US3741686A

US3741686A - Self resonant drive for deep well pump

Info

Publication number: US3741686A
Application number: US00143082A
Authority: US
Inventors: E Smith
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-05-13
Filing date: 1971-05-13
Publication date: 1973-06-26
Anticipated expiration: 1990-06-26

Abstract

Resonant column pumping devices drive a liquid column in coincidence with the resonant oscillations of the column both in frequency and phase for maximum operating efficiency. A piston at the top of the column is driven at a speed corresponding to the half wave frequency, or an odd harmonic thereof, of the liquid column by using the resonant column frequency to control the frequency of application of the driving force impulses transmitted to the liquid column. Means comprising inertial means are coupled to the piston and include actuating means, such as a slideable plunger, inertially responsive to the position of the piston for actuating a position adjustable switch means. The switch means in turn controls the time of the occurrence of the application of the motion to the piston at the resonant frequency of the liquid column, and at the proper phase with relationship to the motion of the liquid column.

Description

[ June 26, 1973 [57] ABSTRACT Resonant column pumping devices drive a liquid column in coincidence with the resonant oscillations of the column both in frequency and phase for maximum operating efficiency. A piston at the top of the column is driven at a speed corresponding to the half wave frequency, or an odd harmonic thereof, of the liquid column by using the resonant column frequency to control the frequency of application of the driving force impulses transmitted to the liquid column. Means comprising inertial means are coupled to the piston and include actuating means, such as a slideable plunger, inertially responsive to the position of the piston for actuating a position adjustable switch means. The switch means in turn controls the time of the occurrence of iinited States Patent [191 Smith 1 SELF RESONANT DRIVE FOR DEEP WELL PUMP [76] Inventor: Edward W..Smith, PO. Box 27,

Milton, N.l-l. 03851 [22] Filed: May 13, 1971 [21] Appl. No.: 143,082

521 US. Cl. 417/240 [51] Int. F04! 7/00 [58] Field of Search....... 417/240, 241

[56] References Cited UNITED STATES PATENTS PATENTEUJUH 26 I975 FIELD OF THE INVENTION The present invention relates in general to means for automatically driving longitudinally resonant liquid column pumps. More particularly, this invention relates to an improved means for automatically driving these pumps at the desired resonant frequency of the column by using the resonant column periodic motion to control the frequency of application of the driving force pulsations to the liquid column, and the phase of application relative thereto BACKGROUND OF THE INVENTION In resonant column pumping devices such as the arrangement shown in the inventors previous US. Pat. No. 2,751,848'it is important that the impulses provided to drive the liquid column coincide with the oscillation of the column both in frequency and phase if maximum operational efficiency is to be achieved. In the arrangement disclosed in the above referred to patent an eccentric is employed to provide sinusoidal impulses to the column by means of a connecting rod which is coupled to a piston at the top of the column. The connecting rod includes a hydraulic clutch whose initial slippage permits the motor to gradually build up to the desired speed of rotation before locking in to the resonant longitudinal vibration of the liquid column.

While this prior art arrangement is simple and effective in most cases it does have a disadvantage when high pumping rates are required which in turn demand considerable compression of the liquid column. High pumping rates are necessary for example, when pumping from deep wells. The result is that, unless the column is sufficiently wide, the connecting rod cannot be moved through the necessary angle without striking the interior of the casing, unless the connecting rod is made extremely long. This would in turn require a very cumbersome connecting rod arrangement. Furthermore, with this prior art arrangement the impulses applied by the piston to the upper end of the liquid column may not ideally be of the same frequency as the resonant frequency of the liquid column, nor of the proper phase.

OBJECTS OF THE INVENTION Accordingly, it is a primary object of the present invention to provide an improved means for automatically driving longitudinally resonant liquid column pumps at the resonant frequency of the column by employing the resonant column periodic motion to control the frequency of application of the driving force pulsations to the liquid column, and the phase of application relative thereto.

Another object of the present invention is to provide an improved means-as in the preceding object that is preferably embodied in a pump demanding high liquid pumping rates.

A further object of the present invention is to provide an improved means as in the preceding object that can be employed in a relatively deep well having a liquid column of limited cross-section.

Still another object of the present invention is to provide an improved means as in the preceding objects that provides for efficient operation, can be durably constructed, and that is not cumbersome.

