US2670685A - Fluid-operated well pumping apparatus with hydraulic shock absorber - Google Patents

Description

C. J. COBERLY ATED March 2, 1954 FLUID-OPER WELL PUMPING APPARATUS WITH HYDRAULIC SHOCK ABSORBER 2 sheets-sheet 1 Filed April 20, 1951 5). HIS HTTONEYS.

HARP/.s merg/F0575@ a; Hmm/5 @Y March 2, 1954 C, J, CQBERLY 2,670,685

FLUID-OPERATED WELL PUMPING APPARATUS WITH HYDRAULIC SHOCK ABSORBER Filed April 20', 1951 2 sheets-sheet 2 PRESS U95 TIME.

CLARENCE d. COE/QLYV BY H/S HTTO/VIEYTS. HARRIS, MECH, P06-Te@ HA @Rvs Patented Mar. 2, 1954 FLUID-OPERATED WELL PUMPIN G APPARA- TUS WITH HYDRAULIC SHOCK ABSORBER Clarence J. Coberly, Los Angeles, Calif., assignor to Dresser Equipment Company, a corporation of Ohio Application AprilZO, 195,1, Serial No. 222,045

My invention relates in general to apparatus for pumping uids from wells and, more particularly, to an apparatus which includes a reciproeating pump of the iluid-operated type, a primary object of the invention being to provide an apparatus of this character having means associated therewith for absorbing uid pressure variations which may impose hydraulic shock loads on the system.

Reference is hereby made to my copending applications Serial Nos. 18,768 and 26,305, led April 3, 1948, and May 11, 1948, respectively, now Patents Nos. 2,576,923 and 2,576,924, respectively.

Fluid-operated pumps are used extensively in the oil industry for pumping oil from wells and are well known in the art so that a detailed description thereof herein'is unnecessary, an example of such a pump being disclosed in my Patent No. 2,134,174, issued October 25, 1938. Briey, such a duid-operated pump comprises a motor section and a pump section and is set in the well at the level from which oil is to be pumped. A power tubing for conveying operating fluid under pressure to the pump and a production tubing for conveying oil and otherfluids discharged by the pump tothe surface are connected to the motor and pump sections, respectively. The operating lluicl is usually clean crude oil and will be referred to hereinafter as the power oil. For convenience, the combination of uids pumped, which may include oil, Water, etc., will be referred to hereinafter as the production iuid. In the event that the spent operatingfluid is discharged into the production tubing, the production fluid also includes such spent operating fluid.

The motor section of the pump includes a cylinder having a piston therein and includes an engine valve mechanism for admitting the power oil into at least one end of the motor cylinder periodically so as to reciprocate the motor piston. The pump section includes a cylinder having a piston therein which is connected to the motor piston so that the reciprocating motion of the motor piston is communicated to the pump piston. The latter draws fluid from the well and discharges it into the production tubing through suitable intake and exhaust valve mechanisms. Fluid-operated pumpsl normally used in the oil industry may be of either the single-acting or double-acting type.

In order to prevent excessive wear and possible breakage of the various parts of such fluidoperated pumps, and in order to prevent possible damage to otherl components of the installation 16 Claims. (Cl. 103-46) in which the pump is incorporated, it is essential to minimize any 'shock loads which may originate in the pump, the provision of an apparatus for absorbing such shock loads being the primary object of the present invention. Shock loads may be developed in the pump under various conditions of operation, one of these being the condition resulting when the load on the pump piston decreases suddenly due, for example, to the presence of air or gas in the pump cylinder. The iiuid entering the well casing from an adjacent oil producing formation may contain considerable quantities of natural gas, the amounts present depending upon the amount present in the formation and depending upon prevailing conditions of pressure, temperature, etc. Sudden decreases in the load on the pump piston may also result if the well is operated beyond its capacity so that air or gas is drawn into the pump cylinder as a result of recession of the iiuid level below the pump inlet. In some instances, the well casing may be connected to a vacuum line so that the pressure on the gas may be less than atmospheric. Also, in elds subjected to partial vacuums, air may be drawn into the well casing if it is left open.

