SWITCHING ASSEMBLY FOR A HYDRAULIC PUMP JACK

Abstract

A switching assembly for a hydraulic pump jack has a non-magnetic cylinder. A piston is reciprocally movable within the interior bore of the cylinder. The piston has circumferential sealing means to engage the interior surface of the cylinder. A magnetic element is carried by the piston. A fluid source supplies a working fluid to the cylinder, wherein the piston is moved by injecting working fluid into the cylinder. At least one magnetic sensor is externally mounted adjacent to the non-magnetic cylinder that senses at least a top of a piston stroke and the bottom of the piston stroke. A controller receives signals from the magnetically actuated sensor as the magnet element carried by the piston comes in proximity with and influences the at least one magnetic sensor. The controller controls piston positioning by selectively controlling the working fluid supplied by the fluid source to the cylinder.

Description

FIELD

The present switching assembly is intended for use with a hydraulic pump jack to improve switching by more accurately determining piston position and speed.

BACKGROUND

Switching assemblies presently used for hydraulic pump jacks consist of two axially spaced ports equipped with fittings in which are positioned electric over hydraulic switches. The positioning of these ports determines the upper limit and the lower limit of the piston stroke. The electric over hydraulic switches are tied into an electrically controlled hydraulic spool valve. Variations in hydraulic pressure at the ports results in the switches causing the hydraulic spool valve to reverse the direction and flow of hydraulic working fluid.

SUMMARY

There is provided a switching assembly for a hydraulic pump jack, comprising a non-magnetic cylinder with an exterior surface and an interior surface that defines an interior bore. A piston is reciprocally movable within the interior bore of the cylinder, the piston having circumferential sealing means to engage the interior surface of the cylinder. A magnetic element is carried by the piston. A fluid source supplies a working fluid to the cylinder, wherein the piston is moved by injecting working fluid into the cylinder. At least one magnetic sensor is externally mounted adjacent to the non-magnetic cylinder that senses at least a top of a piston stroke and the bottom of the piston stroke. A controller receives signals from the magnetically actuated sensor as the magnet element carried by the piston comes in proximity with and influences the at least one magnetic sensor. The controller controls piston positioning by selectively controlling the working fluid supplied by the fluid source to the cylinder.

According to another aspect, the cylinder may have a lower end and an upper end with the upper end being higher than the lower end. The working fluid serves to raise the piston from the lower end toward the upper end, and gravity serves to return the piston from the upper end to the lower end.

According to another aspect, the magnetic sensor may be a linear displacement transducer sensor bar that extends along the height of the non-magnetic cylinder.

According to another aspect, the switching assembly may further comprise a seal for sealing the well when the piston is in a lower position, the non-magnetic cylinder being removable to expose the piston in the lower position.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to be in any way limiting, wherein:

FIG. 1 is a perspective view of a switching assembly for a hydraulic pump jack.

FIG. 2 is a side elevation view of the hydraulic pump jack from the switching assembly of FIG. 1.

FIG. 3 is a side elevation view, in section, of the hydraulic pump jack from the switching assembly of FIG. 1.

FIG. 4 is a side elevation view of a piston.

FIG. 5 is a detailed side elevation view, in section, of the piston in a lower, locked position.

DETAILED DESCRIPTION

A switching assembly for a hydraulic pump jack generally identified by reference numeral 10, will now be described with reference to FIG. 1 through 5.

Structure and Relationship of Parts:

Referring to FIG. 1, a switching assembly for a hydraulic pump jack 10 includes a non-magnetic cylinder 12 in combination with a control unit 18 that includes an electronic controller and a hydraulic fluid source (concealed within control unit 18). Referring to FIG. 3, positioned within non-magnetic cylinder 12 is a piston 14. Referring to FIG. 4, a magnetic element 16 is mounted on piston 14. Referring to FIG. 3, an externally mounted magnetically triggered sensor 20 extends along the length of non-magnetic cylinder 12 that is responsive to the position of piston 14. In one example, sensor 20 is a linear displacement transducer (“LDT”) that employs magnetostrictive technology. A magnetostrictive LDT works roughly as follows. An interrogation pulse is transmitted along a waveguide in the sensor bar. When the magnetic field generated by the pulse interacts with the magnetic field of a permanent magnet that is positioned somewhere along the waveguide, a strain pulse is generated and returned back toward the transmitter. The time elapsed between the transmitting the interrogation pulse the receiving the strain pulse is proportional to the distance between the transmitter and the permanent magnet. A processor then converts the elapsed time into an electrical signal that represents the distance between the transmitter and the permanent magnet. In the present example, the LDT sensor bar 20 is mounted on the outside of the lifting cylinder 12 and the permanent magnet 16 is located inside of the cylinder 12, and travels up and down with the polish rod, such as on piston 14 as shown. As the permanent magnet 16 travels up and down, sensor bar 20 measures the distance between the transmitter and the magnet, which relates to the position of piston 14, with an accuracy that may approach +/−0.1″. The electrical output signal representing the position of the polish rod may be updated at much as 300 times per second or more. It will be recognized by those of ordinary skill in the art that other magnetically actuated switches may also be used that determine the position, and sensor 20 may include multiple sensing elements, or multiple types of sensors. If discrete sensors are used, at least two are required: one for the top, and another for the bottom.