SUMMARY OF THE INVENTION The fundamental components of a resonant column pump include a well casing that is usually in the form of a cylindrical steel pipe which defines a liquid well column, and a fluid displacement member, such as a driven piston arrangement, at the top of the liquid well column. The well casing includes a one-way valve at the bottom of the well casing permitting liquid to flow into the well casing, and an outlet in the wall casing above the top of the liquid well column. Means are connected to the displacement member for periodically applying motion to the member at the resonant frequency of the liquid well column.

The improvement in accordance with the present invention comprises inertia means coupled to the member and including actuating means, such as a plunger, enertially responsive to the position of the member for actuating a switch means. The switch means includes at least one mechanically actuable switch. This switch assumes one position when the member is near its uppermost position and assumes another position when the member is near its lowermost position, whereby the means for periodically applying motion to the member is causing application of the motion when the switch is in the one position and is suspending application of the motion when the switch is in the other position.

In a preferred embodiment of the invention motion is imparted to a piston by means of a rack having one end connected to the piston and the other end connected to the inertia means, and a pinion gear mounted on a shaft which may be selectively coupled and decoupled from a drive source such as a motor. Electromechanical clutch means are provided intermediate the shaft and the motor, which means are in a motion imparting condition (clutch plates together) when the switch is in the one position and in a motion suspending condition (clutch plates separated) when the switch is in the other position.

Another feature that may be embodied in the present invention is a second switch comprising the switching means. The second switch is so positioned in relationship to the actuating means, so that as the displacement member ascends the second switch changes to the motion imparting position before the first switch assumes its on position. This second switch may be adjustably positioned so that the commencement of the compressing motion, provided by the means for periodically applying motion, may occur just as the displacement member reaches its uppermost position, or a very short time thereafter. In this way the imparting of the driving force can be closely controlled to occur in phase with the resonant phase of the liquid well column.

BRIEF DESCRIPTION OF THE DRAWINGS Numerous other objects, features and advantages of the invention should now become apparent upon a reading of the following detailed description of a preferred embodiment in conjunction with the accompanying drawings in which:

FIG. 1A is a partially schematic diagram of a preferred embodiment of a resonant column pumping system in accordance with the present invention;

FIG. 1B is a side view of a part of the system of FIG. 1A; and

FIG. 2 is a cross-sectional view of the inertial unit of FIGS. 1A and 1B.

DETAILED DESCRIPTION Referring now to FIG. 1A there is shown a casing 1 which defines a typical liquid column 2, and has a ball check valve 3 disposed at the bottom of the casing and an outlet opening 4 at the top of the casing through which the pumped liquid is discharged. The casing l may be constructed of a cylindrical steel pipe. The ball valve 3 is a one way valve that permits liquid to enter casing 1 during contraction of the liquid column but prevents the escape of the liquid during the expansion of the liquid column. The principles of operation of the basic resonant liquid column pump including casing 1 and a piston 5 which is disposed at the top of the liquid column, are discussed in detail in U.S. Pat. No. 2,75l,848 which is hereby incorporated by reference.

When the displacement member or piston 5 is caused to be pulsed at the half-wave frequency of the liquid column, the liquid column contracts and expands longitudinally at a frequency which is determined by the length of the column for any given liquid. When the liquid column contracts it creates a vacuum at the bottom of the column and the liquid to be pumped is drawn into the space so created. On the return stroke, however, when the column is expanding, the ball check valve 3 prevents the liquid just drawn into the column from being forced back out again. As a result the entire column 2 lifts by an amount equal to the amount of liquid initially drawn in, and this liquid may be drawn off through the outlet opening 4 at the top of the casing 1.

Referring to FIGS. 1A and 1B, a rack 6 having a plurality of spaced teeth is secured by suitable means such as by welding to the top of piston 5. A pinion gear 7 engages with the teeth of rack 6 and is in turn mounted on one end of a shaft 8 which also carries a pair of slip rings 9. The shaft 8 is suitably supported for rotation by journal means (not shown) for example. The slip rings 9 connect to the energizing coil 10A of a magnetic clutch 11 which includes an armature plate 12 and a coil retaining plate 10. When the system is in operation a motor 13, which is coupled to armature plate 12 by way of suitable supported shaft 8A, continuously rotates plate 12. As indicated in FIG. 1A shafts 8 and 8A are in line so that the

plates

10 and 12 are in facing concentric relationship to each other. The operation of the magnetic clutch 11 is discussed in more detail hereinafter with reference to FIG. 2.

