 by a passageway 145. The space within the housing 139 above the 'diaphragm 141' is connected through a line 146 to a vertically extending air line 147 which is connected into the counterbalancing tank 30 at a point well above the maximum fluid level. A coil spring 148 extends between the top of the housing 139 and the upper surface of the diaphragm 140 thrusting the diaphragm 14% and plunger 141 downwardly into seating engagement with the cone seat 143.

By connecting the line 147 above the diaphragm 140, air pressure in the tank is applied to both sides of the diaphragm at all times.

The spring 148 is so selected that its force is suflicient to hold the plunger 141 in place until the fluid in the counterbalancing tank 30 fills the vertically extending line 138. When this occurs the head of fluid in the line 133 overcomes the spring 148 and lifts the diaphragm 141) to open the valve formed by the plunger 141 and cone seat 143. Fluid from the tank line 138 then flows through the sump 142 and the branched line 144, one arm 149 of which feeds through a bleeder valve 150 to the sump line 84. The other branch 144:: of the line 144 is connected to a fluid dump valve 151 beneath a piston 152 which has a stem 1 53 acting as a valve between a 10 scavenger pump input line 154 and a branch line 155 to the main counterbalancing tank line 41.

When the level of fluid in the counterbalancing tank 30 reaches the maximum desired level and the head of fluid in the vertical line 138 opens the fluid pilot valve 102, the fluid in the tank 30 and in the line 138 flows downwardly and into the branched line 144 under the counterbalancing tank pressure. This high pressure fluid opens the dump valve 151 and establishes a circuit from the main counterbalancing tank line 41 directly to the scavenger pump input line 154. As long as a suflicient head of fluid remains in the line 138 to hold the pilot valve 139 open the dump valve remains open under tank pressure transmitted thereby and working fluid is withdrawn from the bottom of the counterbalancing tank 30 directly into the scavenging pump 77 and recirculated back into the tank 30] This action allows the sump check valve 86 (Fig. 2) to close and no additional fluid is added to the tank 30 during this direct recinculation cycle.

Because additional fluid is not pumped from the sump to the tank 30, the level of the fluid within the tank 30 finally drops below the maximum desired level. The head of fluid in the line 138 gradually lowers, being drained away through the bleeder valve 150 to the sump line 84, until the fluid pressure on the underside of the diaphragm 1413 becomes less than the pressure of the spring 148 and the diaphragm 140 moves downwardly closing the pilot valve formed by the plunger 141 and the cone seat 143. This cuts off the dump valve 151 from the tank pressure and as the fluid within the

lines

144a and 149 bleeds away through the bleeder valve 150, the dump valve piston 152 is thrust downwardly by a coil spring 156 to close the dump valve, restoring the apparatus to the position indicated in Fig. 3 and re-establishing the flow of fluid from the sump through the scavenging pump 77 to the counterbalancing tank 30.

Air pressure control apparatus As has been briefly mentioned above an air compressor (not shown) is connected to the tank 30 to provide the air pressure necessary to build up the required, for example, 400 pounds pressure in the tank 30. Because of the variations in the quantity of fluid in the tank 30 resulting from the resurgence due to the pumping of the piston up and down in the jack 43 and in order to provide a control over the operation of the air compressor which would otherwise continue to increase the pressure in the tank 30, air pressure control means are provided.

The air pressure control means 95 comprises among other parts the line 147 already mentioned which is connected by the line 146 to the fluid level pilot valve housing 139. The line 147 also is connected through a check valve 157 to a control valve line 158 and to a line 159 through a bleeder valve 160 to the sump line 84. The line 158 leads to an air chamber 161 and two parallel spring loaded

valves

162 and 163. During the fluid return portion of a pump cycle, as air pressure builds up in the tank 30, it opens the check valve 157 and charges the air chamber 161. The air chamber 161 thus has a pressure which is equal to the maximum pressure within the tank 30 at any time. When the pressure within the air chamber 161 becomes higher than the maximum pressure which is desired to be maintained in the tank 30, it opens the air control valve 162 placing the air chamber 161 and line 158 in communication with a line 164 to control means for the air compressor. Such control means may be either a pneumatically actuated clutch or a pneumatically actuated unloading valve on the air compressor or other conventional control means so that no further air is pumped into the tank 30 as long as the valve 162 is open.

