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Title:
TORQUE IMPACT MITIGATOR FOR POWER TONG
Document Type and Number:
WIPO Patent Application WO/2020/117355
Kind Code:
A1
Abstract:
A torque impact mitigator including a housing assembly having a hydraulic cylinder. A piston is disposed within the hydraulic cylinder. A piston rod is mounted at a first end to the piston and having a second end extending out from the compression end. A compression spring is disposed between the piston and an end of the cylinder. A rod clevis is secured to the second end of the piston rod to compress the compression spring into a compressed state when the rod clevis is moved away from the cylinder and to release the compression spring into a relaxed state when the rod clevis is moved towards the cylinder. A plug is disposed within an upper end of the compression spring and having a bore extending therethrough to receive the piston rod. One or more bores are disposed through the piston to allow passage of hydraulic fluid into the hydraulic cylinder.

Inventors:
DAVIS TRUMAN (US)
Application Number:
US2019/052561
Publication Date:
June 11, 2020
Filing Date:
September 24, 2019
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
DAVIS TRUMAN R (US)
International Classes:
E21B19/16; F16F13/00
Foreign References:
US3072954A1963-01-15
DE102014105025A12015-10-15
US20140352972A12014-12-04
US2311225A1943-02-16
US1836184A1931-12-15
US20180058161A12018-03-01
US7191686B12007-03-20
Attorney, Agent or Firm:
COHN, Howard, M. (US)
Download PDF:
Claims:
In the claims:

1. A torque impact mitigator (10), comprising:

a housing assembly (20) including a hydraulic cylinder (26) having a compression end (26a) and a rebound end (26b);

a piston (44) disposed within the hydraulic cylinder (26) so as to reciprocate back and forth;

a piston rod (28) disposed within the hydraulic cylinder (26) and mounted at a first end to the piston and having a second end extending out from the compression end; a compression spring (60) disposed between the piston (44) and the compression end (22a) of the hydraulic cylinder (26);

a rod clevis (90) secured to the second end of the piston rod (28) to compress the compression spring (60) into a compressed state when the rod clevis is moved away from the hydraulic cylinder and to release the compression spring into a relaxed state when the rod clevis is moved towards the hydraulic cylinder;

a plug (62) is disposed within an upper end (60a) of the compression spring and having a bore (64) extending therethrough to receive the piston rod; and

one or more bores (56) disposed through the piston to allow the passage of hydraulic fluid into the compression end of the hydraulic cylinder when the compression spring is in the compressed state, and to allow the passage of hydraulic fluid into the rebound end of the hydraulic cylinder when the compression spring is in the relaxed state.

2. The torque impact mitigator (10) of claim 1 wherein the housing assembly (20) includes first and second end caps (22, 24), wherein the compression end (26a) of the hydraulic cylinder (26) is secured to the first end cap and the rebound end (26b) of the hydraulic cylinder is secured to the second end cap.

3. The torque impact mitigator (10) of claim 1 wherein the compression spring (60) is disposed about the piston rod (28) and against the piston (44) and against the plug (62).

4. The torque impact mitigator (10) of claim 3 wherein the compression spring (60) has an outer diameter approximately equal to an inner diameter of the hydraulic cylinder (26).

5. The torque impact mitigator (10) of claim 1 wherein:

an underside of the first end cap has a first circular slot (40) surrounding an opening through the first end cap (22) and an underside of the second end cap (24) has a second circular slot (42); and

the first circular slot receives the compression end (26a) of the hydraulic cylinder

(26) and the second circular slot receives the rebound end (26b) of the hydraulic cylinder.

6. The torque impact mitigator (10) of claim 1 wherein the piston (44) has a piston wear ring (48) fitted into a first groove (50) formed about a cylindrical outer surface (44a) of the piston (44) to provide a side load bearing area to prevent scoring of an inner surface

(27) of the hydraulic cylinder (26).

7. The torque impact mitigator (10) of claim 6 wherein a piston seal (52) is fitted into a second groove (54) formed in the cylindrical outer surface (44a) of the piston (44) to provide a positive seal with minimal friction to extend seal operation under high pressure.