It is noted that with the driving arrangement, including motor 13, clutch l1, pinion gear 7 and rack 6, the amount of vertical motion which can be applied to the piston is not hampered in any way by the diameter of the casing and the rack 6 may be made as long as necessary for applications acquiring a high compression of the liquid column.

Initially, motor 13 is set in rotation thereby causing armature plate 12 to rotate at the same speed. However, no motion is imparted to plate 10 of magnetic clutch 11 until the coil 10A is energized. To insure that coil 10A is properly and timely energized inertial unit 15 is suitably securely mounted on the top of rack 6 (FIG. 18).

Referring now to FIG. 2, inertial unit 15 includes an outer cylindrical casing 16 having a plunger 17 vertically slideable therein. The plunger 17 is initially held against a stop 18 secured to the upper end of the casing 16 by means of a relatively light spring 19 which has just enough stiffness to press the plunger 17 against the stop 18. Spring 19 is a helical spring and extends from bottom stop 28 to post 17B of plunger 17. It is noted that plunger 17 has opposite frusto-conic ends 17A which smoothly engage the actuating buttons of

switches

20 and 21.

The switches 20 and 21 (see also FIG. 1A) are mounted on the outside of casing 16 on

rings

22 and 23, respectively. These

rings

22 and 23 are adapted to slip over the threaded outer surface 16A of casing 16, and be locked in any given position by means of threaded locking rings 24 and 25 respectively. By means of this arrangement the position of

switches

20 and 21 relative to the plunger 17 can be changed as desired.

The switch 21 shown in FIG. 2 at the lower end of unit 15 is a normally closed switch whereas the switch 20 is a normally open switch. Referring again to FIG. 1A the

switches

20 and 21 along with the plunger 17 are schematically illustrated with the switches in their normal (non-actuated) positions. In the operation of the system motor 13 causes rotation of armature plate 12 of magnetic clutch 11 at a constant speed. When coil 10A is not energized by way of slip rings 9, plate 10 is not caused to rotate. However, when switch 26 is closed a circuit path is provided from one terminal of power supply 27 through normally closed switch 21, switch 26, potentiometer 29, and slip rings 9 to coil 10 and back to the other terminal of supply 27. The actuating voltage from power supply 27 thus causes coil 10 to be energized. When this occurs the armature plate 12 is locked to the coil carrying plate 10 of the clutch 11, and plate 10 starts to rotate with armature plate 12 thus moving rack 6 and piston 5 downward to compress the liquid column 2. Plunger 17 is normally held in an upward position in contact with stop 18 but moves downward as piston 5 descends at substantially the same speed as rack 6. When the downward thrust of the piston becomes insufficient to compress the liquid column much more the descending speed of casing 16 starts to decrease.

When this occurs the plunger 17, being free to move inside the casing 16, continues to descend and its bottom edge 17A actuates the inwardly protruding button of switch 21. The normally closed switch 21 then opens and the voltage from power supply 27 to coil 10 is interrupted. After a short delay time clutch 1l decouples and removes the pressure applied to the top of the liquid column by piston 5. Also, the plunger 17 compresses spring 19 and post 178 eventually moves against stop 28. Thereafter, the liquid column starts to recover toward its initial position of rest. Piston 5 then starts to ascend, as does rack 6 and inertial unit 15. This action keeps plunger 17 in contact with stop 28. However, as the liquid column expands upwardly it tends to go beyond the position of rest and finally comes to rest momentarily in an upward position. As the piston 5 ascends, the plunger 17 tends to maintain its upward velocity. However, when the liquid column decelerates and casing 16 nearly reaches the upper limit of its upward motion, plunger 17 has moved up sufficiently, relative to the casing 16 to allow switch 21 to close and again apply power to coil 10 thereby initiating the next downward thrust of the piston. After a few cycles of operation the oscillation of the liquid column reaches steady state operation at resonance and thereafter the liquid column oscillates at its resonant frequency at an amplitude, and consequently a pumping rate, which is determined at least in part by the amount of current supplied to coil 10. FIG. 1A shows the potentiometer 29 which may be adjusted to control the current suppled to coil 10. The pumped liquid is discharged through outlet opening 4 during each expansion stroke.

Reference has been made herein to the phase of the applied thrust. This phase is the time delay between the time that the resonant liquid column reaches its exact upper limit, and the time that the force is actually applied to the piston to cause the downward thrust. Ideally, this phase difference should be as small as possible. However, it isnot desirable that the motion be imparted to the piston prior to the column reaching its upper limit.

