US2132738A

US2132738A - Gas-lift pump

Info

Publication number: US2132738A
Application number: US49942A
Authority: US
Inventors: Granville S Knox
Original assignee: B E AHLPORT
Current assignee: B E AHLPORT
Priority date: 1935-11-15
Filing date: 1935-11-15
Publication date: 1938-10-11
Anticipated expiration: 1955-10-11

Description

G. S. KNOX GAS LIFT PUMP Oct. 11, 1938.

Filed Nov. 15, 1935 2 Sheets-Sheet 1 INVENTOR.

X ATTORNEYS Oct. 11, 1938. s. KNOX GAS LIFT PUMP Filed Nov. 15, 1935 '2 Sheets-Sheet 2 Patented a. 11, 1938 PATENT orrlcr.

GAS-LIFT PUIHP Granville S. Knox, Los Angeles, Calif., assignor of one-half to B. E. Ahlport, La Canada, Calif.

Application November 15, 1935, Serial No. 49,942

37 Claims.

This invention relates to pressure actuated pumps used in lifting liquids from" wells, and more particularly to pumps using natural gas, compressed air, steam or other gaseous substance under pressure as the actuating medium.

An object of the invention isv to provide a durable mechanism for lifting liquids containing abrasive or corrosive matter out of wells without the use of reciprocatingplungers or sucker rods which would be damaged by the abrasive or corrosive elements in the liquid.

Another object is to provide a method of producing oil from oil wells, which method will effect an economy in the amount of natural gas produced with the oil in order to conserve the gas, thereby maintaining the pressure in the formation and extending the period of economical oil production.

Another object is to provide a pressure actu- I ated mechanism for lifting liquid from wells that responds to varying well conditions to automatically so regulate the rate at which liquid is lifted as to cause the mechanism to operate at best efliclency at all times.

Another object is to provide a small compact gas-lift pump unit which may be readily inserted in and removed from standard size well tubing or casing.

Still another object is. to provide a gas-lift pumping unit which comprises few, simple and compact parts which cannot easily get out of,

order, thus increasin the efiiciency of the unit and reducing the cost of manufacturing it and of maintaining it in operating condition.

Other more specific objects and features of the invention will be apparent from the detailed description with reference to the drawings which follow.

Oil has been usually lifted from wells by reciprocating plunger pumps located deep in the well and actuated by a string of sucker rods extending up through the well to the surface. Such pumps have given satisfactory results in shallow wells producing clean oil, but they are a constant source of trouble in deep wells, wells with crooked bores and wells producing abrasive and corrosive elements with the oil. In deep wells the sucker rod string is greatly over-loaded and is a constant source of trouble due to the stretching and breaking of the rods. In wellshaving crooked bores excessive wear takes plate on both the sucker rods and well tubing, necessitating costly replacement. In wells containing abrasive or corrosive elements, or both, the pump plunger and barrel quickly wear out or the close fitting They have been fairly satisfactory in erable water is present with the oil, the use of ordinary gas-lift methods causes a tight oil water emulsion which requires special and somewhat expensive methods of treatment to obtain a separation of the oil and water at the surface.

A gas-lift pump in accordance with my present invention operates without sliding plungers or barrels and without any movable mechanical elements connecting the pump in the well to the surface. Furthermore, although my pump employs gas pressure for its operation, the gas is not mixed with the liquid pumped and where the liquid contains oil and water it does not emulsify the oil and water. Furthermore, my pump. operates as a pressure displacement pump in much the same manner as a plunger displacement pump and it is not necessary to satisfactory operation to have a high liquid level in the well. As a result, my pump combines to a large extent the desirable features of the ordinary gas-lift pump and the reciprocating plunger pump while avoiding many of the undesirable features of both.

In the drawings:

Fig. 1 is a schematic diagram showing one pumping unit in accordance with my invention installed in a well;

Flg. 2 is a schematic diagram of a different form of unit in accordance with the invention;

Fig. 3 is a schematic diagram illustrating one method of employing the units shown in Figs. 1 and 2 in a well;

Fig. 4 is a schematic diagram illustrating another method of employing my unit in a well;

Fig. 5 is a schematic diagram illustrating still another method of employing my unit in a well;

Fig. 6 is a schematic diagram of a modification of the unit shown in Fig. 1;

Figs. 7 and 8 are vertical sectional views showing in detail the actual construction that may be employed in a unit of the type disclosed schematically in Fig. 1; a

Fig. 9 is a vertical sectional view showing the actual construction that may be employed in a unit of the type shown schematically in Fig. 2; and

Fig. 10 is a sectional detail view of a needle valve that may be employed with a unit in accordance with my invention in some installations.

Referring to Fig. 1, a pumping unit I, in accordance with the invention, is shown inserted upon tubing string positioned in a Well casing 4. The portion 5 of the tubing string above the unit I extends to the surface and connects at the surface to a discharge pipe 6 adapted to rereceive gas and liquid and discharge them at low pressure. Thus the pipe 6 may discharge into an open receptacle or it might be connected to a suction pump which maintains a pressure less than atmospheric in the pipe 6. That portion 1 of the tubing extending below the unit I extends below the level of the fluid in the casing 4, which fluid is to be pumped. The upper end of the cas ving 4 is preferably closed to retain gas pressure therein. This gas pressure may result from the natural gas production of the well or it. may be artificially created by pumping gas into the casing as through a pipe 8 connecting to the casing at the surface.

The unit I comprises a body member of lateral dimensions less than the inner diameter of the casing 4 which defines therewithin a passage 9 communicating through a standing valve I 0 with the tubing 1 below the unit. The upper end of the passage 9 communicates through a passage 35 with a chamber II which communicates through a port I2 with a passage I3 which-communicates with a passage I4, the latter opening into the tubing 5 above the unit.

The passage 35 is adapted to be closed by a valve I5. Thus the lower edge of passage 35 constitutes a valve seat against which the valve I5 is constantly urged by a spring I6. To open the valve against the force exerted by the spring IS, a push rod I1 is provided which projects through the passage 35 and is attached at its upper end to the lower end wall of a bellows I8, the upper end of which is anchored to and seals with the upper end wall of chamber II. The interior of the bellows I8 communicates through a nozzle I9 with a passage 20 which interconnects a chamber 2I and a chamber 22. Chamber 2I communicates through a port 23 with the exterior of the unit I, and chamber 22 communicates through a port 24 with the passage I 4 which is in direct communication with the tubing 5. It will be observed, therefore, that the exterior of the bellows I8 is exposed to the pressure of the fluid in the chamber II and the interior of the bellows I8 is exposed to the pressure existent in the passage 20. The upper endof the passage 20 is normally closed by a standing valve 25 and the passage 24 is adapted to be closed by a valve 26 which is urged against a seat .at the lower end of the passage 24 by a spring 21. To open the valve 26 a push rod 28 is provided, extending down through the passage 24 and secured thereabove to the

end walls

29 and 30, respectively, of a pair of bellows 3I and 32, respectively. The opposite ends of the bellows 3I and 32 are anchored to a rigid tubular member 33.which is anchored to the body member I andforms with the bellows 3I and 32 a closed chamber which may be evacuated or may contain some gas at relatively low pressure.