When the air compressor has stopped and until the maximum air pressure within the tank 30 and thus in the air chamber 161 drops to the desired point, the valve 11 162 stays open, holding the air compressor in inoperative condition. During this time, of course, air bleeds through the bleeder valve 160 to the sump line 84 and the pressure within the air chamber 161 is decreased under control of the bleeder valve 160, reducing the pressure acting against the valve 162.

As soon as the pressure within the air chamber 161 bleeds down below the maximum desired level, and providing that the maximum pressure within the tank 30 does not go above such level (which would, of course, recharge the chamber 161), the control valve 162 closes and the air compressor control is de-energized so that the compressor once again pumps air into the tank 30.

Because many installations of surface hydraulic equipment for wells are located in hot, arid climates, provision must be made for an extra control to react to pressure in the tank 30 in excess of that normally to be expected and which is controlled by the air pressure control means just described. For example, if high temperatures causes the pressure within the tank to climb even after the compressor is stopped, the air in the line 158 and air chamber 161 also is above normal. Since the valve 162 is already open, the higher pressure opens the second control valve 163 which is set to open at a slightly higher pressure than that at which the first control valve 162 opens.

When the second control valve 163 opens, the line 158 is placed in communication with a line 165 leading to a space beneath a piston 166 of an air dump valve 167. This displaces the piston 166 withdrawing its stern 168 and placing an auxiliary tank air line 169 in direct communication with a line 170 leading to the sump 85. Air is then bled directly from the tank to the sump, rapidly reducing the pressure within the tank 30.

Simultaneously, of course, the pressure within the air chamber 161 is bleeding through the bleeder valve 165). The bleeder valve 160 must be so adjusted that it allows the pressure within the chamber 161 to drop faster than the vent line 169 drops the pressure within the tank 31}. Otherwise the pressure in the air chamber 161 might continue to hold the dump valve 167 open and the compressor inoperative while all of the air in the counterbalancing tank 39 was vented through the dump valve 167. As soon as the pressure within the chamber 161 is lowered sufliciently to allow the control valve 163 to close, the dump valve 167 is closed by the action of a spring 171 and the dump line 169 disconnected from the sump.

Air continues to bleed from the air chamber 161 through the bleeder valve 160 until the pressure within the air control system lowers to a point that the air cornpressor is re-engaged; again providing that the maximum pressure in the counterbalancing tank 30 during the inflow of the fluid does not rise above the desired maximum.

Stop

When it is desired to stop the apparatus the operator swings the control lever 52 (Fig. 3) to the stop position which rotates the control sections 54 and 55 in a clockwise direction. The movement of the section 55 has no effect upon the connections of the line 56 57, .81 and 33 but movement of the control section 56 connects the line 6% to a branch line 172 leading to the Sump line 54. This connects the cylinder 61 of the pilot valve 62 to the sump. The tank fluid in the line 81 acts against the piston 6-4 thrusting the stem 65 to the left and inserts the body of the piston 64 across the annular groove 70. This cuts off the flow of scavenging pump output fluid through the line 71 and at the same time connects the line 72 through the annular groove 69 and an adjacent annular groove 173 to a line 174 which is connected to the main sump line 84. Connecting the line 72 to the sump line 84 removes the pressure from the left side of the engine clutch control piston 75 and the shut off piston '79 and counterbalancing tank pressure in the line 81 thrusts these two pistons to the left disconnecting the 12 engine from the main pump 40 and closing the counterbalancing tank shut off valve 78.

When the engine is disconnected from the pump drive shaft, pressure immediately falls throughout the entire system. If desired, the engine may be stopped by closing an engine stop switch 174 (Fig. 2) which shorts out the engine magneto.