As a practical matter, insofar as the phase of the applied thrust is concerned, there is usually some time delay between the closing of switch 21 at the end of the upward expansion stroke and the actual application of the next downward thrust of the piston 5. As previously stated this downward-thrust should be ideally applied very shortly after the liquid column has reached its upper limit of its expansion stroke and has started downward again. Thus, the actual application of power to coil'10 should occur somewhat ahead of the arrival of the top of the liquid column at its most upward position.

It is the inclusion of switch 20 in the circuit of FIG. 1A and itsposition on casing 16, which is adjustable by means of threaded locking rings 25, that makes it possible to apply power to coil somewhat ahead of the time that the liquid column is at its uppermost position. Switch 20, as indicated in'FIG. 1A is a normally open switch and couples in parallel with switch 21. The closing of switch 20 as plunger 17 ascends in casing 16 automatically applies voltage to coil 10 even though on casing 16 so that the driving thrust is not interrupted until the column has reached the end of its compression stroke.

It should be apparent from the above that the downward velocity of piston 5 imparted to it by motor 13 initially need only be equal to or perhaps slightly greater than the velocity of motion of the liquid column when switch 21 may still be open on the upward stroke of the column. Consequently, by adjusting the position of ring 22, which carries switch 20, upward ordownward on casing 16 the timing of the energization of coil 10 can be adjusted to compensate for time delays in the actual actuation of the clutch. This time delay is caused at least in part by means of clutch l1 and the rack and pinion gear arrangement. If the time delay between the closing of switch 20 and the actual actuation 'of the downward thrust is sufficiently great the voltage may be applied to coil 10 well before the liquid column reaches the top of the expansion stroke by adjusting the position of switch 20 downward to compensate therefore. Alternatively, if there is only a small delay in the application of the downward thrust switch 20 may be moved upward or perhaps even entirely eliminated. Switch 20 could be removed if the closure of switch 21 provided the proper phase.

Similarly, the position of switch 21 is also adjustable by means of varying the upward or downward position of ring 23. For instance, during the downward stroke of the piston the thrust applied thereto can be interrupted somewhat before it reaches the end of the downward stroke to compensate for any time delay in the electrical circuit and clutch. operation. Thus, by moving the switch 21 upwardly relative to casing 16 when the delay is great the switch 21 opens sooner and eliminates any downward pressure that might be exerted on the liquid column even after the column reached the end of its compression stroke-and started to return on the expansion. For shorter delay times switch 21 may be loweredit is oscillating at resonance at the desired amplitude.

Once operation at resonance has been attained the system of the invention automatically keeps the downward power pulses at the desired level and at the proper frequency and phase for most efficient operation.

While only a single embodiment of the present invention has been illustrated herein, other embodiments and modifications thereof are also contemplated as falling within the scope of this invention and should be limited solely 'by the appended claims.

What is claimed is:

1. A resonant column pumping system comprising:

means for establishing a liquid column having a resonant frequency,

pump means for pumping liquid from the top of said column including means for periodically removing a quantity of'liquid from said column upon cyclical expansion of said column at said resonant frequency,

said pump means including means for periodically applying pressure to said column at said resonant frequency,

and means for controlling said pumping means ineluding,

means operatively coupled to said means for periodically applying pressure for sensing the termination of both the expansion stroke and contraction stroke of the liquid column,

and feedback means operatively coupled from said sensing means for interrupting said means for periodically applying pressure when the termination of the contraction stroke is sensed, and for allowing application of the pressure when the termination of the expansion stroke is sensed,

said means for sensing including inertial means and said pressure applying means including a fluid displacement member with said inertial means connected to said displacement member for movement therewith.

2. A resonant column pumping system as set forth in claim 1 wherein said means for establishing includes a well casing for containing the liquid column.

3. A resonant column pumping system as set forth in claim 2 and further comprising one-way valve means at the bottom of the well casing to permit liquid to flow into the well casing, and outlet means at the upper end of the liquid column through which the liquid discharges. t

4. A resonant column pumping system as set forth in claim 1 wherein said pressure applying means includes a piston disposed at the top end of the means for establishing, a rack and pinion gear arrangement with one end of the rack fixed to the top of the piston and the gear suitably supported for rotation in meshing engagement with the teeth of the rack, motor means, and means intercoupling said motor means and said gear, whereby said motor means is capable of causing rotation of said gear which in turn drives said rack and piston in a liquid compressing manner.

