US2576923A - Fluid operated pump with shock absorber - Google Patents

Description

Dec. 4, 1951 C. .,J. QOBERLY l FLUlD OPERATED PUMP WITH SHOCK ABSORBER 'Filed April s, 1948 3 Sheets-Sheet 2 Fig@ BY HLS ATTORNEYS. HAR/@s K/EcH, Fos'are da HAAP/afs Dec. 4, 1951 c. J. coBERLY 2,576,923

FLUlD OPERATEDVPUMP WITH SHOCK ABSORBER Filed April 5, 1948 3 Sheets-Sheet 5 K /Nl/ENTOR. CLA/z-:Nca d. COBERLY BY Hl` ATTORNEYS.

@A RR/s, K/EcH, Fos TER @HA/wels Y Patented Dec. 4, 1951 FLUID OPERATED PUMP WITH SHOCK ABSORBER Clarence J. Coberly, Los Angeles, Calif., assigner, by mesne assignments, to Dresser Equipment Company, Cleveland, Ohio, a corporation of Ohio Application April 3, 1948, Serial No. 18,768

23 Claims. 1

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

Fluid operated pumps are used extensively in theoil 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. Briefly, such a fluid 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, commonly referred to as power oil, to the pump and a production tubing for conveying oil discharged by the pump to the surface being connected to the motor and pump sections, respectively. The motor section of the pump includes a cylinder having a piston therein and includes a suitable valve mechanism for admitting the power oil in the power tubing alternately to opposite ends of the motor cylinder so as to reciprocate the piston therein, the power oil usually being clean crude oil. The pump section includes a cylinder having a piston therein which is connected to the motor piston, as by a piston rod, whereby the reciprocatory motion of the motor piston is communicated to the pump piston so that the latter draws iluid from the well and discharges it into the production tubing through suitable intake and exhaust valve mechanisms. Fluid operated pumps normally used in the oil industry are of the double acting type so that as well fluid is drawn into one end of 'the pump cylinder during a given stroke of the pump piston, well iluid drawn into the opposite end thereof during the preceding stroke is simultaneously discharged into the production tubing.

In order to prevent excessive wear and possible breakage of the various parts of a pump of this type. and in order to prevent damage to other components of the installation in which the pump is incorporated, it is essential to minimize any shock loads which may originate in the pump. Such 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 gas 'in 'the pump cylinder. The iluid entering the well casing from an adjacent oil producing formation may contain considerable quantities of natural gas ln solution or in suspension, or both, the amounts of natural gas 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 when the well is operated beyond its capacity so that air or gas is drawn into the pump cylinder.

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, the gas present in the well iluid may be liberated in the pump cylinder with the result that a quantty of liquid sufficient only to partially ll the pump cylinder is drawn thereinto, the balance of the pump cylinder being iilled with gas. Similarly, the pump cylinder may be partially filled with gas, at low pressure if the well is pumped beyond its capacity. In some instances the casing may be connected with. the vacuum line so the pressure on the gas may be less than atmospheric pressure. Also, in fields subjected to vacuum, air may be drawn in if the casing is left open. Consequently, when the direction of movement of the pump piston is reversed, the pump piston acts only on the gas or air in the pump cylinder for at least a portion of its stroke. Since the gas or air is highly compressible, it offers 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 normally employed because of the compressibility of the column of power oil in the power tubing and the expansibility of the power tubing. Such potential energy is released when the load on the pump pistons 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 be produced in the power oil and production fluid columns above the pump and may result vin abnormal stressing of and possible damage to other components of the system. If the well fluid being pumped contains a large percentage of water, which frequently is the case, shock loads originating in the pump may be particularly severe, the reason for this being that the compressibility of water is less than that of crude oil. Consequently, when water is present, the compressibility of the production uid column above the pump is materially reduced, as compared to the compressibility of a production iiuid column consisting of relatively pure crude oil, or a mixture of crude oil and gas, so that the amount of energy which it is capable of absorbing is materially decreased. Also, if air is drawn into the pump under shock loading conditions with water present, both mechanical failure and corrosion are greatly accelerated for two reasons: first, the presence of oxygen reduces the fatigue strength of the material; and, second, the high stress from shock loading increases the chemical attack at points of maximum stress.