Pressure and temperature cut-ofis in order to protect the hydraulic system from unforeseen injuries due to obstructions, to insure its cessation of operation in the event of a substantial leak and to stop its operation if temperatures in the pump, for example, reach a dangerous level, certain safety controls responsive to high and low pressure and to temperature are provided. A high temperature cutoff switch generally indicated at 175 comprises a Bourdon tube 176 connected by a line 177 to a temperature responsive element 178 located in the output manifold 92 of the pump 40. When the temperature in the output manifold 92 reaches too high a level, the Bourdon tube 176 responds, closing a pair of contacts 179 to the magneto shorting circuit and stopping the operation of the main engine 33 to stop the pump 40 and scavenging pump 77.

Similarly, a high pressure cutoff switch 180 has a Bourdon tube 181 that is connected by a line 182 to the output manifold 92 of the pump 40. In the event that the pressure in the output side of the pump is raised above a safe level, the Bourdon tube 181 straightens, closing a pair of contacts 183 and again shorting out the engine magneto, stopping the engine 33.

A low pressure cutoff gauge 184 is connected by a line 185 to the low pressure or input side :of the main pump 40. If the pressure on the input or low pressure side of the main pump 40 drops below a normal operating level, for example, by an obstruction in the input lines, a Bourdon tube 186 in the gauge 184 is relaxed and closes a normally open pair of contacts 187, again establishing the magneto shorting circuit.

The main pump 40 hasa relief generally indicated at 188 and interposed between the output manifold 92 of the pump 40 and a duct 189 to the input side of the pump 40.

The back side of the valve 188 is connected by a short line 190 to the low pressure duct 189 and normally sealed therefrom by the valve 188. The back side of the valve 188 also is connected through a line 191 to a manually operable valve 192 to the main sump line 84.

A high pressure bypass line 193 is connected between the high pressure line 182 and the line 191 above the valve 192. The line 193 has a restricted orifice 194. High pressure fluid thus exists on both sides of the valve 138 and a coil spring 195 is relied upon to hold the valve closed during operation.

When it is desired to dump fluid from the main pump 40, an operator opens the valve 192 and, because of the orifice 194, the pressure of fluid in the line 191 back of the dump valve 188 is reduced below that in the line 193 ahead of the orfiice 194. The pressure on the relief valve 188 exists at the output pressure of the pump in the manifold 92 and pressure on the back of the relief valve 188 is lowered by the drop across the orifice 194. Therefore, the high pressure in the manifold 92 thrusts the relief valve 188 to the left, balancing the pressure on the two sides of the pump 40.

Gassing conditions UP STROKE Gas in the bottom of the well during an up stroke of the piston 44 exerts pressure upwardly against the column of production fluid in the well. This, in effect, reduces the weight of the column of production fluid and thus reduces the pressure on the piston 44 normally created by the weight of the column of production fluid being lifted during the up stroke. Since the pressure on the piston 44 during an up stroke is the sum of the pres- 13 sure created by the weight of the rod 45 and the pressure created by the weight of the column of production fluid being lifted, this total pressure is reduced in proportion to the reduction in theweight 'of the column of production fluid, i. e., the upward pressure of the gas in the well.

Under normal operations the load of the rod 45 and column of production fluid is overcome by adding the pressure from the counterbalancing tank 30 to the pressure created by the main pump 40. Since it is desirable not to change the load on the main pump 40, i. e., not to change the pressure differential between the input and output sides of the pump 40, when gas in the well reduces the work to be performed, it is necessary to reduce the pressure applied to the input side of the pump, i. e., the pressure supplied by the counterbalancing tank 30 According to the invention the reduction in load caused by gas during an up stroke is sensed and employed to hydraulically shift valve mechanism which throttles the input orifice 128 between the counterbalancing tank line 41 and the input side of the pump 40. This mechanism operates as set forth below.