The unit described functions as follows: Assume that the casing 4 contains liquid, the surface of which is only a relatively slight distance below the unit I and contains gas above the liquid at sufficient pressure to support a column of liquid within the tubing 5, which column extends a substantial distance above the unit I. Under these conditions the exterior of the bellows I8 is exposed to gas in the chamber II which is in communication through port I2 and passages I3 and I4 with the tubing 5, which is at relatively low pressure. At the same time the interior of the bellows I8 is exposed through the passages I9 and 20, the chamber 2| and the port 23, to the gas pressure within the casing which is considerably greater than the pressure within the tubing 5. This gas pressure expands the bellows I8 to force the push rod I'I down and open the valve I5, as shown in Fig. 1. At the same time the two bellows 3| and 32, respectively, are exposed to the relatively low gas pressure existing within the tube 5, which pressure acting upon the end wall 30 is insufiicient to overcome the force, exerted by spring 21 so that the latter holds the valve 26 against its seat. It should be noted at this point that by virtue of the-difference in area between the

end walls

29 and 30 of the two interconnecting bellows 3| and 32, respectively, the force on the push rod 28 resulting from fluid pressure within the passage I4 is always downward and is proportional to the fluid pressure existing in passage I 4.

Under the conditions outlined, the gas pressure in the casing, acting against the surface of the liquid in the casing, forces liquid from the casing up through the tubing I, past the check valve I0, through the passage 9 and the passage 35 into the chamber II, thence through port I2 and passages I3 and I4 into the tubing 5. As the liquid rises in the tubing 5, it creates a pressure head within the passages of unit I through which it flows, which pressure head is proportional to the height of the column of liquid in tubing 5. This pressure is applied to the exterior of the bellows 3I and 32 andthe exterior of bellows I8. In the case of bellows I8, the pressure is opposed by the gas pressure existent in the casing and in the case of the bellows 3| and 32 by the gas pressure in the casing acting upon the under side of valve 26, and by the spring 21. At first the ratio of the fluid pressure in passage I4 to the fluid pressure in the casing is a very small fraction, but as the column of liquid rises in the tubing 5 and the pressure in passage I4 approaches the gas pressure in the casing, the aforementioned ratio increases and approaches unity. However, when this ratio reaches a predetermined value less than unity (which predetermined ratio is substantially equal to the ratio of the area of valve passage 24 to the sum of the valve passage area plus the difierence between 'of the bellows I 8, compressing the latter and lifting the push rod I! to permit the spring I6 to close the valve I5.. Since the pressure head of the column of liquid in tubing 5 is less than the pressure existing in the casing, gas continues to flow rapidly into the tubingv 5 past the valve 26, carrying the column of liquid in the tubing 5 above the unit up through the tubing to the surface and discharging it through the pipe 5.

Since the fluid pressure within the passages II and I4 is a function of the height of the column of liquid within the tubing regardless of the vertical position of that column, pressure is maintained on the exterior of the bellows I6 and on the bellows 3| and 32, holding the valve I5 closed and the valve 26 open until the column of liquid .is discharged from the tubing 5.. Immediately following the discharge of the column of liquid through the pipe 6, however, the gas back of the column of liquid which lifted it escapes rapidly through the ,pipe 6, permitting the gas pressure in the passages II and. I I to drop, whereupon the bellows 32 expands and bellows 3| contracts to lift push rod 28 and permit the spring 21 to close valve 26. The closing of valve 26 stops the flow of gas through the passage 20, thereby immediately increasing the pressure in chamber 2| and within the bellows I8, which expands the latter to force the push rod II down and open the valve I5. This completes a cycle of operation and a new cycle begins, the operation continuing indefinitely.

It is essential, in order that the valve I5 remain closed until a column of liquid being raised is discharged from the tubing 5, that the pressure in the passage I I remain as great as the pressure within the bellows I8. The pressure within the passage II is substantially the same as that within the tubing 5. However, the pressure within the casing and within passage 2I may be appreciably greater than the pressure within the tubing 5 during the lifting operation because of the pressure drop between passage 23 and passage I4 resulting fro friction. It is for this reason that the interior of the bellows I8 is connected by the nozzle I9 with a point in the constricted passage 20. Thus, because of the fact that the space in passage 26 surrounding the nozzle I9 is restricted, the gas rushes through this passage at very high velocity and, as a result of the well-known Venturi effect, has a reduced pressure because of its velocity. It is this reduced pressure which is applied through nozzle I9 to the interior of bellows I8, thereby insuring that the valve I5 will remain closed until the column of liquid being lifted in the tubing 5 is discharged through the pipe 6 and valve 26 closes.

The areaof the bellows I8 is preferably made large as compared to the effective area of the valve I5 so that the well pressure acting through the liquid in the passage 9 has little effect in determining the operation of valve I5. In other passage II and the passage 20, respectively.

On the other hand, it is preferred that the fluid pressure acting upon the opposite sides of the va1ve-26 play an important part in the opening and closing of that valve. Thus, it is desired that the valve 26 open and close in response to the creation of a predetermined ratio between the pressure existing 'in passage I4 (which is in communication with the tubing 5) and in passage 22 (which is in communication with the gas pressure in the casing) instead of being responsive to the absolute pressure in the passage I4. To this end, the difference between the areas of the bellows end

walls

29 and 30, respectively, is preferably made of the same order of magnitude as the effective pressure area of the valve 26. Under these conditions, the gas preseu-re-in the casing acting upon the inner side of the valve 26 maintains that valve in closed posi tion until the ratio of the pressure resulting from the head of liquid growing in the tubing 5 to the gas pressure in the casing reaches a predetermined value. As a result, if the gas pressure within the casing is maintained at relatively low v value, the valve 26 will open and the valve I5 will close when a relatively short column of liquid is accumulated in the tubing 5v and the low gas pressure will sufiice to lift this short column of liquid up out of the well. On the other hand, if a higher gas pressure is maintained in the casing, then the column of liquid within thev tubing 5 will grow to a greater height before the valve 26 opens and the valve I5 closes to lift the column of liquid out of the well. It will be apparent therefore that the pumping unit is self-compensating for variations in the operating gas pressure available in the casing.

It is to be understood, however, that the unit may be adapted for pumping columns of liquid of fixed height, independent of the gas pressure in the casing, by making the differential of the areas of the bellows ends 29 and 30 large as compared to the pressure area of the valve 26. Obviously, by'making this differential area of the bellows sufficiently large as compared to the pressure area of the valve 26, the gas pressure in the casing acting upon the lower side of valve 26. can be made to have verylittle controlli efiect on the movement of the valve. Under these conditions, the stiffness of the spring 21 is increased to provide the chief force opposing the force applied by the bellows to the push rod 28. 'Byvarying the force exerted by the spring 21, the valve 26 can be made to open in response to the pressure head of a column of liquid of predetermined height in the tubing 5 thereabove',

substantially irrespective of the gas pressure existent in the casing. In the preferred arrangement, in which the pressure area of the valve 26 iscomparable in magnitude with the differential of the bellows ends 29 and 36, the spring 21 is made relatively weak so that it is not a factor in determining the opening and closing of the valve 21 but merely serves to support the weight of the valve so that the latter will follow the push rod 28 when the latter lifts.

The cycle of operations previously described will be repeated regularly as long as there is sufllcient liquid pressure in the tubing 1 immediately below the unit I to build up a fluid head above the unit sufficient to trip the valves I5 and 26.

- The pressure of the liquid in the tubing I adjacent the unit depends upon the gas pressure within the casing and the liquid level of the easing. Obviously, if the liquid level drops too far below the unit I, then so much of the liquid head equivalent to the gas pressure within the casing will be employed in lifting the liquid within the tubing 1 up to the unit I that there will be insuflicient head within the tubing 5 to actuate the valves. However, until this point is reached, as the liquid supply diminishes and the liquid flows more slowly through the unit I, the gas valve 26 remains closed for longer periods of time until the fluid level builds up to a height in the tubing 5 suflicient to trip the valves. Thus there is no loss of gas and no decrease in efficiency as there is in other methods of gas-lift in which gas continues to discharge through the tubingregardless of a decrease in the amount of liquid available.