5. A resonant column pumping system as set forth in claim 4 wherein said intercoupling means includes an electromechanical clutch means responsively coupled to said feedback means for coupling and decoupling said motor means to and from said gear.

6. A resonant column pumping system as set forth in claim 5 wherein said electromechanical clutch means includes a pair of clutch plates, one connected by means of a first shaft to said motor means and the other connected by means of a second shaft for supporting said gear, said other plate being moveable toward and away from the one plate and including coil means responsively coupled from said feedback means for selectively energizing and deenergizing said coil means thereby respectively coupling and decoupling said plates.

7. A resonant column pumping system as set forth in claim 1 wherein said inertial means includes a casing, an actuating member slideably disposed in the casing, and switch means responsive to the position of the actuating member relative to the casing, wherein said switch means is conditioned to interrupt said pressure applying means when the displacement member is in a lowermost position, and to allow application of the pressure when the displacement member is in an uppermost position.

8. A resonant column pumping system as set forth in claim 7 wherein said casing has an aperture therein and said switch means is fixedly secured to an outer surface of the casing and includes a button having a dimension less than said aperture and extending inwardly therethrough in contactable relation to said actuating member.

9. A resonant column pumping system as set forth in claim 8 wherein said casing has a threaded outer portion and further comprising adjustable ring means mating with said threaded portion for retaining said switch means .at different positions relative to said casing thereby enabling said switch means to be switched to its interrupt condition at different times to compensate for different system delays.

10. A resonant column pumping system as set forth in claim 9 wherein said actuating member includes resilient means for holding said actuating member in an upper position in said casing during the contraction stroke.

11. A resonant column pumping system as set forth in claim 7 wherein said actuating member includes a plunger and said casing has upper and lower stops for limiting the movement of the plunger in the casing, said plunger having at least one inwardly tapered end for contacting a button of said switch means.

12. A resonant column pumping system as set forth in claim 7 and further comprising a second switch means responsive to the position of the actuating member relative to the casing and positioned to cause actuation of the pressure applying means at an earlier time than caused by said first switch means.

13. A resonant column pumping system as set forth in claim 12 wherein said second switch means is fixedly secured to said casing and is adjustable vertically relative thereto.

14. A resonant column pumping system comprising:

means for establishing a liquid column having a resonant frequency,

pump means for pumping liquid from the top of said column including means for periodically removing a quantity of liquid from said column upon cyclical expansion of said column at said resonant frequency,

and means for controlling said pumping means including,

means operatively coupled to said means for periodically applying pressure for sensing the termination of both the expansion stroke and contraction stroke of the liquid column, and feedback means operatively coupled from said sensing means for interrupting said means for periodically applying pressure when the termination of the contraction stroke is sensed, and for allowing application of the pressure when the termination of the expansion stroke is sensed, wherein said means for sensing includes inertial means and switch means responsive to the position of said inertial means, said switch means being in a first position during the expansion stroke and a second position during the contraction stroke,

said feedback means including circuit means and power source means intercoupling said switch means and said pressure applying means for interruption pressure application when said switch means is in the first position and for allowing pressure application when said switch means is in the second position.

15. A resonant column pumping system as set forth in claim 14 wherein said switch means is adjustable relative to said inertial means to provide for actuation of said pressure applying means at the proper resonant frequency and phase of the liquid column.

16. A resonant column pumping system as set forth in claim 14 wherein said circuit means includes a variable potentiometer connected in series with said power source means.

17. A resonant column pumping system as set forth in claim 14 wherein said pressure applying means includes a fluid displacement member with said inertial means connected to said displacement member for movement therewith, and a motor-driven electromechanical clutch coupled to said displacement member for selectively driving said member, said circuit means including conductive means coupled to said clutch for coupling said clutch when said switch means is in the second position and for decoupling said clutch when said switch means is in the first position.

18. A resonant column pumping system as set forth in claim 17 wherein said conductive means includes a slip ring means.

19. A resonant column pumping system as set forth in claim 17 wherein said clutch includes a pair of clutch plates with coil means associated with one of said clutch plates and said circuit means is adapted to selectively energize said coil means.