A governor located in close proximity to the pump may be employed to reduce the rate of flow of power oil to the motor section of the pump in response to decreases in the load on the pump piston so as to reduce the piston speed which would otherwise be attained, an example of such a governor being disclosed in my Patent No. 2,311,157, issued February 16, 1943. However, due to the fact that such a governor begins to operate only after the condition which results in acceleration of the motor and pump pistons has already developed, there may be some lag in its operation. Consequently, even if a governor is employed, shock loads of undesirably large magnitude may be produced, although such shock loads are, of course, greatly reduced as a result of the use of the governor.

Even when a fluid operated pump of the type disclosed in my Patent No. 2,134,174, for example, is operating under normal conditions, i. e., when little or no gas or air is present in the well fluid, pressure pulsations occur in both the power oil and production uid columns due to the fact that the motor and pump pistons stop momentarily at the ends of their stroke. 'Ihis causes an increase in the pressure of the power oil and a decrease in the presence of the production iiuid. The amount of dwell at the ends of the stroke may be controlled with an engine valve of the type disclosed in my Patent No. 2,134,174, it being desirable to have sulcient 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 iiuid columns result, and if it is too small, serious pressure pulsations in the production fluid column results. In practice, it is diicult and, in many instances, impossible to eliminate such pressure pulsations regulation of the time allowed for the pump valve to seat. The magnitude of such pressure pulsations is low when the pump is operated at moderate speeds and when the pump cylinder fills properly. However, at high pump speeds, such pressure pulsations may be sufficiently large to cause serious diiculties. Severe stresses may be developed in various components of the installation by the pulsations if the frequency of the ricprocatory motion of the motor and pump pistons coincides with either the natural frequency of oscillation or one of the harmonics of either the power oil or the production fluid columns f pump valves.

above the pump, i. e., if the frequency of the pressure pulsations developed in the columns as a result of the reciprocatory motion of the motor and pump pistons coincides with either the natural frequency or one of the harmonics of one of the columns. These columns are only moderately 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 fluid columns are usually relatively low/ as compared to the frequency of 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 of the columns. However, it is virtually impossible to select an operating speed for the pump which avoids both the natural 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 makes it difficult to avoid both the natural frequency and all of the harmonies of the production fluid column in particular is that the natural frequency of this column varies with variations in the proportions of gas, oil and water in the production fluid. Consequently, since resonant operating conditions cannot be avoided readily by a selection of a suitable operating speed for the pump, it is f desirable to reduce the magnitude of the pressure surges resulting from the reciprocatory nature of the operation of the pump so as to avoid producing standing pressure waves of excessive magnitude.

In fluid operated pump installations of the type shown in my Patent No. 2,134,174, the power oil and production fluid columns are semiclosed systems and do not freely communicate with each other in both directions because the uid operated pump is interposed between them. The direction and amount of communication possible depends upon the positions of the engine and With closed columns each terminating in a valve serious "water hammer may result from sudden closing of the valve with high fluid velocities. In al1 cases of normal operation and some cases of shock resulting from malfunctioning of the pump valves or improper fill# ing of the pump cylinder, the pressure surges in the two columns are out of phase and may be cancelled out or greatly reduced by providing pressure communication between the columns, which is an important object of my invention.

Another` object of the invention is to provide a shock absorber which is exposed to the uid pressures obtaining in both the power tubing and the production tubing at points in close proximity to the pump so that pressure surges originating in the pump are absorbed substantially instantaneously.

More specifically, an object is to 'provide a shock absorber which includes a movable fluid separating means, such as a piston, for example, having a pair of opposed surfaces one of which is exposed to fluid pressure in the power tubing and the other of which is exposed to fluid pressure in the production tubing.

An important object is to provide a shock absorbet wherein the areas of the two opposed surfaces of the piston and the fluid pressures normally obtaining in the power and production tubings are so related that the piston is normally substantially balanced whereby any variations in the relative pressures obtaining in the two tubings will result in movement of the piston.

Another object is to provide such a shock absorber which includes resilient means acting on the piston for absorbing any pressure surges tending to move the piston so as to avoid developing shock loads in the system.

A further object is to provide a shock absorber wherein the resilient means comprises one or more compression springs which may engage either or both ends of the piston.

Still another object of the invention is to provide a shock absorber wherein the piston is reciprocable longitudinally of a cylinder which communicates with the production tubing, and is reciprocable longitudinally of a tube which communicates with the power tubing. A related object is to provide a shock absorber of this character having a generally cup-shaped piston which is disposed in the cylinder and which is telescoped over the tube.