Since the pump piston reduces the pressure in the pump cylinder below that prevailing in the well as it draws Well fluid into the pump cylinder, any gas present in the well fluid in solution or in suspension may be liberated in the pump cylinder with the result that a quantity of liquid suicient only to partially lill the pump cylinder is drawn thereinto, the balance of the pump cylinder being filled with gas. Similarly, the pump cylinder may be partially lled with air or gas at a low pressure if the well is pumped beyond its capacity. Consequently, when the direction of movement of the pump piston is reversed, the pump piston acts only on the air or gas in the pump cylinder for at least a portion of the stroke. Since the air or gas is highly compressible, it olers but little resistance to movement of the pump piston so that the motor and pump pistons, being directly connected, may accelerate to an extremely high speed. In many instances, the speed attained by the pistons may greatly exceed their normal operating speed, the reason for this being that a considerable amount of potential energy is normally stored in the `power, oil supply system at the pressures usually employed because of the compressibility of theV column of power oil in the power tubing andthe expansibility of the power tubing. Such a potential energy is released when the load on the pump piston decreases and may accelerate the motor and pump pistons to a speed far in excess of their normal operating speed.

When the pump piston, moving at an abnormally high speed, strikes liquid in the pump cylinder, severe shock loads are developed which may cause extensive damage to the pump in the form of excessive wear, scoring, seizing and even breakage of parts. Moreover, pressure surges of considerable magnitude may Vbe .produced in the power oil and production huid columns above the pump and may result in abnormal stressing of and possible damage to other. components ofthe system. Also, if the well fluid being pumped contains a large percentage of Water, which is frequently the case, shock loads originating in the pump may be particularlyksevere, the' reason for this being that the compressibilityofwater is less than that of crude oil. Consequently, when water is present, the Compressiblitv of the production fluid column above the. pump is materiallr reduced, as compared to the compressi- `bility of a production fluid column consisting 'of relatively pure crude cil, or a mixture of crude 'oil and. ses, so. that the amount of energy which itis capable of absorbing is materially decreased.

also., iff air. is drawn into the pumpv under shock y would .otherwise be attained, an example of such a governor. Vbeing disclosed in my Patent No. 2,311,157, issued February 1-, 19431. However, due to the. fact that such a governor tends to operate only after the conditions which result in acceleration of the motor. and pump pistons have already developed, there may be some lag in its operation. Consequently, even it a governor is employed, shock loads of undesirably large Amagnitude may be. produced., although such shock toads. are, of coursagreatly reduced as a result ot 'the use of the governor. A

Even when a'fluid-olerated pump ofthe type 'disclosed in'my Patent No. '2,134,174ffor example, is operatmg under normal conditions, Si. e., `when little or no Vgas'or air is present in the 'well duid 'being pumped, pressure pulsations 'are produced in both the power oil and the production fi-uid columns due to the fact that the motor and pump Vpistons stop momentarily at the ends oftheir strokes. This results in an increase in the pressure of the power oil and a decrease inthe pressure of the production fluid. The amount of dwell at the ends of the strokes may be controlled 'with van engine valve of the type disclosed in my Patent No'. 2,134,174, it bei-ng desirable to" have sufficient dwell to allow time for the pump valves to seat. If'the time allowed for the pump valves to seat is too great, excessive pressure pulsations in both the power oil and production fluid columns result, and, if the time allowed isv too small, serious 'pressure pulsations in the productionuid columns result. I-t is impractical and, in many instances, impossible to eliminate such Apressure l pulsations, by regulating the time allowed for the pump valves to seat. Although the magnitude of such pressure pulsations is small when the pump is operated at moderate speeds and when the pump cylinder lls properly, such pressure pulsations may be suciently large to cause serious diiculties at high pump speeds. Severe stresses may be developed in various components of the installation bythe pulsations ii the frequency of the reciprocating motion of the motor and pump pistons coincides with either the natural freduency oi; oscillation or one of the harmonics of either the power oil or the production fluid colabove theA pump, i. e., if the frequency of thepressure pulsations developed in the columns asa'result 'ofj'theA reciprocating motion of the motor and pump pistons coincides with either the natural ifreguencyor one of the harmonics of one of the columns.' These columns are only modcrately damped so that standing pressure waves of a magnitude sufficient to develop abnormal stresses in various components of the installation may be produced under such resonant operating conditions.

