US3453963A - Downhole fluid actuated pump assembly - Google Patents

Description

y 1969 G. K. ROEDER DOWNHOLE FLUID ACTUATED PUMP ASSEMBLY Sheet Filed 001;. 9, 1967 INVENTOR. GEORGE K. ROEDER MARCUS L. BATES vl/lfll'l'llfllIIfl/lllflllllfflll'lllflfllI/ll'ilI Ill!!! y 1969 G. K. ROEDER 3,453,963

DOWNHOLE FLUID ACTUATED PUMP ASSEMBLY Filed Oct. 9, 1967 Sheet 3 of 2 FIG. 6

"I ll INVENTOR.

254 ggoRc-xs K. ROEDER 22 MARCUS L. BATES United States Patent 3,453,963 DOWNHOLE FLUID ACTUATED PUMP ASSEMBLY George K. Roeder, P.O. Box 3931, Odessa, Tex. 79760 Filed Oct. 9, 1967, Ser. No. 673,754 Int. Cl. F04b 47/08; F1511 13/042 US. Cl. 103-46 Claims ABSTRACT OF THE DISCLOSURE A fluid operated pump assembly which is adapted to be located downhole in a well, and including a valve means, an engine means, and a pump means all connected together into a single unit. A high pressure supply of fluid is conveyed from the surface downward to the pump assembly which is located in the producing well strata, and where the valve means flow connects the high pressure fluid to the engine to thereby extract power from the fluid. The engine actuates the pump in a manner to lift produced fluid from the well, along with the spent power fluid.

Background 0 the invention Downhole fluid operated pump assemblies, sometime called hydraulic pumping units are known in the art. These pump systems eliminate the thousands of feet of sucker rod required to transmit the necessary force for pumping action from the surface to the bottom hole pump. The system generally requires a high pressure hydraulic pump which is located above the surface of the earth and which recirculates a portion of the produced fluid from the well back to the pump assembly located downhole in the well. A valve system interconnects the high pressure fluid with an engine to thereby move a pump shaft which in turn lifts fluid to the surface of the earth. This is all adequately described in the prior art patents to C. I. Coberly; Patent Numbers 2,081,223, 2,230,830, and 2,338,903.

The various prior art devices presently include a single engine or motor end, and it is common practice to connect two production ends, or pumps, to one motor power piston. In carrying out this expedient in deep wells, the operating pressure requirements of the engine increases in proportion to the hydrostatic head, and is sometime of a magnitude wherein further increase in operating pressure in order to attain a deeper setting results in pump failure. Since the maximum pressure to which an engine may be subjected is limited, the only remaining expedient available in order to extract more power from the surface hydraulic pumps is to increase the area and stroke of the piston located within the engine which in turn drives the pump. The last expedient has the obvious limitation of the physical size the piston which can be located within the cylinder of an engine. The advent of deeper holes has brought about smaller diameter casings which further complicates or precludes the use of larger pistons.

Summary The present invention relates to downhole fluid operated pump assemblies for use in lifting fluid from a fluid pro ducing strata associated with a well by utilizing hydraulic power or fluid provided from the surface of the ground and suitably conveyed to the pump assembly. The pump assembly may be generally described as being comprised of an elongated cylindrical unit having an upper end connected to the power fluid source, an outlet connected to a produced fluid flow means, and an inlet connected to or in communication with the fluid producing strata.

The pump assembly includes a valve means, a motor or engine end, and a pump means; all connected together into a single string or unit.

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The engine includes spaced apart cylinders each having a double acting reciprocatingly received piston therein. Each piston is connected to a rod with the rod being connected to the pump whereby reciprocation of the pistons also actuates the pump. The upper extremity of each cylinder is flow connected in parallel to a first common passageway. The lower extremity of each cylinder is also flow connected in parallel to a second common passageway. This configuration allows an unlimited number of cylinders and pistons to be series connected in parallel flow relationship to thereby increase the power of the engine.

The valve means includes an inlet for the high pressure fluid, an outlet for the spent fluid, and passageways alternately interconnecting the first and second common passageways with the inlet and spent fluid outlet respectively; whereby, the high pressure source of fluid is utilized in driving the pistons in a reciprocating manner within their respective cylinders.

The first common passageway is embodied herein as a hollow piston rod which communicates one side of each cylinder through a passageway located in the piston to thereby interconnect respective sides of the different cylinders in parallel relationship. The second common passageway is illustrated herein as an annulus located in the engine wall having ports leading into each opposite side of the cylinder with respect to the first common passageway.