20. In a resonant column pumping system having means for establishing a liquid column having a resonant frequency and means for pumping liquid from the top of said column to periodically remove a quantity therefrom during the cyclic expansion of said column wherein said pumping means includes means for selectively applying pressure to said column at said resonant frequency, the improvement comprising means for controlling said pressure applying means including;

means operatively coupled to said means for selectively applying pressure for sensing the motion of the pressure applying means to establish a first condition indicative of the expansion stroke associated with the liquid column, and a second condition indicative of the contraction stroke,

and feedback means operatively intercoupling said sensing means and said pressure applying means with relation to the resonant frequency of the column to cause the pressure applying means to be enabled at the uppermost position of the liquid column.

22. In a resonant column pumping system as set forth in claim 21 wherein the pressure applying means is enabled just after the uppermost position of the liquid column is reached.

23. In a resonant column pumping system as set forth in claim 20 wherein said sensing means changes from said second condition to said first condition at a time with relation to the resonant frequency of the column to cause the pressure applying means to be inhibited at the lowermost position of the liquid column.

24. In a resonant column pumping system as set forth in claim 23 wherein the pressure applying means is inhibited just prior to the lowermost position of the liquid column being reached.

Claims

1. A resonant column pumping system comprising: means for establishing a liquid column having a resonant frequency, pump means for pumping liquid from the top of said column including means for periodically removing a quantity of liquid from said column upon cyclical expansion of said column at said resonant frequency, said pump means including means for periodically applying pressure to said column at said resonant frequency, and means for controlling said pumping means including, means operatively coupled to said means for periodically applying pressure for sensing the termination of both the expansion stroke and contraction stroke of the liquid column, and feedback means operatively coupled from said sensing means for interrupting said means for periodically applying pressure when the termination of the contraction stroke is sensed, and for allowing application of the pressure when the termination of the expansion stroke is sensed, said means for sensing including inertial means and said pressure applying means including a fluid displacement member with said inertial means connected to said displacement member for movement therewith.

3. A resonant column pumping system as set forth in claim 2 and further comprising one-way valve means at the bottom of the well casing to permit liquid to flow into the well casing, and outlet means at the upper end of the liquid column through which the liquid discharges.

9. A resonant column pumping system as set forth in claim 8 wherein said casing has a threaded outer portion and further comprising adjustable ring means mating with said threaded portion for retaining said switch means at different positions relative to said casing thereby enabling said switch means to be switched to its interrupt condition at different times to compensate for different system delays.

14. A resonant column pumping system comprising: means for establishing a liquid column having a resonant frequency, pump means for pumping liquid from the top of said column including means for periodically removing a quantity of liquid from said column upon cyclical expansion of said column at said resonant frequency, said pump means including means for periodically applying pressure to said column at said resonant frequency, and means for controlling said pumping means including, means operatively coupled to said means for periodically applying pressure for sensing the termination of both the expansion stroke and contraction stroke of the liquid column, and feedback means operatively coupled from said sensing means for interrupting said means for periodically applying pressure when the termination of the contraction stroke is sensed, and for allowing application of the pressure when the termination of the expansion stroke is sensed, wherein said means for sensing includes inertial means and switch means responsive to the position of said inertial means, said switch means being in a first position during the expansion stroke and a second position during the contraction stroke, said feedback means including circuit means and power source means intercoupling said switch means and said pressure applying means for interruption pressure application when said switch means is in the first position and for allowing pressure application when said switch means is in the second position.

20. In a resonant column pumping system having means for establishing a liquid column having a resonant frequency and means for pumping liquid from the top of said column to periodically remove a quantity therefrom during the cyclic expansion of said column wherein said pumping means includes means for selectively applying pressure to said column at said resonant frequency, the improvement comprising means for controlling said pressure applying means including; means operatively coupled to said means for selectively applying pressure for sensing the motion of the pressure applying means to establish a first condition indicative of the expansion stroke associated with the liquid column, and a second condition indicative of the contraction stroke, and feedback means operatively intercoupling said sensing means and said pressure applying means for inhibiting operation of tHe pressure applying means during said first condition and for enabling operation of the pressure applying means during said second condition, said means for sensing including inertial means coupled to said means for selectively applying pressure for movement therewith.

21. In a resonant column pumping system as set forth in claim 20 wherein said sensing means changes from said first condition to said second condition at a time with relation to the resonant frequency of the column to cause the pressure applying means to be enabled at the uppermost position of the liquid column.