As an example of the approximate magnitude ofthe columns of oil that may be lifted with 11 pump as described, if it is assumed that the effective area of the gas valve 26 subjected to the gas pressure in the casing is of the sum of the differential area of the bellows 3| and 32 and the area of the valve 26 subjected to liquid pressure, then with a gas pressure of pounds per square inch, a liquid pressure in excess of 80 pounds per square inch would be required to open the valve 26. By converting the pounds per square inch unit pressure into feet of head, it will be seen that an operating gas pressure of 100 pounds per square inch will lift a liquid column of approximately 200 feet in height. This allows 20% of the total gas pressure for overcoming friction of the column of liquid as it moves up the tubing. In the same manner it may be determined that a gas pressure of 200 pounds per square inch will lift a 400 foot column of liquid to the surface on each cycle.

Although in most installations it will be found advisable to employ the valve I5 for preventing flow of fluids between the tubing I and the passage I4" while the valve26 is open, this valve I5 and its actuating bellows I8 may be dispensed with under certain conditions of pressure within the tubing I relative to the gas pressure in the casing. Thus if the pressure of the liquid within the tubing I is relatively low as compared to the gas pressure within the casing, then when the gas valve 26 opens the increase in the pressure within the passage I4, as a result of the free passage of gas from the casing past the valve 26,

.may be sufficient to prevent further flow of liquid up past the check valve I0 and actually tend to reverse the flow of liquid past the check valve ID, causing the latter to seat. This latter condition would usually result in an installation in which the normal liquid level in the well was below the unit I and the pressure within the tubing'I adjacent the unit is produced solely by thegaspressure within the casing acting upon the surface of the liquid in the casing surrounding the tubing I. However, in many instances the liquid pressure within the tubing I may be even greater than the gas pressure within the casing, under which condition, if the valve I5 were not provided, liquid would continue to flow into the passage I4 while gas was being discharged therethrough past valve 26, causing emulsification if oil containing water is being produced and also producing in the space below the rising column of oil in the tubing 5 a mixture of gas and liquid which greatly reduces the effective pressure acting upon the lower end of the main body of liquid being raised. A particular instance in which the liquid pressurewithin the tubing I may be greater'than the gas pressure employed to actuate the unit will be discussed later with reference to Fig. 5.

As may be gathered from previous description, it is desirable in an installation of the type disclosed in Fig. 1 that the unit I be positioned closely adjacent the liquid level in the casing in order that an excessive amount of the total gas pressure available will not be absorbed in liftconditions, if the single unit I, as shown in Fig. 1, were initially installed at such a point in the tubing as to bring the port 23 only a slight distance above the liquid level in the casing, then after the pump had been in operation for a period the liquid level might drop so far below the port 23 as 'to render the pump inoperative.

To avoid the foregoing difficulty, two or more pumping units may be installed in tandem in the tubing, the upper unit being above the initial level of the liquid in the casing and the lowest unit being adjacent but above the lowest level the liquid in the casing may drop to. Such an installation employing two units I and 2, respectively, is shown in Fig. 3. The upper unit 2 need not have a liquid inlet valve but only a gas inlet valve and its construction may be as shown schematically in Fig. 2, in which elements corresponding to those in Fig. I bear the same reference numerals with the sufix a. No separate detailed description of Fig. 2 is necessary.

In Fig. 3, assume that the level A is the initial level of liquid in the casing and that the upper unit 2 is positioned thereabove. Under these conditions the gas pressure in the casing acting against the liquid surface forces liquid up through the tubing I, through unit I, through that portion of the tubing 4 between units I and 2, and through unit 2 into the tubing 5 thereabove, until the pressure head at unit 2 approaches by a predetermined amount the gas pressure within the casing, whereupon the gas valve 260 (Fig. 2) opens to admit 'gas through port 24a and carry the column of liquid in tubing 5 above the unit out of the well.

Unit 2 continues to operate and unit I remains inactive until the liquid in the casing drops to level B which is below the port 24 in unit I. It is to be understood, of course, that the spacing between units I and 2 is less than the difference between the head of liquid produced in tubing 5 by the casing pressure, and the head required in tubing 5 at unit 2 to trip the gas valve in that unit.

When the liquid in the casing reaches the level B, or some other level below port 24 of unit I, the latter operates as previously described with reference to Fig. 1 and periodically lifts a column of liquid up through the tubing 5 through unit 2, which may or may not function depending upon whether its gas valve is set to open in response to a smaller or a larger head of liquid than is the gas valve of unit I.

If desired, a simple needle valve as shown in Fig. 10 may besubstituted for the unit 2 in Fig. 3 to admit a stream of gas from the casing into the tubing 5 to pump liquid by the ordinary gas-lift process until the level of liquid is brought downbelow unit I. The needle valve unit shown in Fig. 10 simply comprises a body member 40 adapted to be inserted between two sections of the tubing 5 and defining a passage 4| interconnecting the two tubing sections and a passage 42 communicating with the exterior. Passage 42 also communicates with the tubing 5 through a passage 43 having a valve seat on the upper edge thereof against which a needle valve 44 is forced by a spring 45. When the valve is opened, fluid can pass freely from passage 42 through passage 43, thence up around the needle valve 44 and into the tubing through passages 46. The spring 45 is retained in position by a threaded plug 41. The needle valve is normally maintained in closed position by the spring 45 and the latter is of such tension as to permit the needle valve to open only in response to a casing gas pressure substantially greater than that employed to operate unit I (Fig. 3) so that after the casing liquid level drops below unit I and the latter becomes operative, the casing gas pressurecan be reduced to a value too low to open the needle valve.

The advantages of using staged pumping units instead of one pumping unit and a needle valve are: (1) less gas pressure in the casing is required; (2) much less volume of gas is required; (3) there is much less danger of producing an emulsion when a mixture of oil and water is being pumped.

Under some circumstances it may be desirable to employ a packer about the tubing 1 below the unit I to prevent the casing gas pressure from being applied to the producing formation in the well. Such an arrangement is shown in Fig. 4, the packer being shown at 48. Except for the use of this packer 48, the installation in Fig. 4 is exactly the same as that in Fig. 1 which has been described in detail. The arrangement shown in Fig. 4 is particularly desirable in a well which produces a large volume of liquid at little or no pressure. The packer 48 is preferably positioned relatively close to the unit I and of course both must be positioned a substantial distance below the normal level of the liquid in the casing so that the liquid pressure below the packer 48 will be suflicient to force the liquid up through the unit I and into the tubing 5 and produce in the latter a column. of liquid to be lifted of substantial height. Gas pressure within the casing 4 above the packer 48 to lift the liquid must then be supplied from some external source through the pipe 8. In order to secure maximum production, the pressure of the gas supplied to the casing should be slightly in excess of the pressure head existing in the liquid below the packer 48.

In the arrangement of Fig. 4 there are two independent passages from the unit I to the surface; one through the tubing 5 and the other through the casing 4 surrounding the tube. Therefore, either one of these passages may be used for discharging the liquid and the other employed for supplying the gas pressure. In some instances it may be desirable to supply the gas under pressure through the tubing 5 and deliver the oil through the casing 4. This merely involves a re-design of the unit I, as shown schematically in Fig. 6, in which elements corresponding to those of Fig. l bear the same reference numerals with the suflix .b.

It will be observed that the unit comprises a standing valve l8b the same as in the unit of Fig. 1 and a liquid inlet valve I5b controlled by a spring I81) and a bellows l8b. However, the chamber III), in which the bellows l8b is mounted, communicates with the exterior through a port 58 instead of communicating with the tubing 5, as in Fig. 1. The bellows 3") and 32b are inverted and the exteriors of both are in communication with the exterior of the unit through

ports

50 and 5|. The valve 28b is likewise inverted and the passage 22 communicates with the tubing 5 through a Venturi passage 28b. The interior of the bellows III) is communicated through a passage 52 and a nozzle I9b with the Venturi passage 20b.