The pump shaft is also hollow and communicates with a lowermost portion of the lowermost cylinder to thereby provide lubrication to the pump as well as an increased hydrostatic head on the pump shaft.

It is desirable to be able to extract suflicient power from the engine of a downhole pump assembly in order to actuate a multiplicity of series connected pumps to thereby lift produced fluid from extreme depths.

Therefore, a primary object of this invention is to provide the engine of a downhole pump assembly with means for increasing the piston area thereof so that the power fluid can apply suflicient force to thereby suitably actuate a pump.

Another object of this invention is to provide a downhole pump assembly with means whereby an increase in plston area may be attained within an engine thereof by adding additional stages of engines which in turn enables the installation of additional stages of pumps therewithin.

A still further object of the present invention is to provide a multistage engine, associated with a fluid operated pump assembly, which includes passageways therein through which power fluid can travel to various individual stages of the engine to thereby provide multiple staged plstons without interfering with the discharge of the fluid from the low pressure sides of the engine pistons.

Another object of this invention is the provision of a means whereby a multistage engine may be attained by the addition of several shorter single stage engines to thereby obtain a power increase without increasing the diameter of the overall pump assembly.

A further object of the present invention is the provision of a means whereby a longer multistage engine or motor end may be substituted for a shorter single stage engine end of a downhole pump, while still enabling operation of the entire pump assembly from a short bottom hole cavity wherein the pump assembly is operated in the free type system.

Another object of the present invention is the provision of a means associated with a downhole pump whereby fluid pressure used to provide the up-stroke movement of an engine piston can be utilized to exert a force against the bottom of the pump shaft to thereby reduce the danger of breaking the shaft which joins the multiple engine pistons with the pump pistons.

The above objects are attained in accordance with the present invention by the provision of a fluid operated pump assembly fabricated in a manner essentially as outlined in the above abstract. Other objects and advantages will become apparent in the details of construction and operation as hereinafter more fully described and claimed.

Brief description of the drawings With reference to the accompanying drawings, wherein like numerals, wherever possible, refer to like parts throughout, in which:

FIGURE 1 is a vertically sectioned view showing a fluid operated pump made in accordance with one embodiment of the present invention, with the pump being broken away into three different parts in order to enable one view of the entire device to be included on a single sheet of the drawings;

FIGURE 2 is a cross-sectional view taken along line 22 of FIGURE 1;

FIGURE 3 is a cross-sectional view taken along line 3-3 of FIGURE 1;

FIGURE 4 is a cross-sectional view taken along line 44 of FIGURE 1;

FIGURE 5 is a cross-sectional view taken along line 5-5 of FIGURE 1; and

FIGURE 6 is a cross-sectional view, with some parts being unsectioned, in order to illustrate a second embodiment of the present invention.

Description of the preferred embodiments Looking now to the details of FIGURE 1, in conjunction with FIGURES 2 through 5, wherein there is seen one view comprised of three fragmentary parts of the present invention which, when connected together along the indicated dashed line, constitutes an elongated crosssectional view of a fluid operated pump assembly made in accordance with the present invention, and its operative relationship with respect to an oil well casing and production tubing. As seen in the drawings, the device is comprised of a valve assembly 10, a first and second series connected engines 12 and 14, and a pump 16, all connected together and placed within a tubing which extends from a lower terminal end 20, with the lower end being located within a perforated casing 22. The production tubing extends to the surface of the ground and conducts flow of produced fluid and spent power fluid therethrough. The pump assembly is flow connected to a power tubing 24 which extends to a high pressure pump above the surface of the earth.

The power tubing is threadedly connected at 26 to a tubing connector 28. A main valve body 30 is attached to the tubing connector by a threaded connection 32 and further includes a lower threaded connection 34 formed at the upper terminal end of the outer peripheral wall surface 36 of the engine. A pump housing 38 is suitably connected to a middle plug 40 which has a valve system 42 located therebetween. A lower valve system 46 is interposed between the upper valve housing and a lower plug 48. A bottom tube 50 terminates in a bottom plug 52 which is sealingly received within the contoured lower seat member 54. Inlet 56 provides a flow of fluid from the perforated easing into the bottom plug of the pump assembly.