Since the natural frequencies of the power oil and production uid columns are usually relatively llow Vas compared to the frequency oi' reciprocation of the motor and pump pistons during normal operation, it is usually possible to avoid operating the pump. in .phase with the natural frequencies lof the columns. However, it is virtually impossible 'to select an operating speed for the pump which avoids both the lnatural frequencies of the power oil and production fluid columns and all of the harmonics thereof due to the fact that the intervals between the natural frequencies and the first harmonics and the intervals between harmonics are relatively small.

Another. factor which vmakes it difficult to 'avoid both the natura1 frequency and all 'of the harmonics of the production fluid column in particular is that the natural frequency or this -column varies with variations in the proportions ofV gas, cil and water in the production fluid. -Consequentin since resonant operating 'conditions cannot be avoided readily by a selection 'ot a suitable yoperating 'speed' for the pump., it is desirable to reduce the magnitude of the pressure surges resulting from the reciprocatory nature of the operation -of the Vpump so as to avoid producing standing pressure wavesfoi excessive magnitude, the` provision of an apparatus capable of absorbing such pressure surges being an important 'object of the present invention. In fluideopcr'ated pump installations of the type under consideration', the power oil and production fluid columns are semi-closed systems and do not communicate with each other freely in both Vdirections because the Huid-operated' pump is interposed between them, the l direction -and amount of communication possible depending upon thev positions ofthe engine and pump valves. With closed columns Ieach terminating in a valve, serious Water hammer may result from sudden vclosing V'oi'.- the valves with 4high tit-uid 'velocities therethrough. In all cases olf 'normal operation and in many cases of shock resulting from mal- `functionir-ig Vof the pump valvesor improper nlling of the pump cylinder, the pressure surges in the two columns are out of phase land may be 'cancelled out or greatly. reduced by balancing-the two columns against each other, which is another important object Yof my invention.

More` specifically, an object 'istoprovide a shock absorber which includes a movable iiuid separating means, auch, as. a piston, havingopposed flrst and second surfaces which are exposed to the fiuid pressures obtaining in the power and production tubings, respectively, the areas being so related to each other and to the fluid pressures in said tubings that the piston is substantially `balanced hydraulically.

Another object is to provide such a shock absorber having a piston, or other fluid separating means, which includes a third surface disposed on the same side thereof as said first surface and exposed to the fluid pressure obtaining in the well substantially at the level of the pump so that the power oil and well fluid pressures act in the same direction on the piston, the three areas being so related in size that the piston is hydraulically balanced.

Another object is to provide a shock absorberI of the foregoing character` wherein the piston is provided with a stem projecting therefrom into a substantially closed chamber filled with liquid which is adapted to absorb or dampen sudden fluid pressure surges in one or both of the tubings. A further object is to provide such a device in which the interior of the closed chamber is connected by a small restricted orifice to one of the tubings so that the fluid pressure normally existing in the chamber is the same as the fiuid pressure in one of the tubings. I prefer to make this orifice connection to the production tubing.

Other objects of the invention are to provide a shock absorber which may be connected directly to a pump with which it is to be used so that the piston therein may be exposed to the fluid pressures obtaining in the power tubing, the production tubing and the well at points in close proximity to the pump, whereby pressure surges originating in the pump are absorbed substantially instantaneously, and to provide a compact device which occupies a minimum of space in a well.

The foregoing objects of my invention and the advantages suggested thereby, together with various other objects and advantages which will become apparent, may be attained with the exemplary embodiment which is illustrated in the accompanying drawings and which is described in detail hereinafter. Referring to the drawings:

Fig. l is a vertical sectional View illustrating a pumping installation which embodies the invention as installed in a well;

Fig. 2 is an enlarged, vertical sectional view taken along the broken line 2--2 of Fig. 1 and showing an upper portion of a shock absorber of the invention connected to a lower portion of a fluid-operated pump;

Fig. 3 is an enlarged, vertical sectional View taken along the broken line 3-3 of Fig. 1 and showing the lower portion of the shock absorber, Fig. 3 being a downward extension of Fig. 2; and

Fig. 4 is a graph illustrating the operation of the shock absorber.