Other objects oi' the invention are to provide a shock absorber which may be connected directly to a pump with which it is used, 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 evident, may be attained through the utilization of the exemplary embodiments which are illustrated in the accompanying drawings and which are described in detail hereinafter. Referring to the drawings:

Fig. 1 is a utility view on a reduced scale showing, a vertical section, 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 and a lower portion of a uid operated pump to which the shock absorber is connected;

Fig. 3 is an enlarged vertical sectional viewv which is taken along the broken line 3-3 of Fig. 1 and which shows an intermediate portion of the shock absorber, Fig. 3 being a downward extension of Fig. 2;

Fig. 4 is an enlarged vertical sectional view which is taken along the broken line 4-4 of Fig. 1 and which shows the lower portion of the shock absorber, Fig 4 being a downward extension of Fig. 3;

Figs. 5 and 6 are transverse sectional views which are taken along the broken lines 5-5 and 5 8, respectively, of Figs. 2 and 4. respectively;

Figs. 'l and 8 are vertical sectional views which are similar to Figs. 2, 3 and 4 but which show another embodiment of the invention;

Figs. 9 and 10 are vertical sectional views which are also similar to Figs. 2, 3 and 4 but which show still another embodiment of the invention; and l Fig. 11 is a graph illustrating the operation of my shock absorber.

Referring particularly to Fig. 1 in the drawings, I show a well casing II which extends into an oil producing formation I2 of a well, the lower end of the casing being perforated. as indicated at I3, so that well fluid from the formation may flow into the casing. A production tubing I4 extends downwardly through the casing II into a body I5 of well fluid in the lower portion thereof, the lower end of the production tubing being equipped with a tapered seat I5 which is adapted to receive and support an inlet fitting I'I. A uld operated pump I8 is disposed in the production tubing I4 and is connected to the lower end of a power tubing I9 for conveying power oil to the pump. the power tubing extending downwardly through the production tubing. A shock absorber 20 of the invention is interposed between theinlet fitting I1 and the pump I3 in the particular construction illustrated in the drawings, the shock absorber being connected to the inlet fitting at its lower end and to the pump at its upper end.

The structural details of the fluid operated pump I3 form no part of the present invention and the pump is not shown in detail In the drawings. The pump I3 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. In general, the pump I8. as best shown in Fig. 1 of the drawings. includes a motor piston 2| which is reciprocable in a motor cylinder 22, and includes a pump piston 23 which is reciprocable in a pump cylinder 24, the motor and pump pistons being connected by a rod 25. Connected to and extending upwardly from the motor piston 2| is an upper rod 26, and connected to and -extending downwardly from the pump piston 23 is a lower rod 21, the latter being reciprocable in a tube 28 which is threaded into a bore 29 in a fitting 30 at the lower end of the pump I3, as best shown in Fig. 2 of the drawings. The pump I8 is provided with a continuous passage 3I which communicates at its upper end with the power tubing I9 and which communicates at its lower end with the shock absorber 20 as will be discussed in more detail hereinafter, the passage 3| extending through the upper rod 26, the motor piston 2I, the intermediate rod 25, the pump piston 23 and the lower rod 21.

The general operation of the pump I8 is well known in the art, being described in detail in my aforesaid Patent No. 2,134,174, and needs be described only brieiiy herein. Power oil, such as clean crude oil, for example, flows downwardly through the power tubing I9 to the pump I8 to operate same. Such power oil is introduced alternately into opposite ends of the motor cylinder 22 by a suitable valve mechanism (not shown) so as to reciprocate the motor piston 2I, the reciprocatory motion of the motor piston beingcommunicated to the pump piston 23 by the intermediate rod 25. Well iiuid from the body I5 is introduced alternately into opposite ends of the pump cylinder 24 by a suitable valve mechanism (not shown) and is discharged into the production tubing I4 as production iiuid by the pump piston 23, the production fluid subsequently ilowing upwardly through the tubing I4 to the surface. As will be discussed in more detail hereinafter, the well iiuid enters the pump I8 by way of the inlet fitting Il and the shock absorber 20, the tting 30 at the lower end of the pump being provided with a plurality of passages 32 through which the well fluid may flow from the shock absorber into the pump, as best shown in Fig. 2 of the drawings.