By comparing the construction of the unit shown in Fig. Ii with that shown in Fig. 1, it will be observed that gas pressure in the tubing 5 acts upon the bellows l8b to open the valve I51) and permit liquid to flow from the tubing 1 up past the check valve lb and the valve I51:

through the port 50, into the casing above the packer 48. A column of liquid will rise in the casing until its head is suflicient to actuate the bellows III!) and the bellows l8b to open the valve 28b and close the valve I5b, whereupon gas will be discharged from the tubing 5 down past the valve 26b and out through port 5I into .the casing to lift the column of liquid in the casing. One advantage of employing the arrangement shown in Fig. 6 instead of that shown in Fig. 4 is that the unit I and the packer 48 may be initially installed at any desired depth of oil in the casing 4 since gas can always be supplied to the unit through the tubing 5 regardless of the height of the liquid surrounding the tubing.

Still another system in which my unit may be employed is illustrated in Fig. 5, in which the unit I corresponding to the unit shown inFig. 1 is inserted in a string of tubing 55, which in turn is positioned within an outer tubing 58 mounted within the well casing 4. A seat 51 is provided in the tubing 56 which supports the unit I and seals with the latter. Tubing 58 may be extended below the seating member 51 to serve as a gas anchor. The tubing 59 below the unit I extends into the liquid to be pumped; The tubing 55 is open at the upper end for the discharge of liquid and gas but the tubing 56 and the casing 4 are sealed ofi at the top and gas from casing 4 is supplied through a reducing valve 68 to the tubing 56 to actuate the unit I.

The system of Fig. 5 is particularly adapted for oil wells in which the oil production is small and the gas pressure is large and it is necessary to apply a reduced gas pressure to the unit I in order to limit the pumping capacity to the producing capacity of the well. By choosing a pressure reducing valve '68 of the proper characteristics, any desired gas pressure may be -supplied to the tubing 56 to cause the unit I to pump at a Y low capacity.

It should be noted that in an installation of the type disclosed in Fig. 5 it is absolutely necessary that the unit I have a liquid inlet valve I5 (Fig. 1) since the pressure of the liquid supplied to the unit may be much greater than the gas pressure employed to lift the liquid. Therefore if, when valve 26 opened, the valve I5 did not close, large quantities of liquid would still enter the tubing above the unit and would be mixed with the gas, causing the entire system to operate as a conventional gas-lift system.

Obviously a unit of the type disclosed in Fig. 6 may be employed in-a system as shown in Fig. 5 and the gas pressure supplied to the tubing 55 and the oil exhausted through the tubing 56. It is also understood that gas to operate the unit may be supplied from a separate source instead *of from the casing 4.

Units of the type disclosed in the schematic diagrams of Figs. 1 and 2 may be constructed in actual practice as shown in Figs. 7, 8 and 9, respectively. Thus Fig. 7 showsthe upper portion and Fig. 8 shows the lower portion of an actual unit corresponding to the unit I in Fig. 1. It will be observed that this unit comprises an. upper tubular member 65 adapted to screw onto the lower end of the tubing 5 and threaded at its lower end into a coupling member 86 which couples it to a second tubularmember 81 positioned therebelow, the latter in turn being threaded into a coupling member 68 which con- ,nects it to a tubular member 69 which at its lower end is threaded onto an adapter which connects to the tubing 1 below the unit. A valve valve 25 which seats against seat 8|.

seat II is clamped between the

members

69 and 10 which cooperates with the standing valve ID. The latter is preferably urged toward its seat by a. retainer 12 which is urged downward by a spring 13 seating against a shoulder 14 in the member 69.

The ball valve [5 is also mounted within the member 69 and is urged upward against its seat 15 by the spring l6 which is compressed between the shoulder 14 and a retainer 16 positioned below the ball l5. The push rod H for opening the valve l5 has a guide 1-! thereon slidably positioned within a passage provided therefor in the member 68 and is joined by a threaded shaft 18 to the lower end member 19 of the bellows l8. The bellows I8 is attached at its upper end to a rigid tubular member 88 which is threaded at its upper end into the coupling member 86.

The nozzle [9 is a separate member which is threaded into the upper end of the tubular member and extends into a valve seat 8| which defines the passage 28. The valve seat 8| is clamped in position between the coupling member 68 and a tubular guide member 82 which slidingly supports a retainer 83 for the check The coupling member 66 has longitudinal passages 84 extending therethrough which correspond to the passage l3 in 1 and it also has lateral passages 85 therein extending to the exterior, which correspond to the gas inlet passage 23 in Fig. 1.

The tubular member 82 supports a tubular member 88 to which it is joined by screw threads and the tubular member 86 is connected also by screw threads to the bellows anchor member 81 which supports the bellows 3| and 32, respec tively. The end wall 30 of the bellows 32 is constituted by a conical member into which the upper end of the shaft 28 is threaded. Likewise the end wall 29 of the lower bellows 3| is relatively thick or elongated and screws onto the lower end of the shaft 28 and onto the upper end of a shaft 28' which constitutes the push rod for opening the ball valve 26. A guide 88 is mounted upon the rod 28, the ball 26 seats against a seat 89 clamped between the

members

82 and 86, respectivel and the ball is normally urged against its seat by the spring 21, through a retainer 90.

The various passages through the units shown in Figs. 7 and 8 may be traced from bottom to top as follows: The tubing 1 communicates through the hollow member I0 and the seat 'H' past the check valve I 0 with the passage 9 within the hollow member 69, thence past valve I5 when the latter is open, through the seat 15, past the guide 11 into the passage ll surrounding the bellows l8, from thence through the passages 84 into the space defined between the outer tubular member 85 and the

members

82 and 86, and the bellows supporting element 81, to the tubing 5. Gas entering through the ports 23 goes through the passages 85, through the valve seat 20, thence up past the guide 83, past the valve 28, through the seat 89, past the guide 88, at which point it communicates with the space between the tubular member 86 and the outer casing member 65 through ports 9|. I

The unit shown in Fig, 9 corresponds exactly with the upper portion of the unit I shown in Fig. '7 and corresponding parts bear the same reference numerals with the suffix: (2 added thereto. The only difference is that instead of the member 80, the member 61 and the parts positioned therebelow being employed, the tubing 5a connected to the lower ,end of the unit is joined directly through an adapter 92 to the lower end of the coupling member 86a.

Although the invention has been described with reference to several specific systems and by disclosing in detail one possible method of construction, it is to be understood that changes may be made in the system and in the particular constructions disclosed without departing from the invention and the latter is to be limited only as set forth in the appended claims.

I claim:

1. In a gas-lift pumping system for a well having a casing containing liquid to be pumped in the lower portion thereof and gas under pressure in the casing above the liquid surface therein; a string of tubing within the casing having its upper end extending out of the casing and its lower end submerged in the liquid in the casing, gas valve means for admitting gas from said casing into said tubing at a first level, liquid valve means for controlling flow of fluid through said tubing from a level below said first level, and means for closing said gas valve and opening said liquid valve when the pressure in the tubing falls below a predetermined value and for opening said gas valve and closing said liquid valve when the fluid pressure in the tubing at said first level reaches a predetermined ratio with respect to the gas pressure in said casing, whereby a column of liquid rises in said tubing when said liquid valve is open until the pressure head of said column reaches said predetermined ratio with respect to the gas pressure in said casing and said column of liquid is then lifted up through said tubing by gas admitted therebelow through said gas valve.