Referring particularly to Fig. 1, I show a well casing I9 which extends downwardly from a casing head II into an oil producing formation of a well, the lower end of the casing being provided with perforations I3 through which well fluid, i. e., oil, water, gas, etc., from the oil producing formation may flow into the casing. A production tubing I4 is suspended from a tubing head I5 which forms an intermediate part of the casing head I I and extends downwardly through the casing I9 into the well fluid in the lower portion thereof. The lower end of the produc` tion tubing I4 is equipped with a tapered seat i1 which is adapted to receive and support an inlet fitting I8. A huid-operated pump I9 is disposed in the production tubing I4 and is connected to the lower end of a power tubing 20 for conveying power oil to the pump, the power tubing being suspended from a cap member 2| of the tubing head I5 and extending downwardly through the production tubing. A shock absorber 22 of the invention is interposed between the inlet fitting I8 and the pump I9 in the particular construction illustrated in the drawings, the shock absorberbeing connected to the inlet fitting at its lower end and to the pump at its upperend.

The duid-operated pump I9 per se forms no part of the present invention and is not shown in complete detail in the drawings. The pump I9 may, for example, be of the type disclosed in my aforesaid Patent No. 2,134,174, or may be of any other suitable type, as is well known in the art. As best shown in Fig. 1 of the drawings, the pump I9 includes, in general, an engine or motor piston 2ty which is reciprocable in a motor cylinder 21, and includes a pump piston 28 which is reciprocable in a pump cylinder 29, the two `pistons being directly connected by a rod 3U.

Connected to and extending upwardly from the motor piston 26 is a pilot rod 3|, and connected to and extending downwardly from the pump piston 28 is a lower rod 32. As best shown in Fig, 2, the pump I9 is provided at its lower end with a fitting 34 having a bore 35 therein, and is provided with a continuous passage 39, Fig. 1, which communicates at its upper end with the I' power tubing 20 and which communicates at its lower end with the bore 35 and with the shock absorber 29 as will be discussed in more detail hereinafter, the passage 36 extending through the pilot rod 3|, the motor piston 26, the intermediate rod 30, the pump piston 28 and the lower rod 32.

The general operation of the pump I9 is well known in the art, being described in detail in my Patent No. 2,134,174, and needs be described only Y briefiy herein. The power oil, which is preferably clean crude oil, is delivered under pressure to the tubing head I5 through a supply pipe 40 and flows downwardly through the power tubing 20 to the pump I 9. Such power oil is introduced alternately into opposite ends of the motor cylinder 21 in the case of a double-acting pump by a suitable valve mechanism, notshown, so as to reciprocate the motor piston 26, the reciprocatory motion of the motor piston being communicated to the pump piston 28 by the intermediate rod 30. Well fiuid is introduced alternately into opposite ends'of the pump cylinder 29 by a suitable valve mechanism, not shown, and is vdischarged into the production tubing I4 as production fiuid by the pump piston 28, the production uid subsequently fiowing upwardly through the tubing I4 to the surface and into a discharge pipe 4I. As will be discussed in more detail hereinafter,

the well fiuid enters the pump I9 by way of the inlet tting I8 and the shock absorber 22, the tting 34 at the lower end of the pump being provided with a plurality of passages 42 through which the well'fiuid may flow from the shock absorber into the pump, as best shown in Fig. 2.

Referring particularly to Figs. 2 and 3, the shock absorber 22 includes a tubular housing section 46 which is threaded at its upper end onto the fitting 34'and which is threaded at its lower end onto a fitting 41, another tubular housing section 48 being threaded at its upper `.end onto such pressure pulsations are absorbed being considered in detail in the following paragraph.