Referring particularly to Figs. 2, 3 and 4 of the drawings, the shock absorber 20 includes a tubular housing 33 which is internally threaded at its ends, the inlet fitting I'I being threaded into the lower end of the housing and a tting 3.4

being threaded into the upper end thereof. The inlet iitting I1 terminates at its lower end ina irusto-conical portion 35 which is insertable into the tapered seat I5 at the lower end of the production tubing I4, this portion of the inlet tting carrying a sealing ring 39 which is adapted to engage the tapered seat so as to provide a fiuidtight seal between the well uid in the casing Ii and the uid in the production tubing. The fitting 34 at the upper end of the tubular housing 33 is adapted to be threadedly connected to the fitting 39 at the lower end of, the pump I8 in any suitable manner.

As best shown in Figs. 3 and 4 of the drawings, the inlet tting Ill is provided with a cylindrical extension 31 which projects into the tubular housing 33 and which is threaded into the lower end of a cylinder 33 having a generally cup-shaped piston 33 therein, the external di-` ameter of the cylinder 3B being less than the internal diameter of the tubular housing 33 to provide an annular space all therebetween for a purpose to be discussed hereinafter. In theparticular construction illustrated, the cylinder 38 is open at its upper end so that the piston 39 mayl project therefrom as it moves upwardly in the cylinder. The piston 39 derives its cup-like shape from an axial bore 3i therein which receives a tube 42, the latter being axially aligned with the cylinder 38 and extending into the upper end thereof in the particular construction illustrated. lThefexternal diameter of the tube 42 is less than the internal diameter of the tubular housing 33 to provide an annular space 44 there'- between and the upper end of the tube 42 is threaded into a bore 43 in the fitting 34 at the upper end of the tubular housing, the bore y43 being in iiuid communication with the bore 29 in the iitting at the lower end of the pump I9, as best shown in Fig. 2 of the drawings. The piston 39 is provided with annular grooves 45 and 45 therein for sealing rings 41 and 48 which respectively provide uid-tight seals between the piston and the cylinder 38 and between the piston and the tube 42. Preferably, the bore 4I in the piston 39 is enlarged throughout a substantial portion of its length to reduce the area of sliding contact between the piston and the tube 42, such enlargement of the bore in the piston providing an annular shoulder 49 adjacent the upper end of the bore.

In the embodiment of the invention illustrated in Figs. 2 tov6 of the drawings, the piston 39 is biased upwardly by a resilient means comprising a compression spring 50 which is seated against the lower end of the piston and against the upper end of the cylindrical extension 31 of the inlet fitting I1. depending stem 5I on the piston 39 which is provided with a tapered portion 52 at its lower end, the tapered portion of the stem being insertable into a bored recess 53 in the cylindrical extension 31 of the inlet ttng I1 as the piston moves into its lowermost position. As will be discussed in more detail hereinafter, the tapered portion 52 of the stem 5l and the recess 53 provide a dashpot means for decelerating the piston 39 as it approaches the lower limit of its travel.

The shock absorber 20 is also provided with dashpot means, indicated generally by the numeral 54, for decelerating the piston 39 as it approaches the upper limit of its travel. As best shownin Figs. 2 and 3 of the drawings.. the piston 39 is provided with a tapered portion 55 at its upper end which is insertable into a recess 55 The spring 50encirc1es aformed by counterboring a downward extension 51 of the i'ltting 34, the recess 56 being formed at its lower end with a counterbore 58 into which the tapered portion 55 of the piston is insertable. It will be apparent that as the piston 39 approaches the upper limit of its travel, the tapered portion 55 of the piston will enter the counterbore 58 to restrict now out of the recess E56, thus decelerating the piston.

As previously indicated, the piston 39 is exposed to various uid pressures obtaining in the system and the manner in which this is accomplished will now be described. As best shown in Fig. 4 of the drawings, the inlet fitting i1 is provided with an axial passage 59 therein which communicates at its lower end with the body Iii of oil or other well fluid in the casing ii, and which communicates at its upper end with a plurality of radial passages 60. The latter communicate with the annular space 40 between the tubular housing 33 and the cylinder 38 so that well fluid may flow upwardly through the passage 59, the passages B0 and the annular space @il into the annular space 44 between the housing 33 and the tube 42. From the space 44 the well fluid may ow upwardly into the pump I8 through a plurality of passages 6I in the fitting 34 which communicate with the passages 32 in the tting 30. As best shown in Fig. 3 of the drawings, the pressure of the well uid is applied to the upper end of the piston 39, the eiective area of the upper end of the piston being equal to the difference between the cross-sectional area of the piston and the cross-sectional area of the tube 42.