2. In a gas-lift pumping system for a well having a casing containing liquid to be pumped in the lower portion thereof, the surface of said liquid varying between a lower level and an upper level and gas under pressure in the casing above the liquid surface therein, the gas pressure being suflicient to support a column of said liquid of a height less than thedepth of said well to said liquid surface; an open ended string of tubing within the casing having its upper end extending out of the casing and its lower end submerged in said liquid at a point below said lower level, first valve means for communicating said tubing with the casing at a first level above said upper level in response to increase of fluid pressure Within said tubing at said first level above a predetermined valueless than the gas pressure in the casing, second valve means for communicating said tubing with the casing at a second level below said first level but above said lower level of liquid in the casing, in response to increase of fluid pressure within said tubing at said second level above a predetermined value less. than the fluid pressure in the casing at said second level, said first valve means closing at tubing pressures at said first levelbelow a predetermined value less than said first mentioned predetermined value, and said second valve means closing at tubing pressures at said second level below a predeterimned value less than said second mentioned predetermined value, and the distance between said first and second valves being less than the height of a liquid column having a pressure head equal to the difference between the gas pressure in the casing and said first-mentioned predetermined pressure.

3. In a gas-lift pumping system for a well having a casing containing liquid to be pumped in the lower portion thereof, the surface of said liquid varying between a lower level and an upper level, and gas under pressure in the casing above the liquid surface therein, a string of tubing within the casing having its-upper end extending out of the casing and its lower end submerged in said liquid at a point below said lower level, first valve means for communicating said tubing with the casing at a first level adjacent said upper level in response to an increase of the ratio of the fluid pressure within said tubing at said first level to the fluid pressure in the casing at said first level to a predetermined value less than unity, second valve means for communicating said tubing with the casing at a second level below said first level but adjacent said lower level of liquid in the casing in response to an increase of the ratio of the fluid pressure within said tubing at said second level to the fluid pressure in the casing at said second level to a predetermined value less than unity, said first valve means closing in response to a decrease in the tubing pressure at said first level below a predetermined value and said .second valve means closing in response to a decrease in the tubing pressure at said second level below a predetermined value.

4. In a gas-lift pumping system for a well having a casing containing liquid to be pumped in the lower portion thereof, the surface of said liquid vary ng between a lower level and an upper level, and gas under pressure in the casing above the liquid surface therein; an' open ended string of tubing within the casing having its upper end extending out of the casing and its lower end submerged in said liquid at a point below said lower level, first valve means for communicating said tubing with the casing at a first level above said upper level in response to increase offluid pressure within said tubing at said first level above a predetermined value less than the gas pressure in the casing, second valve means for communicating said tubing with the casing at a second level below said first level but above said lower level of liquid in the casing in response to increase of fluid pressure within said tubing at said second level above a predetermined value less than the fluid pressure in the casing at said second level, said first valve means closing at tubing pressures at said first level below a predetermined value less than said first mentioned predetermined value and said second valve means closing at tubin pressures at said'second level below a predetermined value less than said second mentioned predetermined value, the distance between said first and second valves being less than the height of a liquid column having a pressure head equal to the diflerence between the gaapressure in the casing and said first-mentioned predetermined pressure, and third valve means for closing said tubing at a level adjacent and below said second level in response to increase of fluid pressure within said tubing at said second level to a'value above said second mentioned predetermined value.

5. A gas-lift pumping system for a well having a casing containing liquid to be pumped in the lower portion thereof, the surface of said liquid varying between a lower level and an upper level, and gas under pressure in the casing above the liquid surface therein, a string of tubing within the casing having its upper end extending out of the casing and its lower end submerged in said liquid at a point below said lower level, first valve means for communicating said tubing with the casing at a first level adjacent the said upper level in response to an increase in the ratio of the fluid pressure within said tubing at said first level to the fluid pressure in the casing at said first level above a predetermined value less than unity, second valve means for communicating said tubing with the casing at a second level below said I, first level and adjacent said lower level of liquid in the casing in response to an increase in the ratio of the fluid pressure within said tubing at the second level to the fluid pressure in the casing at said second level above a predetermined value less than unity, said first valve means closing in response to reduction of tubing pressure at said first level below a first predetermined value, and said second valve means closing in revalue.

6. In a gas-lift pumping system for a well having a casing containing liquid to be pumped in the lower portion thereof and gas at relatively high pressure thereabove; a first string of tubing within the casing and extending into the liquid therein, and a second string of tubing within said first tubing, the first tubing being closed at the top and the second tubing open at the top, means sealing said first tubing. about said second tubing adjacent the liquid within said well, means for admitting gas at reduced pressure from said casing into said first tubing at a point above said sealing means, a first valve means for admitting gas from said first tubing into said second tubing adjacent and above said sealing means, second valve means for controlling the flow of fluid through said second tubing at a point below the point of admission of gas thereinto, and means for opening said first valve means and closing said second valve means in response to fluid pressure within said second tubing of predetermined magnitude relative to and less than the fluid pressure within said first tubing and closing said first valve means and opening said second valve means in response to decrease in the fluid pressure within said second tubing below a predetermined value less than said first predetermined value whereby a column of liquid rises in said second tubing through said second valve until the pressure head of said column reaches said first predetermined value, whereupon said column of liquid is lifted up through said tubing by gas admitted therebelow from said first tubing through said first valve.

7. In a gas-lift pumping system for a well having a casing containing liquid to be pumped in the lower portion thereof and gas at relatively high pressure thereabove; a first string of tubing within the casing and extending into the liquid therein and a second string of tubing within said first tubing, means sealing said first tubing about said second tubing adjacent the liquid level within said well, means for admitting gas at reduced pressure from said easing into said first tubing at a point above said sealing means, a gas valve means for admitting gas from said first tubing into said second tubing adjacent and above said sealing means, liquid valve means for controlling flow of liquid from said casing below said gas valve means through said second tubing, and means responsive to the pressure in said second and first tubings, respectively, for opening said gas valve and closing said liquid, valve when the ratio of'the pressure in the second tubing to the pressure in the first tubing exceeds a predetermined value less than unity and for closing said gas valve means and opening said liquid whereupon said column of liquid is lifted up.

through said second tubing by gas admitted therebelow from said first tubing through said gas valve.

8. In a gas-lift pumping system for a well having a casing containing liquid to be pumped in the lower portion thereof, a string of tubing within the casing having its lower end submerged in the liquid therein, means for supplying gas under pressure to said tubing at the surface, valve means for supplying gas from said tubing into the casing at a point below the normal liquid level therein, said valve seeking its closed position in the absence of fiuid pressure in said tubing and casing, and means responsive to fluid pressure existing in said casing for opening said valve means when the pressure in the casing rises to a predetermined value less than the gas pressure in said tubing and closing said valve means when the pressure in the casing falls below a value less than said predetermined value, said valve remaining open in response to all casing pressures exceeding said predetermined value.

9. In a gas-lift pumping system for a well having a casing containing liquid to be pumped in the lower portion thereof, a string of tubing within the casing having its lower end submerged in the liquid therein, means for supplying gas under pressure to said tubing at the surface, valve means for admitting gas from said tubing into the casing at a point below the normal liquid level therein, and means responsive to fiuid pressures existent in the casing and in said tubing, respectively, for opening said valve means when the ratio of the pressure in the casing to the pressure in the tubing reaches a predetermined value less than unity and closing said valve means when the pressure in the casing falls below a predetermined value.

10. In a gas-lift pumping system for a well having a casing containing liquid to be pumped in the lower portion thereof, a string of tubing within said casing having its upper end extend- I ing out of said casing, and its lower end submerged in said liquid, means sealing, between said tubing and the casing at a point adjacent the normal liquid level therein, means for supplying gas under pressure to said tubing at the surface, gas valve means for discharging gas from said tubing into said casing at a point adjacent to and above said sealing means, liquid valve means for controlling flow of liquid from the casing below the sealing means to thecasing above the sealing means, and means for opening said gas valve means and closing said liquid valve means in response to fluid pressure in said casing at a level adjacent said sealing means greater than a predetermined pressure, which predetermined pressure is less than the gas pressure in said tubing, and closing said gas valve and opening said liquidvalve in response to de-,

crease of the pressure in said casing below a predetermined value less than said first mentioned predetermined value whereby a column of liquid rises in the casing above said sealing means through said liquid valve until the pressure head of said column reaches said first predetermined value whereupon said column of liquid is lifted up through the casing by gas admitted therebelow from said tubing through said first valve.