Referring particularly to Fig. 4 of the drawings, the numerals 85 and 86 indicate oscillograph curves showing, respectively, typical pressure pulsations encountered in the power oil and production fiuid columns whena pump vsuchas the pump IS is used without the shock absorber 22. It will be noted that the power oil pressure rises at the ends of the strokes of the motor and pump pistons 26 and 28, see curve 85, and that the pump discharge pressure or production fiuid pressure drops at the same time, see curve 8S, the pressure pulsations in the two columns being of approximately the same magnitude and of opposite sign. The rise in pressure in the power ltubing 20 and the drop in pressure in the production tubing I4 cause the shock absorber piston 5l to move downwardly against the pressure of the oil in the'chamber 63 so that the energy producing such movement is absorbed by compression of the oil in this chamber, and also by compression to some extent of the production fiuid. The net result is that the pressurein the power tubing 2B is decreased and the pressure in the production tubing I4 is increased, the resultant pressure in the two columns being approximately as indicated by the oscillograph curve 8l in Fig. 4. Thus, it will be apparent that, in eect, the shock absorber 22 causes the rise in power oil pressure and the drop in production iiuid pressure to cancel out, which is an important feature of the invention.

By designing the device so that the area of the fourth surface 8| is small relative to the volume of the chamber 63, the amount of surge energy which the liquid in the chamber will absorb is relatively great.

Although I have disclosed an exemplary embodiment of my invention herein for purposes of illustration, I do not intend to be limited specifically thereto since various changes, modifications and substitutions may be incorporated in the embodiment disclosed without necessarily departing from the spirit of the invention. Various other changes may also be made without departing from the spirit of the invention. Consequently, I hereby reserve the right to all changes, modifications and substitutions as properly come within the scope of the invention as set forth in the appended claims.

I claim as my invention:

l. In an apparatus for pumping fluid from a well, the combination of: a fluid-operated pump in the well; a first tubing extending into the well and connected to said pump, said first tubing being adapted to convey operating fluid to said pump to operate same; a second tubing extending into the well and connected to said pump, said second tubing being adapted to convey from said pump fiuid discharged thereby; and a shock absorber connected to said pump, said shock absorber including movable fiuid separating means having four transverse areas at leastone of which is on one side thereof and at least one other of which is on the opposite side thereof, including means for exposing one of said areas to fiuid pressure obtaining in said first tubing, including means for exposing another of said areas to fluid pressure obtaining in said second tubing, including means for exposing still another of said areas to Afluid pressure obtaining in the well substantially at the level of said pump, and including means for applying a fourth fiuid pressure to the fourth of said areas.

2. In a shock absorber for use in a well pumping apparatus which includes a fluid-operated pump adapted to be set in a well and having first and second tubings thereto, the first tubing being adapted to convey operating fluid to the pump to operate same and the second tubing being adapted to convey from the pump fiuid discharged thereby, the combination of movable iiuid separating means having four effective areas at least one of which is on one side thereof and at least one other of which is on the opposite side thereof, means for exposing one of said areas to fiuid pressure obtaining in the first tubing; means for exposing another of said areas to fiuid pressure obtaining in the second tubing; means for exposing still another of said areas to fluid pressure obtaining in the well substantially at the level of the pump; and means for applying to the fourth of said areas a fluid pressure sufiicient to balance any net pressure force differential resulting from the pressures applied to the other three areas.

3. A shock absorber according to claim 2 wherein the means last defined includes a chamber of variable volume one wall of which is defined by said fourth of said areas, said chamber being adapted to conne a liquid the pressure of which is adapted to be applied to said fourth of said areas so as to resiliently balance said net pressure force differential.

fl. In a shock absorber for use in a pumping apparatus which is adapted to be set in a Well and which includes a fiuid-operated pump having first and second tubings connected thereto, the first tubing being adapted to convey operating fluid to the pump to operate same and the second tubing being adapted to convey from the pump fluid discharged thereby, the combination of a cylinder; a piston disposed in and reciprocable longitudinally of said cylinder, said piston having first and third transverse areas on one side thereof and having second and fourth transverse areas on the opposite side thereof; means including a passage adapted to communicate with the first tubing for exposing said first area of said piston to fiuid pressure obtaining in the first tubing; means including a passage adapted to communicate with the second tubing for exposing said second area of said piston to fluid pressure obtaining in thel second tubing; means for exposing said third area of said piston to fluid pressure obtaining in the well, including a passage communicating with the well substantially at the level of the pump; and a chamber which is adapted to contain a liquid and one wall of which is defined by said fourth area of said pi-ston so that the pressure force applied to said fourth area of said piston by a liquid in said chamber resiliently balances any net pressure force differential applied to said piston by the pressures applied to said first, second and third areas.