The pressure of the production iiuid discharged into the tubing I4 by the pump I8 is communicated to the interior of the cylinder 39 through a plurality of passages 55 in the inlet fitting I1, the passages communicating at their lower ends with the interior of the production tubing above the sealing ring 36 carried by the inlet tting, and communicating at their upper ends with the recess 53 in the cylindrical extension 31 of the inlet fitting. It will be noted that the fluid pressure obtaining in the production tubing I4 tends to move the piston 39 upwardly in the cylinder 38 and is applied to a transverse area equal to the cross-sectional area of the piston.

Since, as previously discussed, the bore I3 in the iitting 34 at the upper end of the shock absorber 20 communicates with the bore 29 in the fitting 30 at the lower end of the pump I3. power oil from the tubing I9 may enter the tube 42 in the shock absorber by way of the passage 3| through the motor and pump pistons 2i and 23 and the rods 25, 29 and 21. Consequently, the iiuid pressure obtaining in the power tubing I9 is applied to the bottom wall of the bore 4I in the piston 29 and tends to move the piston dovmwardly in the cylinder 38. It will be noted that the effective transverse area to which the uid pressure obtaining in the power tubing i9 is applied is equal to the cross-sectional area of the tube 42, part of the downward force resulting from the application of such fluid pressure to the bottom wall of the bore 4I being offset by the application of this same pressure to the shoulder 49 at the upper end of the enlarged portion of the bore 4I.

Thus, it will be apparent that the piston 39 is subjected to a downward force equal to the product of the iiuid pressure obtaining in the well casing II and an area equal to the difference annees between the cross-sectional areas of the piston and the tube 42, a downward force equal to the product of the fluid pressure obtaining in the power tubing I9 and an area equal to the external cross-sectional area ofthe tube 42, an upward force equal to the product of the fluid pressure obtaining inthe production tubing I4 and the cross-sectional area of the piston. and an upward force equal to the force exerted by the spring 50. It will be noted that the downward force produced by the application of the fluid pressure obtaining in the well casing II to the piston 39 may be relatively small, particularly if the level of the body I5 of well fluid is low. Normally, the well fluid pressure applied to the piston 39 is substantially equal to atmospheric pressure. On the other hand. the fluid pressures obtaining in the production tubing I4 and the power tubing I9 may be of the order of magnitude of' several thousand pounds per square inch.

The areas of the piston 39 exposed to the fluid pressures obtaining in the well casing Il, the production tubing I4 and the power tubing I9 and the force applied to the piston by the spring 50 are so related that the piston is balanced when normal operating conditions for the pump I3 prevail, i. e., the summation of the upward and downward forces applied to the piston is equal to zero. For example. if the fluid pressure obtaining in the production tubing I4 is approximately one-half that obtaining in the power tubing I9, the area of the piston exposed to vfluid pressure obtaining in the production tubing will be approximately twice that exposed to fluid pressure obtaining in the power tubing, the area exposed to fluid pressure obtaining in the casing II being relatively unimportant since the well fluid pressure is normally substantially equal to atmospheric pressure as previously discussed. Thus, the areas exposed to the fluid pressures obtaining in the power and production tubings and the spring force are the principal factors to be taken in to consideration in balancing the piston 33 for normal conditions of operation. If the relative fluid pressures obtaining in the power and production tubings in particular vary, the piston 39 becomes unbalanced and moves either upwardly or downwardly in the cylinder 38, depending upon the direction of unbalance. Such variations in the relative fluid pressures may arise from various sources. For example, if air or gas is present in the pump cylinder 24, the pump piston 23 may, as previously discussed,`accelerate to an excessive speed so that a' pressure surge in the production tubing I4 may result when it strikes solid well fluid. Also, pressure pulsations may be produced in the fluids in the production tubing I4 and power tubing I9 due to the reciprocatory motion of the motor and pump pistons 2I and 23 as previously discussed. Pressure surges resulting from the foregoing or other causes may vary the relative uid pressures obtaining in the production tubing I4 and the power tubing I9 in particular so that an unbalanced force acting either upwardly or downwardly as the case may be is applied to the piston 39. If, for example, the unbalanced force acts downwardly, the energy producing the force is absorbed by compression of the spring 50 and by compression of the production fluid in the cylinder 38 and the production tubing I4. If the unbalanced force acts upwardly, the energy producing same is absorbed by compression of the i operating fluid in the tube 42 and the power tubing I9. Thus, pressure surges whichmight l0 otherwise produce hydraulic shock loads having detrimental effects are absorbed.