11. In a gas-lift pumping system for a well having a casing containing liquid to be pumped in the lower portion thereof, a string of tubing within said casing having its upper end extending out of said casing and its lower end submerged in said liquid, means sealing between said tubing and the casing at a point adjacent the normal liquid level therein, means for supplying gas under pressure to said tubing at the surface,

gas valve means for discharging gas from said tubing into said casing at a point adjacent to and above said sealing means, liquid valve means for controlling flow offluid from the casing below the sealing means to the casing above the sealing means, means for opening said liquid valve means and closing said gas valve means in response to a decrease in the pressure in said casing below a predetermined value, and means for opening said gas valve means and closing said liquid valve means in response to increase 01' the ratio of the fluid pressure in said casing above said sealing means to the gas pressure in said tubing above a predetermined value less than unity, whereby a column of liquid rises in the casing above said sealing means through said liquid valve until said predetermined ratio is exceeded whereupon said column of liquid is lifted up through the casing from gas admitted therebee low from said tubing through said gas valve.

12. A gas-lift pumping unit adapted for insertion in a well and defining a first passage for the entry of well fluid, a second passage for the discharge of well fluid to the surface, and a third passage for supplying gas-under pressure to said second passage, gas valve means interconnecting said second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through said second passage, liquid valve means interconnecting said first and second passages for passing well fluid from said first passage to said second passage, first means for intermittently opening said gas valve to admit gas from said third passage to said second passage to elevate a column of liquid in said second passage up therethrough and out of the well, and closing said gas valve to permit a new column of liquid to form in said second passage, and second means mechanically independent of said first means for opening said liquid valve in response to closure of said gas valve and closing said-liquid valve in response to opening of said gas valve.

13. A gas-lift pumping unit adapted for insertion in a well and defining a first passage for the entry of well fluid, a second passage for the discharge of well fluid to the surface, and a third passage for supplying gas under pressure to said second passage, gas valve means interconnecting said second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through said second passage, liquid valve means interconnecting said first and second passages for passing well fluid from said first passage to said second passage, means responsive to fluid pressure existt in said second passage for opening said gas valve when the pressure in the second passage exceeds a predetermined value and closing said gas valve when the pressure in the second passage falls below a predetermined value less than said first predetermined value, and second means for opening said liquid valve in response to closure of said gas valve and closing said liquid valve in response to opening of said gas valve.

14. A gas-liftpumping unit as described in claim 13 in which said gas valve comprises means defining a port between said third and second passages and a closure member movable toward a said port in the direction of fluid flow from said third to said second passage whereby frictional resistance of said closure member to said fluid flow tends to close said valve.

15. A gas-lift pumping unit adapted for insertion in a well and defining a first passage for the entry of well fluid, a second passage for the discharge of well fluid to the surface, and a third passage for supplying gas under pressure to said second passage, gas valve means interconnecting said second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through said second passage, liquid valve means interconnecting said first and second passages for passing said fluid from said first passage to said second passage, first means responsive to fluid pressure existent in said second and third passages, respectively, for opening said gas valve when the ratio of the pressurein the second passage to the pressure in the third passage exceeds a predetermined value less than unity and closing said gas valve when-the pressure in the second passage falls below a predetermined value, and second means for opening said liquid valve in response to closure of said gas valve and closing said liquid valve in response to opening of said gas valve. I 16'. A gas-1ift pumping unit adapted for insertion in a well and defining a first passage for the entry of well fluid, a second passage for the discharge of well fluid to the surface, and a third passage for supplying gas under pressure to said second passage, gas valve means interconnecting said'second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through said second passage, liquid valve means interconnecting said first and-second passages for passing well fluid from said first passage to said second passage, first meansresponsive to fluid pressures existent in said second and third passages, respectively, for opening said gas valve when the ratio of the pressure in the second passage to the pressure in the third passage exceeds a predetermined value less than unity and closing said first valve when the pressure in the second passage falls below a predetermined value, said gas valve comprising means defining a port between said third and second pas;- sages and a closure member movable toward said port in the direction of fluid flow therethrough' from said third to said second passage whereby frictional resistance of said closure member to said fluid flow tends to close said gas valve, and second means for opening said liquid valve in response to closure of said gas valve and closing said liquid valve in response to opening of said gas valve. 3

17. A gas-lift pumping unit adapted for insertion in a well and defining a first passage for the entry of well fluid, a second passage forthe discharge, of well fluid to the surface, and athird passage for supplying gas under pressure to said second passage. gas valve means interconnecting said second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through said second passage. liquid valve means interconnecting said first and second passages for passing well fiuid from said first passage to said second passage, first means responsive to fluid pressures existent in said second and third passages, respectively, for opening said gas valve when the ratio of the pressure in the second passage to the pressure in the third passage exceeds a predetermined value less than unity and closing said gas valve when the'pressure'in the second passage falls below a predetermined value,

said first pressure responsive means including means responsive at all times to pressure in said secondpassage for tending to open the gas valve in response to such pressure, and means responsive to pressure in said third passage only when said gas valve is closed tending to close said gas valve in response to third passage pressure whereby closing force on said gas valve increases as the valve moves from open to closed position, and second means for opening said liquid valve in response to closure of said gas valve and closing said liquid valve in response to opening of said gas valve.

18. A gas-lift pumping unit adapted for insertion in a well and defining a first passage for the entry of well fluid, a second passage for the discharge of well fluid to the surface, and athird passage for supplying gas under pressure to said second passage, gas valve means interconnecting said second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through said second passage, liquid valve means interconnecting said first and second passages for passing well fluid from said first passage to said second passage, first means for intermittently opening said gas valve to admit gas from said third passage to said second passage to elevate a column of liquid in said second passage up therethrough and out of the well and closing the gas valve to permit a new column of liquid to form in said second passage, and second means for opening said liquid valve in response to closure of said gas valve and closing said liquid valve in response to opening of said gas valve, in which said gas valve and means for opening and closing it comprise a port between said third and second passages, a closure member movable toward and away from said port on the third passage side thereof, auxiliary means responsive to pressure in said second passage for urging said closure member into open position, and yieldable means for urging said closure member into closed position.

19. A gas-lift pumping unit adapted for insertion in a well and defining a first passage for the entry of well fluid, a second passage for the discharge of well fluid to the surface, and a third passage for supplying gas under pressure to said second passage, gas valve means interconnecting said second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through said second passage, liquid valve means interconnecting said first and second passages for passing well fluid from said first passage to said second passage, flrst means for intermittently opening said valve to admit gas from said third passage to said second passage to said gas valve to permit a new column of liquid to form in said second passage, second means for opening said liquid valve in response to closure of said gas valve and closing said liquid valve in response to, opening of said gas valve, in which said gas valve and means for opening and closing it comprise a valveseat defining a port interconnecting said thir and second passages, a valve movable toward and away from said seat whereby said valve when seated exposes eifective pressure areas to fluids in said third and second passages, respectively, the pressure in said third passage tending to urge said valve against its seat, and additional means comprising a pair of members each having an outer face responsiveto fluid pressure in said second passage for applying an opening force to said valve which is proportional to the fluid pressure in the second passage, one of said members exposing a face of a larger efiective pressure area than the other and tending to move in such direction as to open said valve.