A longitudinally extending cylindrical rod extends through the pump, engine, and valve means where it forms a pilot or valve rod the upper terminal end of which is seen at 60. The valve rod is slidably received within a main valve element 62 which reciprocates about the rod and about a control sleeve 64. The rod receives a flat portion 66 which cooperates with the main valve in a manner which controls the vertical position thereof. Associated with the valve assembly is a first flow passageway 68 formed in the valve body. The passageway is in communication with a passageway 70 formed in the plug 71. The last named passageway communicates with the annulus 72 which is formed by the inside peripheral wall 36 and the outer wall surface of cylinder liner 73. The valve alternately connects annulus 72 to either the spent fluid port 74 or to the interior of the power tubing 24, depending upon the position of the main valve which in turn depends upon the position of the pilot rod. A second flow path 76 forms a flow path from each upper extremity of the engine cylinder 78 and is alternately connected either to the spent power port 74 or power tubing 24, depending upon the position of the main valve. When the main valve interconnects the power tubing to passageway 76, the passageway 72 is simultaneously connected to port 74, and vice versa.

The lower extremity 80 of each engine cylinder is provided with ports 82 communicating with passageway 72. Ports 84 connect the upper extremity of the uppermost engine cylinder with passageway 76. Each piston 86 includes an upper and lower shoulder 88 and 90, respectively, which in turn are connected to a hollow connecting rod. The connecting rod at 60 is solid above the flat 66, while it is hollow beginning with the circumferentially spaced passageways 95. Passageways communicate with the single passageway 96 and continue as seen at 97 into lowermost piston 86' where the passageway then is denoted by numeral 97' which exits into the circumferentially spaced passageways 95. It should be understood that additional cylinders and pistons may be arranged in series relationship below the lowermost piston 86'; however, for purposes of illustration it is deemed unnecessary to show more than two pistons and cylinders.

A plug 100 precludes flow of fluid from passageway 97' into hollow pump rod 104. Port 102 permits flow of fluid from below piston 86' into the hollow rod 104 where the flow continues along the passageway as seen at 106 since piston 108 has a longitudinally drilled passageway therethrough. The lower terminal end of the pump shaft is left opened as seen at 109 where the shaft is received by the balance tube 110.

Looking now to the details of FIGURE 6 wherein, so far as possible, like numerals thereof refer to like ele ments of the foregoing FIGURES 1 through 5. For example 274' corresponds to aperture 74 of FIGURE 1 and numeral 254 corresponds to numeral 54 of FIGURE 1. The fluid operated pump of FIGURE 6 is of the free pump system in that the entire fluid operated pump may be forced to the surface of the ground by merely reversing the direction of fluid flow, sometime called reversed circulation, as will be explained in greater detail later on. As seen in FIGURE 6, the pump assembly is provided with spaced apart upper packers 314, 316 located at the upper extremity of the device, with power tubing 312 providing the flow of high pressure into the inlet 224. The inlet is attached to the engine by an adaptor having a power fluid inlet 274 therein which communicates with inlet 224 to thereby provide a passageway for fluid flow from the source of power fluid, through the packers, and to the inlet 304 of valve 210 associated with engine 212. It will be noted that the valve and engine are inverted with respect to the configuration seen in FIGURES 1 through 5.

O-ring collar 318 cooperates with O-ring 320 thereby prevents the flow of high pressure fluid thereacross. Valve adaptor 306 includes spent power fluid outlets 274'. Pumps 238, 239 include outlets 242, 246, and 347 located adjacent their respective plugs, and with the outlet 246 being associated with both pumps 238 and 239.

Annulus 310 formed between the power tubing 312 and casing 222 forms a flow path for the spent power fluid from ports 274' and the produced fluid which flows from the pump valve system. The fluids flow through ports 308, into the annulus, and to an accumulator located above the surface of the ground. Seat member 254 cooperates with the lower extremity of the tool in the illustrated manner of FIGURE 6 to thereby enable produced fluid from the strata to flow into the centrally located passageway of the seat member, into the lower extremity of the pump assembly, where the fluid then flows through internal passageways to the series connected pumps.

Operation In operation of the embodiment illustrated in FIGURES 1 through 5, the high pressure fluid is maintained within the power tubing 24. With the main valve 62 in the illustrated position of FIGURE 1, high pressure fluid flow is conducted along the path defined by the annulus which is formed between the rod 60 and the valve. Accordingly, fluid flows from the power tubing, through the aligned ports of the main valve at 69, and into the radially spaced apart passageways 68 which communicate with the annulus 72 by means of the radially spaced inclined slots 70 of the plug 71. Since the annulus 72 is now filled with power fluid, and since the lower extremity of each cylinder is provided with ports 82, 82, it will be appreciated that any number of longitudinally arranged cylinders may be interposed between those illustrated herein, since each will be provided with a source of parallel fluid flow which will cause a double acting piston associated therewith, such as piston 86 or 86, to move in an upward direction.