During the up stroke of the piston 44 the reversing valve sleeve 93 is at its left hand position (Figs. 2 and 4). Operating fluid is flowing in through the line 41 from the counterbalancing tank 30 and through the annular orifice 128 to the input manifold generally indicated at 196 in Fig. 4. If the conditions just described exist, the pressure in the line 41 from the counterbalancing tank is, in effect, higher than necessary and thus the difierential between the pressure in the input manifold 196 and the output manifold 92 of the pump is smaller than that which is desirable to maintain. The pressure in the input manifold 196 is sensed by an input pressure sensing line 197 which is connected to a cylinder 198 (see Fig. 5) of a counterbalancing valve generally indicated at 199. The line 197 leads into the cylinder 198 through a duct 200 at the left side of a main piston 201. The piston 201 is connected to a valve stem 202 extending through a block 203 in the center of the valve 199 and carrying a smaller diameter piston 204 at its right end. The piston 204 reciprocates in a cylinder 205 in the valve 199 and the right side of the cylinder 205 is connected by a duct 206 to a line 207. The line 207 (Fig. 2) is connected to a divided line 203, one arm 209 of which (see also Fig. 4) is permanently connected to the high pressure manifold 92 of the pump 40.

The line 208 also is connected into a pair of bleeder valves 210 one of which is connected to each of a pair of lines 211 (Fig. 4) and the lines 211 are connected by a common line 212 which leads to an annular port 213 (Fig. 5) in the valve 199.

The cylinder 198 in the valve 199 is connected through an annular port 214 to a line 215 (Fig. 2) to the sump line 111 and the main sump line 84 to the sump 85. A cross bore 216 (see also Fig. 5) in the valve stem 202 intersects an axial bore 217 in the stem 202 and leads to a radial bore 218 also in the stem 202. The radial bore 218 opens to a pocket 219 in the interior of the block 203.

Under normal conditions (where no gas is present in the well) the high pressure output manifold 92 of the pump 40 is connected through the

lines

209, 208 and 2&7 and the duct 206 to the cylinder 205 at the right side of the piston 204. This higher pressure fluid at the output side of the pump acting on the area of the end of the piston 204 exerts sutficient pressure to hold the piston 204, stem 202 and piston 201 at the left side of the counterbalancing valve 199 against the pressure of the input side of the pump at the left side of the piston 201 and in the duct 200 and line 197.

When, as explained above, the pressure differential between the two sides of the pump is reduced, the input pressure to the pump is great enough with respect to the output pressure of the pump so that input fluid at the 14 left of the piston 201 moves the piston 201, stem and piston 294 to the right (Fig.5). As soon as they stem 202 starts to move to the right a tapered portion 220 breaks the seal between the stern 202 and a land 221 at the left side of the annular port 213 and the line 212 is placed in communication through the port 213 and around the tapered section 220 with the port 214 and the line 215 to the sump.

The line 212 is connected commonly to the two lines 211. Each of the lines 211 leads into one of a pair of annular pockets 222 and 223 (Figs. 2 and 4). By thus connecting the

pockets

222 and 223 to the sump pressure, two throttling

sleeves

224 and 225 can be moved inwardly in a direction to restrict symmetrically the input passages of the pump and thus re-cstablish the desired pressure differential from input to output through the pump.

During the up stroke, the throttling sleeve 225 is operative and the following description will be restricted to that sleeve alone, the operation of sleeve 224 being subsequently described in connection with a downstroke.

The throttling sleeve 225 has a tubular section 226 which slides on an annular land 227 adjacent the edge of the annular input orifice 128. The throttling sleeve 225 also has an outwardly extending radial rim 228 and is exposed to input pressure through an annular passageway 229 extending around the reversing valve stem 120, on its rear face 230.

By venting the pocket 223 to the sump through the

lines

211, 212, the orifice 213 (see Fig. 5) around the taper 220, the port 214 and the line 215, the input pres sure of the pump is sufficient to slide thethrottling sleeve 225 to the left (Figs. 2 and 4) partially closing the annular orifice 128. Restricting the orifice 128 causes a pressure drop between the input line 41 from the counterbalaucing tank 30 and the input manifold 196 of the pump 40. This reduces the input pressure to the pump 40 making it necessary for the pump to add its 200 p. s. i. to build up suflicient pressure in its output manifold 92 to lift the load of the production fluid with gas underneath.