8. The torque impact mitigator (10) of claim 1 wherein the plug (62) has an outer cylindrical element (66) which has a diameter that is approximately equal to the inner diameter of the hydraulic cylinder (26).

9. The torque impact mitigator (10) of claim 8 wherein an outer surface (66a) of the plug (62) rests against the inner surface (22a) of the first end cap (22).

10. The torque impact mitigator (10) of claim 8 wherein the plug (62) has an inner cylindrical surface element (62a) which intersects the inner facing surface of the outer cylindrical element (66) and has a diameter that is approximately equal to the inner diameter of the compression spring (60) so that the inner cylindrical surface of the plug can be inserted into a first end (60a) of the spring (60).

11. A torque impact mitigator (10) to be used in conjunction with a power tong on an oil drilling rig, comprising:

the torque impact mitigator (10) is anchored to the drilling rig, whereby a cable is connected at one end to one end of the torque impact mitigator, and on an opposite second end to the power tong;

a second end of the torque impact mitigator is be mounted to a support on the oil well rig.

a housing assembly (20) including a hydraulic cylinder (26) having a compression end (26a) and a rebound end (26b);

a piston (44) disposed within the hydraulic cylinder (26) so as to reciprocate back and forth;

a piston rod (28) disposed within the hydraulic cylinder (26) and mounted at a first end to the piston and having a second end extending out from the compression end; a compression spring (60) disposed between the piston (44) and the compression end (22a) of the hydraulic cylinder (26);

a rod clevis (90) secured to the second end of the piston rod (28) to compress the compression spring (60) into a compressed state when the rod clevis is moved away from the hydraulic cylinder and to release the compression spring into a relaxed state when the rod clevis is moved towards the hydraulic cylinder;

a plug (62) is disposed within an upper end (60a) of the compression spring and having a bore (64) extending therethrough to receive the piston rod; and

one or more bores (56) disposed through the piston to allow the passage of hydraulic fluid into the compression end of the hydraulic cylinder when the compression spring is in the compressed state, and to allow the passage of hydraulic fluid into the rebound end of the hydraulic cylinder when the compression spring is in the relaxed state.

12. The torque impact mitigator (10) of claim 11 wherein the housing assembly (20) includes first and second end caps (22, 24), wherein the compression end (26a) of the hydraulic cylinder (26) is secured to the first end cap and the rebound end (26b) of the hydraulic cylinder is secured to the second end cap.

13. The torque impact mitigator (10) of claim 11 wherein the compression spring (60) is disposed about the piston rod (28) and against the piston (44) and against the plug (62).

14. The torque impact mitigator (10) of claim 13 wherein the compression spring (60) has an outer diameter approximately equal to an inner diameter of the hydraulic cylinder (26).

15. The torque impact mitigator of claim 11 wherein:

an underside of the first end cap has a first circular slot (40) surrounding an opening through the first end cap (22) and an underside of the second end cap (24) has a second circular slot (42); and

the first circular slot receives the compression end (26a) of the hydraulic cylinder (26) and the second circular slot receives the rebound end (26b) of the hydraulic cylinder.

16. The torque impact mitigator (10) of claim 11 wherein the piston (44) has a piston wear ring (48) fitted into a first groove (50) formed about a cylindrical outer surface (44a) of the piston (44) to provide a side load bearing area to prevent scoring of an inner surface (27) of the hydraulic cylinder (26).

17. The torque impact mitigator(lO) of claim 16 wherein a piston seal (52) is fitted into a second groove (54) formed in the cylindrical outer surface (44a) of the piston (44) to provide a positive seal with minimal friction to extend seal operation under high pressure.

18. The torque impact mitigator of claim 11 wherein the plug (62) has an outer cylindrical element (66) which has a diameter that is approximately equal to the inner diameter of the hydraulic cylinder (26).

19. The torque impact mitigator (10) of claim 18 wherein an outer surface (66a) of the plug (62) rests against the inner surface (22a) of the first end cap (22).