5. A shock absorber as defined in claim 4 wherein said fourth area is small as compared to said first, second and third areas.

6. A iiuid-operated pumping unit, comprising: a pump adapted to be operated by a fiuid at a first pressure to discharge at a second pressure fiuid entering said pump at a third pressure; a cylinder; a piston in said cylinder; means for exposing at least a portion of one end of said piston to the first pressure; means for exposing at least a portion of the opposite end of said piston to the second pressure;` means for exposing at least a portion of one of vsaid'ends of said piston to the third pressure; and means for applying to at least v`acidosis a portion of one of said ends of said piston a fourth pressure balancing any netpressure force Vdifferential resulting from the application of the first, second and third pressures to said piston.

"7. In a device for absorbing pressure variations, the combination of: movable fluid separating ineans having first and 'third areas on one side thereof and having second and fourth areas on lthe opposite side thereof; means vfor applying -a first fluid pressure to said first area of lsaid fluid separating means; means Yfor applying a Asecond fluid pressure to said second area of said fluid separating means; vmeans for applying a third fluid pressure to said third areaof said lfluidseparating means; and Ameans for applying to said fourth area of said fluid Vseparating means a fourth lfluid pressure providing a vpressure force suilicient 'to balance the algebraic sum of the products of said first, second-and third areas and the first, second and third fluid pressures, respectively.

8. A device as defined in claim "Y wherein the means last defined includes a chamber which is adapted to contain a liquid and one wall of which is dened by said fourth area of said fluid separating means.

'9. In a shock absorber for use in a well pumping apparatus which includes a pump operable by an operating fluid to pump well fluid from the well to the surface as production fluid, the comblnation of movable fluid separating means having `a first pair of areas on one side thereof which are adapted to be exposed to the operating and well fluid pressures, respectively, and having a second pair of areas on the opposite side thereof one oi' which is adapted .to be exposed to the production fluid pressure.; and a chamber which is adapted to contain a liquid and one wall of which is defined by the other area of said second pair.

l0. In a shock absorber, the combination of: a cylinder having first and second ends; a tube axially aligned with said second end of said cylinder; means rigidly connecting said cylinder and said tube; a generally cup-shaped piston disposed in said cylinder and telescoped over said tube, said piston having a first surface Vexposed to fluid pressure in said tube so that fluid pressure in said tube tends to move said piston toward said first end of said cylinder, and said piston having a second surface exposed to fluid pressure vin said cylinder so that fluid pressure in said cylinder tends'to move said piston toward said second end of said cylinder; and fluid means for resiliently biasing said piston vtoward said second end of said cylinder, including a chamber which is adapted to contain a fluid and one wall of which is dened by a third surface of said piston so that fluid pressure in said chamber ytends to move said piston toward said second vend of said cylinder.

1l. In a shock absorber for use in connection with a hydraulically-actuated deep well pump having a column of operating liquid .at relatively high pressure and a column of pumped fluid at a relatively lower pressure, the combination of cylinder means; piston means in said cylinder means, having a first relatively small area facing in one direction, a second relatively large area facing in the other direction, and a third area of intermediate vsize facing in the same direction assaid first area, said first area being adapted to be constantlyexposed to the fluid pressure of said operating fluid column, said second area being adapted to be constantly exposed to the fluid pressure of said pumped fluid column, and said third area being adapted to be constantly exposed 12 to kthe `fluid 'pressure in the Well adjacent the pump, said areas 'being so related lin size -that said piston is substantially hydraulically balanced; and resilient kmeans engaging said piston means and adapted to dampen sudden fluid pressure surges vin one of said columns.