Upward movement of the topmost piston displaces fluid from the top of the cylinder associated therewith. With the engine in the illustrated position of FIGURE 1, spent power fluid is exhausted therefrom by means of flow passageways 95, 96, and 95', 96' which are connected together by means of the hollow connecting rod seen at 60 and 92. As the power pistons of the engine each reciprocate in an upward direction, fluid contained above the lowermost piston is sealed from chamber 80 by seal means or packer 94 and accordingly must flow into the hollow connecting rod by means of passageways 95, 97, and 97. Plug 100 precludes flow of fluid toward the pump section of the assembly. Fluid continues to flow to the uppermost portion of the uppermost portion of the uppermost cylinder by means of passageways 96, 95 whereupon the fluid then enters passageway 84 of the lug 71. Passageways 84 are radially spaced about the plug and alternate with the sloped radially spaced passageways 70. Fluid continues to flow through the plug and into the second flow path 76, through the main valve, and out of port 74. As the pistons each move upward, pilot rod 60 is vertically raised until flat 66 cooperates with the main valve and control sleeve in a manner to cause movement of the main valve from a first to a second position, whereupon the second flow path 76 is then connected to the source of power fluid located within tubing 24, while simultaneously the first flow path 68, 72 is connected to the spent power outlet port. This action of the main valve causes the high pressure fluid to flow along parallel paths to the upper parts of the engine cylinders, while the spent power fluid outlet port is connected to the lower extremity of each cylinder along the before described flow path associated with the annulus 72. For greater detail of the intricate parts and other operational aspects of the valve system, attention is directed to FIGURE 1 of Coberlys Patent Number 2,081,223. Since the valve system is sufficiently explained in this prior art patent, further details are readily available therein.

As will now be evident to those skilled in the art, an unlimited number of stages or engine cylinders may be interposed bet-ween the upper and lower cylinders of the engine of the present device. This expedient provides an unlimited amount of power to be realized or made available from the engine section of a downhole hydraulically actuated pump assembly. The number of stages which may be interposed between the upper and lower stages of FIG- URE 1 is limited by the design of the rod which connects the pump 16 to the lowermost engine 14.

In order to decrease failure of the pump rod, a hydrostatic head in the form of high pressure fluid is maintained on the pump rod each upstroke of the pump by the provision of the port 102 which communicates with passageway 106 of the pump piston rod 104. As is seen in the drawings, this passageway extends from below the lowermost engine piston 86 to the lower open terminal end 109 of the rod. The rod is received within the balance tube 110, with the upper end of the tube being rigidly aflixed to the lower plug. By utilizing a portion of the power fluid in this manner, the same pressure which forces the engine pistons in an upward direction also exerts its force against the bottom of the lower rod in a manner which has been found to reduce the danger of breaking the rods which interconnect the various pistons of the pump device.

As will now be evident to those skilled in the art, the configuration of the device illustrated in FIGURE 1 is adapted to be used in the fixed type system. In this system, when it is desired to remove the pump assembly from the well, the power tubing 24 must be removed from the borehole, carrying along with it the entire fluid pump apparatus. Where it is desired to use the pump assembly of FIGURE 1 in the free pump system, the invention is best practiced by arranging the various components in accordance with the teachings of FIGURE 6.

As seen in this system, spaced apart packers 314, 316 at the upper extremity of the free pump assembly permit the flow of power fluid downwardly to the pump through tubing 312, where the fluid enters ports 224, flows through a check valve at the top of the assembly, where the power fluid exists at 274. The engine 212 and valve assembly 210 are located between the illustrated O-ring collar and a packer, with the engine and valve assembly being inverted with respect to the teachings of FIGURE 1. Therefore, the power fluid enters the valve assembly at 304 where the engine 212 extracts energy therefrom, with the spent power fluid exhausting about the valve adapter 306 by means of the spent power fluid outlet 274'. The fluid admixes with produced oil which is being pumped by the various stages 238, 339 of the pumps. Produced fluid and spent power fluid flow downwardly and through the production ports 308 where the fluid is then pumped to the surface of the earth along the annulus 310. Seat 254 ccoperates with the lower extremity of the pump assembly in the usual manner.