Considering in more detail the manner in which pressure pulsations resulting from the reciprocatory motion of the motor and pump pistons 2| and 23 are absorbed, and referring particularly to Fig. 11 of the drawings, the numerals 15 and 16 indicate curves showing, respectively, typical pressure pulsations encountered in the power oil and production fluid columns when a pump such as the pump I3 is used without the shock absorber 20. It will be noted that the power oil pressure rises at the ends of the stroke of the motor and pump pistons 2| and 23 (see curve 15) and that the pump discharge pressure or production fluid pressure drops at' the same time (see curve 16), the pressure pulsations in the two columns being of approximately the same magnitude and of opposite sign. The rise in pressure in the power tubing I9 and the drop in pressure in the production tubing I4 cause the piston 39 to move down against the force of the spring 50, such movement reducing the pressure in the power oil tubing and increasing the pressure in the production tubing. The resultant pressure in the two columns is approximately as indicated by the curve 11 in Fig. 11. the curve 11 having been obtained by adding the curves 15 and 16 graphically. Thus, it will be apparent that my shock absorber causes the rise in power oil pressure and the drop in production fluid pressure to cancel out, which is an important feature of the invention.

The passages providing fluid communication between the production tubing I4 and the interior of the cylinder 38 are preferably relatively small so that now from the production tubing into the cylinder and vice versa as the piston 39 moves upward and downward in the cylinder is throttled to some extent. Such throttling of flow between the production tubing I4 and the interior of the cylinder 38 dampens oscillations of the piston 39 which might otherwise result, this being an important feature of the invention.

As previously mentioned, the tapered portion 52 of the stem 5I on the piston and the recess 53 in the cylindrical extension 31 of the inlet fitting I1 provide a. dash-pot means for decelerating the piston in the event that it approaches the lower limit of its travel at a high speed under the influence of a large unbalanced force acting in the downward direction. It will be noted that as the tapered portion 52 of the stem 5I enters the recess 53, it reduces the area of the passage through which fluid in the cylinder 38 may escape into the passages 65 leading to the production tubing I4. Consequently, a large decelerating force is applied to the piston 39. It will be noted that the lower end of the stem 5I on the piston 39 is adapted to seat in the bottom of the recess 53 so that it serves as a stop tolimit downward movement of the piston. The dash-pot means 54 operates in a similar manner to decelerate the piston 39 as it approaches the upper end of its travel.

The embodiment of the invention illustrated in Figs. 7 and 8 of the drawings is substantially identical to that illustrated in Figs. 2 to 6 except that a resilient means comprising a compression spring 10 is substituted for the spring 59, the spring 1I) being seated against the upper end of the piston 39 and against the upper end wall of the recess 56 in the downward extension 51 of the fitting 34. The embodiment illustrated ln` l1 Figs. 9 and l0 of the drawings is essentially a combination o f the embodiment illustrated in Figs. 7 and 8 with that illustrated in Figs. 2 to 6, both the spring 50 and the spring 10 being employed. As is the case with the embodiment illustrated in Figs. 2 to 6 of the drawings, in the embodiments illustrated in Figs. 'I to 10, the areas of the respective pistons 39 which are exposed to the fluid pressures obtaining in the system and the forces developed by the springs 50 and 10 are so related that the pistons are normally balanced. The operatiopof the embodiments illustrated in Figs. '7 to liiof the drawings will be apparent from the previous description of the operation of the embodiment illustrated in Figs. 2 to 6 and will not be described in detail.

Although I have disclosed several exemplary embodiments of my invention herein for purposes of illustration, I do not intend to be vlimited specifically thereto since various changes, modications and substitutions may be incorporated in the embodiments disclosed without necessarily departing from the spirit of the invention, and I hereby reserve the right to all such 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:

1. In a fiuid operated pumping unit, the combination of a source of a first fiuid at a substantially constant pressure level; a receiver for a second iiuid to be pumped; a. pump adapted to be operated by the first fiuid to pump the second fluid; a. shock absorber connected to said pump and having movable fiuid separating means therein; first passage means communicating between said source and said shock absorber for admitting the first fiuid into said shock absorber on one side of said fiuid separating means; and

second passage means communicating between said receiver and said shock absorber for admitting the second fiuid into said shock absorber on the opposite side of said fluid separating means.