Referring to FIG. 1, control unit 18 receives signals from the magnetically triggered sensor 20 and is able to determine the position of piston 14.

Referring to FIG. 2, the non-magnetic cylinder 12 has an exterior surface 24, a lower end 30 and an upper end 32 that is higher than the lower end 30. Referring to FIG. 3, the non-magnetic cylinder includes an interior surface 26 that defines an interior bore 28. Piston 14 is reciprocally movable within the interior bore 28 of the cylinder 12

Referring to FIG. 5, piston 14 has circumferential seals 34 to engage the interior surface 26 of the cylinder 12. Referring to FIG. 1, the hydraulic fluid source within control unit 18 supplies a hydraulic working fluid to the cylinder 12. Referring to FIG. 3, the hydraulic working fluid causes the piston 14 to be raised from the lower end 30 toward the upper end 32 by an injection of working fluid 36 into the cylinder 12. The piston 14 returns from the upper end 32 to the lower end 30 by force of gravity.

Referring to FIG. 3, sensor 20 is mounted to the exterior surface 24 of the cylinder 12 in axially spaced regular intervals. As shown, sensor bar 20 spans the full length of the non-magnetic stainless steel cylinder 12, and an electronic instrument is wired to this sensor bar and reads the signal generated by the magnet in a particular location.

Referring to FIG. 3, magnetically triggered sensor 20 is excited as the magnetic element 16 carried by the piston 14 comes in proximity with either the discrete sensors, or, in the preferred embodiment, as it influences the magnetic field within the LDT bar. This enables the electronic controller within control unit 18 to determine precise piston positioning based upon the unique sensor value of the signals received and control movement of piston 14 by selectively controlling the working fluid supplied to the cylinder 12. In one embodiment, the LDT bar 20 allows the electronic controller to know where the piston is in its travel within 0.1″ inches of movement such that it can adjust the supply of hydraulic fluid to speed up or slow down to the programmed strokes per minute. When sensor 20 is an LDT bar, the stroke length can be programmed to start and stop at any desired location along the length of cylinder 12.

Operation:

In the description below, the embodiment that uses the LDT bar is described. Referring to FIG. 3, hydraulic working fluid supplied by the hydraulic fluid source within control unit 18, enters the cylinder 12 causing the piston 14 to rise towards the upper end 32 of the cylinder 12, away from the lower end 30. As the piston 14 moves upwards, the magnetic element 16 (best shown in FIG. 4) interacts with sensor bar 20. Signals from the LDT sensor bar 20 are sent to an electronic controller within control unit 18. The electronic controller determines precise piston positioning and controls movement by selectively controlled the working fluid supplied to the cylinder 12. At the termination of each stroke, the force of gravity is used to move the piston 14 downwards towards lower end 30 and away from upper end 32.

Advantages:

To increase or decrease the speed of the cylinder with prior art devices is a complicated process of adjusting the flow of the pump and timing the strokes by watching a pressure gauge. When the pressure goes high, the time clock is activated and when the pressure goes low it is stopped. The time elapsed is then used to calculate the speed of the cylinder. This can be a time consuming process, of adjusting and waiting for the desired results.

The systems used previously have many undesirable features. First and foremost is the potential of the hydraulic cylinder to leak at any of the locations along its length where the ports are located. The electric over hydraulic switches are prone to failure, and their life span is very limited due to the fact that they are a mechanical switch. The operator also has to uncouple and recouple these switches manually and put them into the positions required for the desired stroke length. There is also a danger of spilled hydraulic fluid any time this is done.

The preferred system does not require pressure ports through which fluids could leak, and has explosion proof classification in class 1 division 2 areas around the well head, which reduces the risk of well head explosions.