12. In a shock absorber fol` use in connection with a hydraulically-'actuated deep well pump having a `column of operating liquid at relatively high pressure and a column of pumped fluid at a relatively lower pressure, the combination of: cylinder means; piston means in said cylinder means, having a lfirst relatively small area facing in Vone direction, a second relatively large area facing in the Vother direction, and a third area of intermediate size facing in the same direction as said first area, said first area being adapted to ybe constantly exposed to the 'fluid pressure of said operating fluid column, said second area being adapted to be constantly exposed to the fluid pressure of said pumpedV fluid column, and said vthird area Abeing adapted to be constantly exposed A`to the v fluid pressure in the well adjacent the pump, said areas being so related in size that `said piston is substantially hydraulically balanced; and Ahydraulic means engaging said piston means and adapted to dampen sudden fluid pressure surges in one of said columns.

13. In a shock absorber for 'use in connection with a hydraulically-actuated deep well pump having a column of operating `liquid at relatively high pressure and a column of ypumped fluid at a relatively lower pressure, the combination i of: cylinder means; piston means in said cylinder means having a first relatively small area facing in one direction, a second relatively large area facing in the other direction, and a third area of intermediate size facing inthe samedirection 'as ysaid `rst area, said ilrst area being adapted to be constantly exposed to the fluid pressure of said operating fluid column, said second area being adapted to be constantly exposed to the fluid pressure of said pumped fluid column, and vsaid third area 'being adapted to be constantly exposed to the fluid pressure in the well adjacent the pump, said areas being so related in size that said piston is substantially hydraulically balanced; a stem connected to said piston 'means extending therefrom; land a substantially closed chamber filled with liquid into which said stem projects.

14. A'fn a shock labsorber for use in connection with a hydraulically-actuated vdeep Well pump having a column of operating liquid at relatively high pressure and a column of pumped fluid at a relatively lower pressure, the combination of: cylinder means; piston means in said cylinder means having a 'first relatively small area facing in one direction, a second relatively large area facing the other direction, and a third area of intermediate size facing in the same direction as said first area, said first area being adapted to be constantly exposed to the uid pressure of said operating fluid column, said second area being adapted to be constantly exposed to the fluid pressure of said pumped fluid column, and said third area being adapted to be constantly exposed 'to the rfluid ,pressure in the well adjacent the pump, said areas being so related in size that said piston is substantially hydraulically balanced; .a .stem of relatively small crossesectiona'l area compared with said first area and connected to said piston means and extending therefrom; and a substantially 15. In a, shock absorber for use in connection 5 with a hydraulically-actuated deep well pump having a column of operating liquid at relatively high pressure and a column of pumped uid at a relatively lower pressure, the combination of cylinder means, piston means in said cylinder means having a, lirst relatively small area facing in one direction, a second relatively large area facing the other direction, and a third area of intermediate size facing in the same direction as said first area, said rst area, being adapted to be constantly exposed to the fluid pressure of said operating fluid column, said second area being adapted to be constantly exposed to the iiuid pressure of said pumped iluid column, and said third area. being adapted to be constantly exposed to the iluid pressure in the well adjacent the pump, said areas being so related in size that said piston is substantially hydraulically balanced; a stem connected to said piston means and extending therefrom on 2 the same side of said piston means as said second area; and a substantially closed chamber lled with liquid into which said stem projects.

16. In a shock absorber for use in connection with a hydraulically-actuated deep well pump having a column of operating liquid at relatively high pressure and a column ofpumped uid at a relatively lower pressure, the combination of: cylinder means; piston means@ in said cylinder means having a first relativelyrk small area facing in one direction, a second relatively large area facing the other direction, and a third area of intermediate size facing in the same direci, tion. as said rst area, said first area being adapted to be constantly exposed to the fluid pressure of said operating fluid column, said second area being adapted to be constantly exposed to the fluid pressure of said pumped fluid column, and said third area being adapted to be constantly exposed to the fluid pressure in the well adjacent the pump, said areas being so related in size that said piston is substantially hydraulically balanced; a stem connected to said 1 piston means and extending therefrom; a substantially closed chamber iilled` with liquid into which said stem projects; and restricted .orice means communicating between the interior of said chamber and said pumpedfiuid column.

CLARENCE J. COBERLY.

References cited in the nie of this patent UNITED STATES PATENTS Number Name Date 2,576,923 Coberly Dec. 4, 1951 2,576,924 Coberly Dec. 4, 1951

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