2. A pumping unit as set forth in claim 1 wherein the product of the area of said one side of said fluid separating means and the pressure of the first fluid substantially equals the product of the area of said opposite side of said fluid separating means and the pressure of the second fluid.

3. A fiuid operated pumping and shock-absorbing unit, comprising: a source of a first uid at a substantially constant pressure level; a receiver for a second fiuid to be pumped; a pump adapted to be operated by the first fluid to pump the second fiuid; a cylinder connected to said pump; a piston in said cylinder; means communicating between said source and said cylinder for exposing at least a portion of one side of said piston to the pressure of the first fluid; and means communicating between said receiver and said cylinder for exposing the opposite side of said piston to the pressure of the second fluid.

4. A fluid operated pumping and shock-absorbing unit according to claim 3 including resilient means for urging said piston toward one end of said cylinder.

5. In an apparatus for pumping fiuid from a well, the combination of: a fiuid 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 production fluid discharged thereby;

and a shock absorber connected to said pump, said shock absorber including movable fiuid separating means having opposed first and second surfaces, including means for exposing said first surface of said fiuid separating means to fiuid pressure obtaining in said first tubing, and including means for exposing said second surface of said fiuid separating means to fiuid pressure obtaining in said second tubing.

6. In a shock absorber for use in a well pumping apparatus which includes a fiuid operated pump having first and second tubings connected thereto, the first tubing being adapted to convey operating fiuid to the pump to operate same and the second tubing being adapted to convey from the pump production fiuid discharged therebypthe combination of: movable fiuid separating means having opposed iirst and second surfaces; means for exposing said first surface of said fluid separating means to fiuid pressure obtaining in the first tubing; and means for exposing said second surface of said fiuid separating means to fiuid pressure obtaining in the second tubing.

7. In a shock absorber for use in a well pumping apparatus which includes a iiuid operated pump having rst and second tubings connected thereto, the first tubing being adapted to convey operating fiuid to the pump to operate same and the second tubing being adapted to convey from the pump production fiuid discharged thereby, the combination of a cylinder; a. piston disposed in and reciprocable longitudinally of said cylinder, said piston having opposed, transverse first and second surfaces; means for exposing said first surface of said piston to fiuid pressure obtaining in the first tubing; and means for exposing said second surface of said piston to fiuid pressure obtaining in the second tubing.

8. A shock absorber according to claim 7 including resilient means for biasing said piston toward one end of said cylinder.

9. In a shock absorber for use in a well pumping apparatus. which includes a fluid operated pump having first and second tubings connected thereto, the iirst tubing being adapted to convey operating fiuid to the pump to operate same and the second tubing being adapted to convey from the pump production fiuid discharged thereby, the combination of: a cylinder having rst and second ends; a piston disposed in and reciprocable longitudinally of said cylinder, said piston having opposed, transverse first and second surfaces; means for exposing said rst surface of said piston to fluid pressure obtaining in the first tubing whereby the fluid pressure obtaining in the first tubing tends to move said piston toward said first end of said cylinder; means for exposing said second surface of said piston to fiuid pressure obtaining in the second tubing so that the fiuid pressure obtaining in the second tubing tends to move said piston toward said second end of said cylinder; andresilient means for biasing said piston toward said first end of said cylinder.

10. In a shock absorber for use in a well pumping apparatus which includes a fluid 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 vproduction fiuid discharged thereby. the combination of: a cylinder having first and second ends; a piston disposed in and reciprocable longitudinally of said cylinder, said piston having opposed, transverse first and second surfaces; means for exposing said first surface of said piston to fluid pressure obtaining in the ilrst tubing whereby fluid' pressure obtaining in the flrst tubing tends to move said piston toward said first end of said cylinder; means for exposing said second surface of said piston to fluid pressure obtaining in the second tubing so that the fluid pressure obtaining in the second tubing tends to move said piston toward said second end of said cylinder; and resilient means for biasing said piston toward said second end of said cylinder.

11. In a shock absorber for use in a well pumping apparatus which includes a fluid operated pump having flrst and second tubings connected thereto, thef'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 production fluid discharged thereby, the combination of: a cylinder having first and second ends; a piston disposed irl/and reciprocable longitudinally of said cylinder, said piston having opposed, transverse flrst and second surfaces; means for exposing said first surface of said piston to fluid pressure obtaining in the first tubing whereby the fluid pressure obtaining in the first tubing tends to move said piston toward said first end of said cylinder; means for exposing said second surface of said piston to fluid pressure obtaining in the second tubing so that the fluid pressure obtaining in the second tubing tends to move said piston toward said second end of said cylinder; first resilient means for biasing said piston toward said first end of said cylinder; and second resilient means for biasing said piston toward said second end of said cylinder.