This configuration, as seen in FIGURE 6, enables the pump to be installed into a borehole by lowering the pump into the power tubing, whereupon power fluid will force the pump vertically downward until the bottom plug sealingly mates with the centrally aligned passageway of seat 254. The pump remains in this operative position with fluid being pumped to the surface in the above described manner. When it is desired to remove the pump from service, circulation is reversed, thereby forcing the entire pump assembly to the surface of the earth.

An added advantage of the configuration of FIGURE 6 lies in the unlimited number of stages which may be added to engine 212, since the upper spaced apart packer sealingly cooperates with the inside peripheral wall surface of the power tubing while the distance between the spaced apart O-ring collar and seat member remains constant. Therefore, should it be desired to add additional engine stages to an existing single stage engine, this expedient may be carried out by merely fabricating the upper portion of the pump assembly in accordance with the teachings of FIGURES 1 and- 6. The details of adding multistage pumps to an engine are known to those skilled in the art, and accordingly, need not be further detailed herein.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention as claimed.

I claim:

1. A fluid actuated pump assembly (10, 12, 14, 16) having an engine (12, 14) connected to a pump (16), a

valve means (10) adapted to be connected to a fluid power source (24) and an exhaust (74) for controlling fluid flow to and from the engine;

said engine (12, 14) having means forming a first flow path (68) and a second flow path (76); said engine having spaced apart cylinders (73, at 12 and 14) including a double acting piston (86, 86) reciprocatingly received within each cylinder, a common connecting rod (60, 92, 60, 104) attached to each piston (at 88, 90) and to the pump (16);

means including said first flow path interconnecting the lower extremity of each cylinder to thereby provide a path of fluid flow (80, 72, 70, 68 and 82', 72, 70, 68);

means including said second flow path forming a passageway into the upper portion of the uppermost cylinder (84, 76) and further including means forming a passageway (95, 96, 97, 95', 97') through said connecting rod (60', 92) and into the upper portion (78) of each cylinder to thereby place the fluid adjacent the upper portion of each piston (88) in communication with the second flow path;

the valve means normally assuming a first and second position and connecting said first flow path to the power source and said second flow path to the exhaust when the valve means assumes the first position, and; the valve means connecting said first flow path to the exhaust and said second flow path to the power source when the valve means assumes a second position; whereby:

said engine reciprocatingly actuates the pump in response to the presence of the fluid power.

2. The improvement of claim 1 wherein said engine includes still another cylinder located between said spaced apart cylinders, and including a double acting piston reciprocatingly received therewithin;

means flow connecting the upper portion and lower portion of said other cylinder to the upper portion and lower portion of said spaced apart cylinders.

3. The improvement of claim 1 wherein said pump includes a pump cylinder having a pump piston reciprocatingly received therein; means forming a produced fluid inlet and outlet in cooperation with the upper and lower pump cylinder for conveying produced fluid away from the pump; said pump piston including a pump rod con nected to the lowermost engine piston with said pump rod forming a part of said connecting rod;

means forming a passageway inside said pump rod with the last said passageway being in communication with the lowermost portion of the lowermost said engine cylinder;

a balance tube depending from the lower extremity of said pump cylinder;

said pump rod having a lower terminal end reciprocatingly recived within said balance tube; whereby, fluid pressure in said lowermost cylinder is transferred through said pump rod to thereby exert a pressure against the lower terminal end of said rod.

4. A fluid operated pump assembly for operation downhole in a well and adapted to convey power fluid from the surface of the ground downwardly to the pump assembly, spent power fluid upwardly to the surface, and fluid produced by the well upwardly to the surface; the pump assembly having a valve section, an engine section, and a pump section all connected together in series relationship to form a string of components, with the valve section controlling the flow of power fluid into the engine to thereby enable the engine to extract power from the fluid, and with there being connecting means by which the engine section drives the pump section to enable the pump to perform the stated function of lifting fluid upwardly; the improvement comprising:

said engine section including spaced apart cylinders each having a piston reciprocatingly received therein, said pistons being connected together by a hollow connecting rod, each piston including an upper and lower face with said upper face being in communication with an upper portion of the cylinder within which the piston reciprocates, means forming a passageway flow connecting said upper face of each said piston with the interior of said hollow connecting rod, whereby; flow into the upper portion of one of said cylinders will also flow through said hollow connecting rod and into the upper portion of another said cylinder; means forming a first flow path which is in fluid communication with said lower face of each said piston;

means forming a second flow path; the upper most portion of one of said cylinders being connected to said second flow path;

said valve section having means forming a power fluid inlet, a spent power fluid outlet, and further including means for connecting said first flow path of said power fluid inlet while simultaneously connecting said second flow path to said spent fluid outlet, when said valve means is in a first position; and, for connecting said first flow path to said spent fluid outlet while simultaneously connecting said second flow path to said power fluid inlet, when said valve means is in a second position;

whereby said engine pistons drive the pump to thereby convey fluid in the above stated manner.