In addition, as the system is completely sealed, piston 14 may be more easily serviced. Referring to FIG. 5, piston 14 is lowered to the lower end 30 of piston cylinder 12 and locked into place using a common wellhead lock or safety valve, such as a blowout preventer 38. As shown, once locked down, the wellbore is sealed, such that cylinder 12 may be removed to allow access to piston 14 without the use of a service rig to hold the weight of the rod string. At this point, piston 14 may be serviced or replaced while keeping the well shut-in and allows the full weight of the string to be held independent of any lifting equipment, while maintaining full containment on the well. The piston design allows the cylinder to be removed without disconnecting the sucker rod, polish rod and exposing the wellhead to the atmosphere. This function allows cost savings and easy servicing.

Most of the hydraulic cylinders presently manufactured use a steel outer tube with steel piston rod and steel piston. In magnetics, it is known that steel acts as a shunt, where the magnetic lines of flux will not pass through steel. The present system is manufactured using non-magnetic materials. For example, in one embodiment, the outer cylinder tube was manufactured using non-magnetic stainless steel, and the piston was manufactured using non-magnetic aluminum and the piston rod was manufactured using high quality steel. The aluminum piston houses may be rare earth neomidium iron boron magnet with high strength magnetic characteristics.

The presently described system enables the operator to know the position and the speed of the hydraulic cylinder within a fraction of an inch, if desired. The preferred embodiment uses and LDT sensor bar that spans the full length of the non-magnetic stainless steel cylinder and enables the user to adjust the hydraulics to speed up or slow down to the programmed strokes per minute. The stroke length can be programmed to start and stop anywhere between various switch points along the length of the hydraulic cylinder to an accuracy of up to 0.1″in some embodiments.

Traditional electric over hydraulic switches used on most hydraulic pump jacks utilize a diaphragm which, when hydraulic pressure pushes against this diaphragm it either opens or closes a mechanical toggle switch. Because of the mechanical nature of this design it is limited to the number of times it can be activated.

In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements.

The following claims are to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, and what can be obviously substituted. Those skilled in the art will appreciate that various adaptations and modifications of the described embodiments can be configured without departing from the scope of the claims. The illustrated embodiments have been set forth only as examples and should not be taken as limiting the invention. It is to be understood that, within the scope of the following claims, the invention may be practiced other than as specifically illustrated and described.

Claims

1. A switching assembly for a hydraulic pump jack, comprising in combination:

a non-magnetic cylinder with an exterior surface and an interior surface that defines an interior bore;

a piston reciprocally movable within the interior bore of the cylinder, the piston having circumferential sealing means to engage the interior surface of the cylinder;

a magnetic element carried by the piston;

a fluid source supplying a working fluid to the cylinder, wherein the piston is moved by injecting working fluid into the cylinder;

at least one magnetic sensor externally mounted adjacent to the non-magnetic cylinder that senses at least a top of a piston stroke and the bottom of the piston stroke;

a controller that receives signals from the magnetically actuated sensor as the magnet element carried by the piston comes in proximity with and influences the at least one magnetic sensor, the controller controlling piston positioning by selectively controlling the working fluid supplied by the fluid source to the cylinder.

2. The switching assembly of claim 1, wherein the cylinder has a lower end and an upper end, the upper end being higher than the lower end, the working fluid serving to raise the piston from the lower end toward the upper end, and gravity serving to return the piston from the upper end to the lower end.

3. The switching assembly of claim 1, wherein the magnetic sensor is a linear displacement transducer sensor bar that extends along the height of the non-magnetic cylinder.

4. The switching assembly of claim 1, further comprising a seal for sealing the well when the piston is in a lower position, the non-magnetic cylinder being removable to expose the piston in the lower position.

5. A switching assembly for a hydraulic pump jack, comprising in combination:

a non-magnetic cylinder with an exterior surface, an interior surface that defines an interior bore, a lower end and an upper end that is higher than the lower end;

a piston reciprocally movable within the interior bore of the cylinder, the piston having circumferential sealing means to engage the interior surface of the cylinder;

a magnetic element carried by the piston;

a fluid source supplying a hydraulic working fluid to the cylinder, wherein the piston is raised from the lower end toward the upper end by an injection of working fluid into the cylinder;

a linear displacement transducer (LDT) sensor bar mounted to the exterior surface of the cylinder, the LDT sensor bar continuously measuring the position of the piston; and

a controller that receives signals from the LDT sensor bar as the magnet element carried by the piston travels along the non-magnetic cylinder, the controller controlling piston movement by selectively controlling the working fluid supplied by the fluid source to the cylinder in response to the received signals.

6. The switching assembly of claim 5, wherein the piston returns from the upper end to the lower end by force of gravity.

7. The switching assembly of claim 5, further comprising a seal for sealing the well when the piston is in a lower position, the non-magnetic cylinder being removable to expose the piston in the lower position.