The extent of movement of the stem 202 (see Fig. 5) of the counterbalancing valve 199 is directly proportional to the reduction in the differential between the input or counterbalancing tank pressure to the pump 40 and the output or load lifting pressure of the pump 40. If the load on the jack piston 44 has been reduced to a greater extent the differential between the pressures on the two sides of the pump is smaller and the counter-- balancing valve stem 202 is correspondingly moved a greater distance to the right. The greater the distance the stern 202 is moved to the right the larger the annular orifice around the tapered portion 220 and through the land 221. The larger this annular orifice, the less re sistance there is to flow from the

pockets

222 and 223 to the sump and, consequently, the farther the throttling sleeve 225 is moved to restrict the annular input orifice 128 to the pump.

In order to be certain that the throttling

sleeves

224 and 225 are maintained in their rest positions (the positions shown in Figs. 2 and 4) under normal operating conditions (with no gas in the well), the

pockets

222 and 223 are connected through the lines 211 and the bleeder valves 210 to the branch line 208 and the line 209 to the output or high pressure manifold 92 of the pump 40. Therefore, when the

pockets

222 and 223 are connected through the line 212 to the sump line 215 (upon movement of the stem 202 to the right) the bleeder valves 210 establish a pressure drop between the line 209-228 and the pockets 222223 and the line 212 The bleeder valves 210, being interposed between the lines 208209 to the high pressure side of the pump and the pocket 222223, prevent the high pressure fluid from flowing immediately into the pocket 223 which would immediately force the sleeve 225 to the right.

If, however, the pressure differential between the input and output sides of the pump is reduced substantially or almost wiped out, it is necessary that the

pistons

201 and 204 and stem 202 move almost all of the way to the right in order that the annular orifice around the tapered stem 220 shall be as large as possible to create as large a differential as possible between the pocket 223 of the throttling sleeve 225 and the input pressure to the pump so that the input orifice 128 will be restricted to a lesser size.

The stem 202 has a second tapered section 231 leading to the radial bore 218 and, when the stern 202 moves to the right, providing an annular orifice between its end and a land 232 located between the pocket 219 and an annular groove 233 at the left of the piston 204. The groove 233 (see Fig. 6) communicates through a passageway 234 with a transverse bore 235 in a boss 236 on the counterbalancing valve 199. The bore 235 is connected by an adjustable bleeder valve 237 (see also Fig. 2) with a line 238 connected to the high pressure line- 207.

When the differential in pressure between the input and output sides of the main pump 40 is reduced to an extent such that the piston 201, stem 202 and piston 204 of the counterbalancing valve 199 are driven to the right a substantial distance, the orifice around the second tapered portion 231 of the stem 202 also opens but slightly later than the orifice around the first tapered section 220. When the orifice around the tapered section 231 opens, the high pressure line 207 is connected through the line 238, through bleeder valve 237 to the groove 233, the orifice around the tapered section 231, through the pocket 219, the radial bore 218, axial bore 217, cross bore 216 and annular port 214 to the line 215 to the sump line 84, Upon the establishment of this connection through the bleeder valve 237, a pressure drop is immediately established between the pocket 205 on the right face of the piston 204 and the groove 233 on the left annular face of the piston 204. This lowers the pressure at the left side of the piston 204 to a degree controlled by the amount this tapered orifice around the section 231 is opened and thus slows or stops the movement of the piston 204 and stem 202 to the right.

As the main pump input orifices 128 are throttled down, the pressure differential between the input and output sides of the pump approaches its normal 200 p. s. i., and the pressure differential between the fluid acting on the left end of the piston 201 and the right end of the piston 204 is re-established.

The fluid acting on the right side of the piston 204 then moves the piston 204, stern 202 and piston 201 to the left. This closes the annular orifices around the tapered section 231 (balancing the unit pressure on both sides of the piston 204) and around the tapered section 220 isolating the pocket 223 from the sump.

Fluid bleeds through the bleeder valve 2110 building up the pressure in the pocket 223 and, finally, starting to restore the throttling sleeve 225 to its open position, opening the main pump input orifices 128.

If the gas condition still exists, of course, the throttling sleeve 225 does not move entirely back but only to a position such that the pressure ditferential on the pump is maintained.