5. The improvement of claim 4 wherein said engine includes still another cylinder having a piston reciprocatingly received therein;

said pump includes a pump cylinder having a pump piston reciprocatingly received therein; means forming a produced fluid inlet and outlet in cooperation with the pump cylinder for providing the stated function of conveying fluid upwardly; said pump piston including a pump rod connected to the lowermost engine piston;

means forming a passageway inside said pump rod and in communication with the lowermost portion of the lowermost said engine cylinder;

a balance tube depending from a lower end portion of said pump cylinder;

said pump rod having a lower terminal end reciprocatingly received within said balance tube; whereby, fluid pressure in said lowermost cylinder is transferred through said pump rod to thereby exert a pressure against the lower terminal end of said rod.

6. The improvement of claim 4 wherein said engine includes still another cylinder having a piston reciprocatingly received therein; said cylinder being located between said spaced apart cylinders, with the upper and lower portions of said other cylinder having means flow connected to the upper and lower portions of said spaced apart cylinders.

7. The improvement of claim 4 wherein said pump includes a pump cylinder having a pump piston reciprocatingly received therein; means forming a produced fluid inlet and outlet in cooperation with the upper and lower pump cylinder for providing the stated function of conveying fluid upwardly; said pump piston including a pump rod connected to the lowermost engine piston;

means forming a passageway inside said pump rod and in communciation with the lowermost portion of the lowermost said engine cylinder;

a balance tube;

said pump rod having a lower terminal end received Within said balance tube; whereby, fluid pressure in said lowermost cylinder is transferred through said pump rod to thereby exert a pressure against the lower terminal end of said rod.

8. The improvement of claim 4 wherein said valve means normally cyclically assumes a first and then a second position in response to the presence of power fluid and to the reciprocatory action of the pistons.

9. In a multistage engine for actuating a production pump or the like,'wherein the engine includes an upper and a lower cylinder, with each cylinder having a double acting piston reciprocatingly received therein to thereby divide each cylinder into upper and lower chambers, and with each piston being connected together by a common rod, the improvement comprising:

means forming a passageway through said rod and through at least one said piston to thereby flow communicate the upper chamber of the upper cylinder with the upper chamber of the lower cylinder; means forming another passageway which communicates the lower chamber of the upper cylinder to the lower chamber of the lower cylinder; a source of power fluid, means forming an exhaust for flow of spent power fluid away from said engine, and a valve means flow connected to said source of power fluid, said exhaust, said passageway through said rod, and said another passageway; said valve means assuming a first flow position and a second flow position in response to the reciprocation of said pistons; said valve means, when in the first flow position, conducts flow of power fluid to each of the upper chambers of each cylinder while at the same time conducts flow of spent power fluid from each of the lower chambers of each cylinder to the exhaust, and said valve means, when in the second flow position, conducts flow of power fluid to each of the lower chambers of each cylinder while at the same time conducts flow of spent power fluid from each of the upper chambers of each cylinder to the exhaust; whereby:

said pistons, when suitably connected to a pump, reciprocatingly actuates the pump.

10. The improvement of claim 9 wherein said production pump includes a production cylinder with a production piston reciprocatingly received therein, said lower piston is connected to said production pump piston by a pump rod; said pump rod downwardly depending from said pump piston for a limited distance;

a balance tube downwardly depending from said production cylinder and reciprocatingly receiving the terminal end of said pump rod therein;

means forming a flow path from said lower chamber of said lower cylinder, through said pump rod, and into said balance tube to thereby utilize the fluid pressure exerted within the lower chamber of said lower cylinder to exert a force upon the lower terminal end of the rod.

References Cited UNITED STATES PATENTS 1,543,488 6/1925 Todd 103-46 2,245,501 6/1941 Richardson 103-46 2,726,605 12/1955 Tebbetts 103--46 25 ROBERT M. WALKER, Primary Examiner.

US. Cl. X.R. 91-411

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