12. In a shock absorber for use in a pumping apparatus which is adapted to be set in a well and which includes a fluid operated pump having flrst and second tubings connectedthereto, 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 production fluid discharged thereby, the combination of a cylinder; a piston disposed in and reciprocable longitudinally of said cylinder, said piston having rst and third transverse surfaces on one side thereof and having a second transverse surface on the opposite side thereof;

means for exposing said firstl surface of said piston to fluid pressure obtaining in the first tubing; means for exposing said second surface of said piston to fluid pressure obtaining in the second tubing; and means for exposing said third surface of said piston to fluid pressure obtaining in the well substantially at the level of the pump.

13. A shock absorber as defined in claim including resilient means for biasing said piston toward one end of said cylinder.

14. In a shock absorber, the combination of z a cylinder; an imperforate tube axially aligned with said cylinder; a piston disposed in said cylinder and reciprocable longitudinally of said cylinder and said tube, said piston having a ilrst surface exposed to fluid pressure in said tube and having a second surface exposed to fluid pressure in said cylinder; sealing means disposed between said piston and said cylinder and providing a fluid tight seal therebetween; and seaiing means disposed between said piston and said tube and providing a fluid tight seal therebetween.

15. A shock absorber according to claim 11 including resilient means for biasing said piston toward one end of said cylinder.

16. In a shock absorber, the combination of a cylinder having first and second ends; an imperforate tube axially aligned with said second end of said cylinder; means rigidly connecting said cylinder and said tube; a generally cupshaped piston disposed in said cylinder and telescoped over said tube, said piston having a first surface exposed 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 in said cylinder so that fluid pressure in said cylinder tends to move said piston toward said second end of said cylinder; sealing means disposed between said piston and said cylinder and providing a fluid tight seal therebetween; sealing means disposed between said piston and said tube and providing a fluid tight seal therebetween; and resilient means for biasing said piston toward said first end of said cylinder.

1'7. In a shock absorber, the combination of: a cylinder having first and second ends; an imperforate tube axially aligned with said second end of said cylinder; means rigidly connecting said cylinder and said tube; a generally cupshaped piston disposed in said cylinder and telescoped over said tube, said piston having a first surface exposed 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 in said cylinder so that fluid pressure in said cylinder tends to move said piston toward said second end of said cylinder; sealing means disposed between said piston and said cylinder and providing a fluid tight seal therebetween; sealing means disposed between said piston and said tube and providing a fluid tight seal therebetween; and resilient means for biasing said piston toward said second end of said cylinder.

18. In a shock absorber, the combination of: a cylinder having first and second ends; an imperforate 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 exposed 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 in said cylinder so that fluid pressure in said cylinder tends to move said piston toward said second end of said cylinder; sealing means disposed between said piston and said cylinder and providing a fluid-tight seal therebetween; sealing means disposed between said piston and said tube and providing a fluid-tight seal therebetween; first resilient means for biasing said piston toward said flrst end of said cylinder; and second resilient means for biasing said piston toward said second end of said cylinder.

19. A shock absorber as set forth in claim 7 including dash-pot means for decelerating said piston at each end of its travel.

- 20. A shock absorber as set forth in claim 'I wherein the last-mentioned means provides throttled fluid communication between said cylinder and the second tubing,

2l. A shock absorber according to claim 6 including resilient means for automatically bal- 15 ancing any difference between the uid pressure forces applied to said movable iluid separating means by the uid pressures obtaining in the rst and second tubings.

22. A shock absorber according to claim 21 wherein said resilient means includes a compression spring seated against said fluid separating means.

2,3. A shock absorber according to claim 12 including means for resiliently balancing any net pressure force applied to said piston by the uid pressures obtaining in the rst and second tubings and in the well.

CLARENCE J. COBERLY.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 1,614,657 Cotton Jan. 18, 1927 1,809,084 VanBerkel et a1 June 9, 1931 2,134,174 Coberly Oct. 25, 1988 2,267,902 Eddins Dec. 30, 1941 2,311,157 Coberly Feb. 16, 1943 2,340,943 Downs Feb. 8, 1944

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