By proper setting of bleeder valves 210 and the counterbalancing bleeder valve 237 in relationship to each other and because of the fact that the positions of the counterbalancing valve 199 and the throttling sleeve 225 is a matter of pressure balance, the counterbalancing valve 199 and the throttling sleeve 225 float in an intermediate position between their normal and most abnormal positions. in end etfect, therefore, the throttling sleeve 225 floats with its tubular section 226 partially obstructing the input orifice 128 (during the up stroke) throttling down the input pressure to the pump in an amount directly proportional to the reduction in the work to be performed on the output side of the pump, i. e., in direct proportion to the gas pressure acting upon the column of production fluid in the well and the piston 44. Because the input pressure to the pump is reduced in direct proportion to the work to be performed at the output side of the pump, the load on the pump and, therefore, the load on the main driving engine for the pump is kept constant even though gas in varying amounts may be present in the well beneath the column of production fluid during the up stroke.

DOWNSTROKE When gas is present in the working pump below the traveling valve and above the standing valve during the down stroke of the jack piston 44, little resistance to the movement of the pump plunger downwardly is afforded. The column of production fluid standing in the well exerts pressure against the traveling valve in the pump plunger and holds the traveling valve closed. Instead of the normal load on the piston 44, i. e., the weight of the rod 45, the piston is pulled downwardly by the sum of the weight of the rod 45 and the column of production fluid. Therefore, the pressure in the fluid returning from the pumping jack 43 in the line 42 to the pump 40 is substantially higher than it normally would be. Because the average pressure in the counterbalancing tank 30 is, however, maintained at its normal level (by the air pressure control apparatus discussed above), when the pressure in the line 42 is higher than normal, the pump 40 has less work to perform in order to bring its output pressure up to the average pressure of the counterbalancing tank 30.

Again, as in the case of gas in the well during the up stroke, the input pressure to the pump (in this case from the pumping jack 43) is higher with respect to the output pressure and thus the pressure differential between input and output pressures of the pump is reduced. Since it is the objective to keep the pressure differential between the input and output pressures of the pump constant, the invention provides means for reducing the input pressure to the pump during a down stroke in the same manner as the reduction of input pressure to the pump during an up stroke.

During a down stroke the reversing valve 93 is at its right position (Figs. 2 and 4). Therefore, the line 42 from the pumping jack 43 is connected through the annular input orifice 134 to the input manifold 196 of the pump 40. The throttling sleeve 224 is located with respect to the input orifice 134 in the same manner as the sleeve 225 is to the orifice 123. The throttling sleeve 224 has a tubular section 239 which slides in an annular land 246 adjacent the outer side of the annular input orifice 134. As was the case with respect to the throttling sleeve 225, the throttling sleeve 224 has an outwardly directed radial rim 241 and input pressure is applied to its outer larger face 243 by fluid in an annular passageway 242.

Because the throttling sleeve 224 is connected in parallel with and functions identically with the throttling sleeve 225 and because the conditions prevailing in the pump are identical with those prevailing during the up stroke, operation of the counterbalancing valve 199 and its control over the throttling sleeve 224 are identical with those already described during the up stroke of the piston 44. The annual input orifice 134 is, therefore, throttled by the throttling sleeve 224 and the input pressure to the pump 40 during a down stroke reduced in direct proportion to the increase in input pressure or reduction in differential between input and output pressures of the pump 46*, i. e., in proportion to the reduction in load caused by gas in the well.

Having described the invention, I claim:

1. In surface hydraulicapparatus for operating a well pump that is subject to gas entering the well, said apparatus comprising, apumping jack, a piston in said jack, a well tubing, a rod connecting said jack piston to a production pump in said tubing, a counterbalancing tank and a working fluid pump connected in series between said jack and said tank, in combination, means for sensing variations in the work to be performed in said working fluid pump, and means controlled by said sensing means for interposing a pressure drop between said jack and said working fluid pump during a down stroke and between said counterbalancing tank and said working fluid pump during an up stroke, in accordance with decreases in the differential between pressures in said jack and in said tank caused by the action of such gas on the pro duction fluid column in said tubing.