20. A gas-lift pumping unit adapted for insertion in a well and defining a first passage for the entry of Well fluid, a second passage for the discharge of well fluid to the surface, and a third passage for supplying gas under pressure to said second passage, gas valve means interconnecting said second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through said second passage, liquid valve means interconnecting said first and second passages for passing well fluid from said first passage to said second passage, first means for intermittently opening said gas valve to admit gas from said third passage to said second passage to elevate a column of liquid in said second passage up therethrough and out of the well, and closing said gas valve to permit a new column of liquid to form in said second passage, second means for opening said liquid valve in response to closure of said gas valve and closing said liquid valve in response to opening of said gas valve, said gas valve and means .for opening and closing it comprising a valve seat defining a port interconnecting said third and second passages, a closure member movable toward and away from said seat whereby said closure member when seated exposes effective pressure areas to fluids in said second and third passages, respectively, pressure in said third passage tending to urge said valve against its seat, and additional means comprising a pair of members each having an outer face responsive to fluid pressure in said second passage for applying an opening force to said valve which is proportional to the fluid pressure in the second passage, one of said members exposing a face of larger effective pressure area than the other and tending to move in such direction as to open said closure member, and means further provided for yieldably resisting the opening force of the said member applied to said valve.

21. A gas-lift pumping unit adapted for insertion in a well and defining a first passage for the entry of well fluid, a second passage for the discharge of well fluid to the surface, and a third passage for supplying gas under pressure to said second passage, gas valve means interconnecting said second and thirdpassages for admitting gas under pressure to discharge a column of liquid upwardly through said second passage, liquid valve means interconnecting said first and second passages for passing well fluid from said first passage to said second passage, first means for intermittently opening said gas valve to admit gas from said third passage 'to said second passage to elevate a column of liquid in said second passage up therethrough and out oi the well, and closing said gas valve to permit a new column of liquid to form in said second passage, second means for opening said liquid valve in response to closure of said gas valve and closing said liquid valve in response to opening of said gas valve, said gas valve and means for opening and closing it comprising a valve seat defining a port interconnecting said third and second passages, a closure'member movable toward and away from said seat, spring means for applying a force tending to-close said closure member, and means comprising a pair of members each having an outer face responsive to fluid pressure in said second passage for applying an opening force to said valve which is proportional to the fluid pressure in the second passage, one of said members exposing a face having a larger efiective pressure area than the other and tending to move in response to pressure in such direction as to open said valve, a fluid-tight means supporting said pair of members and defining with said members a closed chamber, means coupling the faces of the said members together for simultaneous movement, and means operable by said pair of members for opening said closure member in response to inward movement of said member of larger face area.

'22. A gas-lift pumping unit adapted for insertion in a well and defining a first passage for the entry of well fluid, a second passage for the discharge of well fluid to the surface, and a third passage for supplying gas under pressure to said second passage, gas valve means interconnecting said second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through said second passage, liquid valve, means interconnecting said first and second passages for passing well fluid from said first passage to said second passage, first means for intermittently opening said gas valve to admit gas from said third passage to said second passage to elevate a column of liquid in said second passage up therethrough and out of the well, and closing said gas valve to permit a new column of liquid to form in said second passage, said liquid valve means comprising a check valve mechanically independent of said first means for permitting fluid flow from said first to said second passage and preventing fluid flow from said second to said first passage.

23. A gas-lift pumping unit-adapted for insertion in a Well and defining a first passage for the entry of well fluid, a second passage for the discharge of well fluid to the surface, and a third passage for supplying gas under pressure to said second passage, gas valve means interconnecting said second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through" said second passage, liquid valve means interconnecting said first and second passages for passing well fluid from said first passage to said second passage, first means for intermittently opening said gas valve to admit gas from said third passage to said second passage to elevate a column of liquid in said second passage up therethrough and out of the well, and closing said gas valve to permit a new column of liquid to form in said second passage, and second means mechanically independent of said first means responsive to fluid pressure in said second and third passages, respectively, for opening said liquid valve when the pressure in thethird passage exceeds the pressure in the second passage by a predetermined difierential andv closing the liquid valve in response to a decrease in the said differential pressure below a predetermined value.

24. A gas-lift pumping unit adapted for insertion in a well anddefining a first passage for the entry of well fluid, a second passage for the discharge of well fluid to the surface, and a third passage for supplying gas under pressure to said second passage, gas valve means interconnecting said second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through said second passage, liquid valve means interconnecting said first and second passages forl passing well fluid from said first passage to said second passage, first means for intermittently opening said gas valve to admit gas from said third passage to said second passage to elevate a column of liquid in said second passage up therethrough and out of the well, and closing said gasvalve to permit a new column of liquid to form in said second passage, and second means responsive to fluid pressures in said second and third passages, respectively, for opening said liquid valve when the pressure in the third passage exceeds the pressure in the second passage and closing said liquid valve in response to increase of the pressure in the second passage to a value substantially equal to the pressure in the third passage.

25. A gas-lift pumping unit adapted for insertion in a well and defining a first passage for the entry of well fluid, a second passage for the discharge of well fluid to the surface, and a third passage for supplying gas under pressure to said' 30 second passage, gas valve means interconnecting said second and third passages for admitting I gas under pressure to discharge a column of liquid upwardly through said second passage, liquid valve means interconnecting said first and second passages for passing well fluid from said first passage to said second passage, first means for intermittently opening said gas valve to admit gas from said third passage to said second passage to elevate a column of liquid. in said second passage up therethrough and out of the well, and closing said gas valve to permit a new column 'of liquid to form in said second passage, and second means for actuating said liquid valve comprising a member having a pressure face exposed to pressure in said third passage and tending to open the liquid valve and a pressure face exposed to pressure in said second passage and tending to close said liquid valve whereby said valve opens and closes in response to variations in the differential pressure of said second and third passages.

26. A gas-lift pumping unit as described in claim 25, in which the pressure faces on said second means, are of substantially equal areas whereby said second means tends to open said liquid valve in response to increase of the pressure in the third passage above the pressure in the second passage.

2'7. A gas-lift pumping unit adapted for insertion in a well and defining a first passage for the entry of well fluid, a second passage for the discharge of well fluid to the surface, and a third passage for supplying gas under pressure to said second passage, gas valve means interconnecting said second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through said second passage, liquid valve means interconnecting said first and second passages for passing well fluid from said first passage to said second-passage, first means for intermittently opening said gas valve to'admit gas from said third passage to said second passage to elevate a column of liquid in said second passage up therethrough and out of the well, and closing said gas valve to permit a new column of liquid to form in said second passage, and second means responsive to fluid pressure in said second and third passages, respectively, for opening said liquid valve when the pressure in the third passage exceeds the pressure in the second passage by a predetermined difierential, and additional means responsive to the opening of said-gas valve for varying the last mentioned pressure differential locally about the second pressure responsive means whereby the pressure in the second passage is effective to close the liquid valve'when said gas valve is open. r

28. A gas-lift pumping unit adapted for insertion in a well and defining a first passage for the entry of well fluid, a second passage for the discharge of well fluid to the surface, and a third passage for supplying gas under pressure to said second passage, gas valve means interconnecting said second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through said secondipassage, liquid valve means interconnecting said first and second passages for passing well fluid from said first passage to said second passage, first means for intermittently opening said gas valve to admit gas from said third passage to said second passage to elevate a column of liquid in said second passage up therethrough and out of the well, and closing said gas valve to permit a new column of liquid to form in said second passage, second valve control means responsive to fluid pressures existent in said second and third passages, re-

spectively, for opening said liquid valve when the pressure in the third passage at the point therein where it afiects said second valve control means exceeds the pressure in the second passage,

and closing said liquid valve when the pressure in the second passage is substantially equal'to the pressure at said point in the third passage, and means for locally reducing the pressure at said point in said third passage when said first valve is open.

29. A gas-lift pumping unit adapted for insertion in a well and defining a first passage for the entry of well fluid, a second passage for the discharge of well fluid to the surface, and a third passage for supplying gas under pressure to said second passage, gas valve means interconnecting said second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through said second passage, liquid valve means interconnecting said first and second passages for passing well fluid from said first passage to said second passage, first means for intermittently opening said gas valve to admit gas from said third passage to saidsecond passage to' elevate a column of liquid in said second passage up therethrough and out of the well, and closing said gas valve to permit a new column of liquid to form in said second passage, second I means responsive to fluid pressures existent in said third and second passages, respectively, for opening said liquid valve when the pressure in the third passage where it afiects said second valve control means exceeds the pressure in the second passage and closing said liquid valve when the pressure in the second passage exceeds the pressure at the point in the third passage where it affects said second valve control means, and pressure reducing means acting upon the fluid at said point in said third passage for reducing the pressure of the fluid locally at that point when said first valve is open. I l

130. A gas-lift pumping unit adapted for insertion in a well and defining a. first passage for the entry of well fluid, a second passage for the discharge of Well fluid to the surface, and a third passage for supplying gas under pressure to said second passage, gas valve means interconnecting said second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through said second passage, liquid valve means interconnecting said first and second passages for passing well fluid from said first passage to said second passage, first means for intermittently opening said gas valve to admit gas from said third passage to said second passage to elevate a column of liquid in said second passage up therethrough and out of the well, and closing said gas valve to permit a new column of liquid to form in said second passage, second means responsive to fluid pressures existent in said second and third passages, respectively, for opening said liquid valve when the pressure at a predetermined point in the third passage exceeds the pressure in the second passage, and closing said liquid valve when the pressure in the second passage is substantially equal to the pressure at said predetermined point in the third passage, and means including a Venturi constriction for reducing the fluid pressure at said predetermined point when fluid is admitted through the third passage and said gas valve, to reduce the pressure of that fluid locally where it is effective on the second valve control means to a value substantially equal to or below the pressure of the fluid in the second passage where it is efiective on said second control means.

31. A gas-lift unit comprising a body member adapted for insertion in a Well and defining a first passage for communication with liquid in the well, a second with a liquid discharge line extending out of the well and a third passage for communication with a source of gas under pressure, means interconnecting said first and second passages for admitting liquid from the well into said liquid discharge line; means including a valve interconnecting said second and third passages for admitting gas under pressure from said source to the liquid discharge line to lift a column of liquid therein up out of the well, and valve control means therefor; said valve and valve control means comprising a valve seat defining a port interconnecting said second and third passages, a valve movable toward and away from said seat whereby said valve when seated exposes equal.

eiTective areas to fluids in said second and third passages, respectively, the pressure in said third passage tending to urge said valve against its seat and the pressure in said second passage tending to open said valve, and additional means responsive to fluid pressure in said second passage for applying an opening force to said valve whichnsproportional to the fluid pressure in the second passage.

32. A gas-lift pumping unit comprising a body member adapted for insertion in a well and defining a first passage for communication with liquid in the well, a second passage for communication with a liquid discharge line extending out of the well and a third passage for communicating with a source of'gas under pressure; means interconnecting said first and second passages for admitting liquid from the well into said liquid discharge line; means including a valve interconnecting said second and third passages for admitting gas under pressure from said source to the liquid discharge line to lift a column of liquid therein up out of the well, and valve control means therefor; said valve and control means passage for communication comprising a valve seat defining a port interconnecting said second and third passages, a valve movable against and away from said seat, spring means for applying a force tending to close said valve, and means responsive to fluid pressure in said second passage for applying an opening force to said valve which is proportional to the fluid pressure in the second passage.

33. A gas-lift pumping unit comprising a body member adapted for insertion in a well and defining a first passage for communication with liquid in the well, a second passage for communication with a liquid discharge line extending out of the well and a third passage for communication with a source of gas under pressure; means interconnecting said first and second passages for admitting liquid from the well into said liquid discharge line; means including a valve interconnecting said second and third passages for admitting gas under pressure from said source to the liquid discharge line to lift a column of liquid therein up out of the well; valve control means responsive to fluid pressure existent in said second and third passages, respectively, for closing said valve when the pressure in the second passage decreases to a predetermined value and opening said valve when the pressure in the second passage reaches a predetermined ratio with respect to the pressure in the third passage; and a check valve in series with said valve for preventing movement of fluid from said second to said third passage while permitting movement of fluid from said third passage to said second passage.

34. A gas-lift pumping unit comprising a body member adapted for insertion in a Well and defining a first passage for communication with the liquid in the well, a second passage for communication with a liquid discharge line extending out of the well, and a third passage for communication with a source of gas under pressure; means interconnecting said first and second passages for admitting liquid from the well into said liquid discharge line; means including a valve interconnecting said second and third passages for admitting gas under pressure from said source to the liquid discharge line to lift a column of liquid therein up out of the well, and valve control means therefor; said valve and valve control means comprising a valve seat defining a port interconnecting said second and third passages, a valve movable toward and away from said seat whereby said valve when seated exposes equal effective pressure areas to fluids in said second and third passages, respectively, pressure in said third passage tending to urge said valve against its seat, and additional means comprising a pair of members each having an outer face responsiveto fluid pressure in said second passage for applying an opening force to said valve which is proportional to the fluid pressure in the second passage, one of said members exposing a face of a larger effective pressure area than the other, and fluid-tight means supporting said members and defining with said members a closed chamber, means coupling the faces of the said members together for simultaneous movement, and means operable by said members for opening said valve in response to pressure responsive movement of said member of larger face area.

35. A gas-lift pumping unit adapted for insertion in a well and defining a first passage for the entry of well fluid, a secondpassage for the discharge of well fluid to the surface, anda third passage for supplying gas under pressure to said i aromas second passage, gas valve means interconnecting said second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through said second passage, means interconnecting said first and second passages for passing fluid from said first passage to said second passage, and means responsive to fluid pressures existent in said second and third passages, respectively, for opening said gas valve when the pressure in the second passage reaches a predetermined ratio with respect to the pressure in the third passage, and closing said gas valve when the pressure in the second passage falls below a predetermined value.

36. A gas-lift pumping unit adapted for insertion in a well and defining a first passage for the entry or well fluid, a second passage for the discharge of well fluid to the surface and a third passage for supplying gas under pressure to said second passage, gas valve means interconnecting said second and third passages for admitting gas under pressure to discharge a column of liquid upwardly through said second passage, means interconnecting said first and second passages for passing fluid from said first passage to said sec ond passage, and means responsive to fluid pressures existent in the second and third passages, respectively, for opening said gas valve when the ratio of the pressure in the second passage to the pressure in the third passage exceeds a predetermined value less than unity and closing said gas valve when the pressure in the second passage falls below a predetermined value, and a check valve inserted in series with said gas valve between said second and third es for permitting fluid fiow from said third passage to said second passage and preventing fluid flow from said second passage to said third passage.

37. A gas-lift pumping unit adapted for insertion in a well and defining a first passage for the entry of well fluid, a second passage for the dis- "charge of well fiuid to the surface and a third passage up therethrough and out of the well and closing said gas valve to permit a new column of liquid to form in said second passage, and second means responsive to fluid pressures in said second and third passages, respectively, for opening said liquid valve when the pressure in the third passage exceeds the pressure in the second passage and closing said liquid valve in response to increase of the pressure in the second passage to a value substantially equal to the pressure in the third passage, said second means also including means responsive to pressure in said first passage only when said liquid valve is closed tending to close said liquid valve in response to first passage pressure whereby the closing force on the liquid valve decreases as the valve opens, thereby causing the valve to open quickly.

GRANVILLE S. KNOX.