2. In surface hydraulic apparatus for operating a well pump that is subject to gas entering the well, said apparatus comprising, a pumping jack, a piston in said jack, 2. well tubing, a rod connecting said jack piston to a production pump in said tubing, a counterbalancing tank and a working fluid pump connected in series between said jack and said tank, in combination, hydraulically actuated means responsive to the variations in pres sure differential across said working fluid pump for interposing a pressure drop between said jack and said working fluid pump during a downstroke and between said counterbalancing tank and said working fluid pump during an up stroke, in accordance with decreases in the differential between pressures in said jack and in said tank caused by the action of such gas on the column of production fluid in said tubing above said production pump.

3. In surface hydraulic apparatus for operating a well pump that is subject to gas entering the well, said apparatus comprising a pumping jack, a piston in said jack, 0. counterbalancing tank and a working fluid pump connected in series between said jack and said tank, in combination, hydraulically actuated means responsive to the variations in pressure differential across said working fluid pump for varying the input pressure to said working fluid pump.

4. In surface hydraulic apparatus for operating a well pump that is subject to gas entering the well, said apparatus comprising, a pumping jack, a piston in said jack, a well tubing, a rod connecting said jack piston to a production pump in said tubing, 9. counterbalancing tank and a working fluid pump connected in series between said jack and said tank, in combination, hydraulically actuated means responsive to variations in pressure differential across said working fluid pump for throttling the input one of the connections from said jack and said counterbalancing tank to said working fluid pump in accordance with any excess input pressure relative to output pressure between said pumping jack and said counterbalancing tank resulting from the action of such gas on the column of production fluid in said tubing.

5. In surface hydraulic apparatus for reciprocating the sucker rod of a pump that is subject to gassing, said apparatus comprising a pumping jack, a sucker rod piston in said jack and a counterbalancing tank, the improvement in means for pumping power fluid alternately to and from said jack and said tank that comprises, in combination, a positive displacement working fluid pump connected in series between the tank and the pumping jack, a reversing valve for alternately connecting the input and output sides of said working fluid pump to said tank and said jack, hydraulic means balanced by and at a desired pressure differential between the input and output sides of said working fluid pump, hydraulically actuated means for throttling the input side of said working fluid pump and normally held in inoperative position by the pressure on the output side of said pump, and variable means controlled by and responsive to an unbalance in said balanced means for reducing such holding effect in accordance with reductions in such pressure differential.

6. In surface hydraulic apparatus for reciprocating the sucker rod of a pump that is subject to gassing, said apparatus comprising a pumping jack, a sucker rod piston in said jack and a counterbalancing tank, the improvement in means for pumping power fluid alternately to and from said jack and said tank that comprises, in combination, a positive displacement working fluid pump connected in series between the tank and the pumping jack, a reversing valve for alternately connecting the input and output sides of said working fluid pump to said tank and said jack, hydraulic means balanced by and at a desired pressure differential between the pressure in said counterbalancing tank and the pressure beneath said piston in said jack, and means actuated by said hydraulic means in response to changes in pressure beneath said piston for throttling the input side of said working fluid pump.

7. In surface hydraulic apparatus for reciprocating the sucker rod of a pump that is subject to gassing, said apparatus comprising a pumping jack, a sucker rod piston in said jack and a counterbalancing tank, the improvement in means for pumping power fluid alternately to and from said jack and said tank that comprises, in combination, a positive displacement working fluid pump having an inlet manifold and an outlet manifold, a reversing valve communicating with both of said manifolds, hydraulic lines from said reversing valve to said tank and to said jack, said reversing valve being actuated at the ends of the stroke of said jack for alternately connecting said inlet and outlet manifolds to said tank and to said jack, hydraulically actuated means for throttling the input manifold of said pump, and balancing means connected to said inlet and outlet manifolds of said pump and balanced at a desired pressure differential therebetween for controlling the throttling effect of said hydraulically actuated means in proportion to reductions in the pressure differential between said input and output manifolds of said pump.

References Cited in the file of this patent UNITED STATES PATENTS 1,025,222 Wallace May 7, 1912 1,663,647 Brush March 27, 1928 2,049,233 Thomas July 28, 1936 2,374,822 Le Clair May 1, 1945 2,426,639 OLeary Sept. 22, 1947