20. A method of using a torque impact mitigator in conjunction with a power tong on an oil drilling rig, comprising:

anchoring the torque impact mitigator to the drilling rig with a cable connected at one end a first end of the torque impact mitigator and on an opposite second end to the power tong;

mounting a second end of the torque impact mitigator to a support on the oil well rig;

constructing the torque impact mitigator from a housing assembly including a hydraulic cylinder with a compression end and a rebound end;

disposing a piston within the hydraulic cylinder so as to reciprocate back and forth;

mounting a piston rod at a first end to the piston and extending a second end of the piston rod out from the compression end of the hydraulic cylinder;

compressing the compression spring between the piston and the compression end of the hydraulic cylinder into a compressed state when the piston is moved away from the compression end of the hydraulic cylinder and releasing the compression spring into a relaxed state when the piston is moved towards the rebound end of the hydraulic cylinder;

reducing the buckling of the compression spring from as the spring is compressed with a plug having a bore extending therethrough disposed within an upper end of the compression spring; and

causing the passage of hydraulic fluid through one or more bores in the piston into the compression end of the hydraulic cylinder when the compression spring is in the compressed state and causing the passage of hydraulic fluid through the one or more bores in the piston into the rebound end of the hydraulic cylinder when the compression spring is in the relaxed state.

Description:
TORQUE IMPACT MITIGATOR FOR POWER TONG

FIELD OF INVENTION

[01] The present invention relates generally to a torque impact mitigator and in particular to a torque impact mitigator to be used in conjunction with a power tong on an oil drilling rig.

BACKGROUND OF INVENTION

[02] In the drilling and completion phases in exploring for oil and gas, pipe tongs have been utilized for engaging lengths of casing, drill or completion pipe, known generally as tubular members, end to end, by rig floor personnel operating power tongs directly and in close proximity to the tubulars on the rig floor. A typical casing power tong comprises a set of jaws to make up or break up the joint. The power tongs may weigh a few thousand pounds and are usually supported from the rig by a cable that allows the power tong to be moved manually by the rig floor personnel to engage the pipe, or disengage from the pipe, and be positioned away from the pipe string, to allow other work to proceed. The power tong is connected on the one end to the rig cable.

[03] However, because of the size of the power tongs, more than a single individual, often times two or three men, are required to move the tong into position, and operate the tong to make up or break the joint, and then to manually swing the tong, hanging from the cable, out of the way, and engage it in a position away from the pipe, so that the rig personnel can proceed to other chores. This manual operation of the tong in and out of position must be done with care, since the tong, swinging free from the cable, may strike one of the workers, or inadvertently disengage from Its position and injure workers or damage materials on the rig floor. SUMMARY OF THE INVENTION

[04] According to an embodiment of the present invention, there is disclosed a torque impact mitigator. The torque impact mitigator includes a housing assembly including a hydraulic cylinder having a compression end and a rebound end. A piston is disposed within the hydraulic cylinder so as to reciprocate back and forth. A piston rod is disposed within the hydraulic cylinder and mounted at a first end to the piston and having a second end extending out from the compression end. A compression spring is disposed between the piston and the compression end of the hydraulic cylinder. A rod clevis is secured to the second end of the piston rod to compress the compression spring into a compressed state when the rod clevis is moved away from the hydraulic cylinder and to release the compression spring into a relaxed state when the rod clevis is moved towards the hydraulic cylinder. A plug is disposed within an upper end of the compression spring and having a bore extending therethrough to receive the piston rod. One or more bores is disposed through the piston to allow the passage of hydraulic fluid into the compression end of the hydraulic cylinder when the compression spring is in the compressed state, and to allow the passage of hydraulic fluid into the rebound end of the hydraulic cylinder when the compression spring is in the relaxed state.

[05] Further according to an embodiment of the present invention, there is disclosed a torque impact mitigator to be used in conjunction with a power tong on an oil drilling rig. The torque impact mitigator is anchored to the drilling rig, whereby a cable is connected at one end to one end of the torque impact mitigator, and on an opposite second end to the power tong. A second end of the torque impact mitigator is be mounted to a support on the oil well rig. A housing assembly includes a hydraulic cylinder having a compression end and a rebound end. A piston is disposed within the hydraulic cylinder so as to reciprocate back and forth. A piston rod is disposed within the hydraulic cylinder and mounted at a first end to the piston and having a second end extending out from the compression end. A compression spring is disposed between the piston and the compression end of the hydraulic cylinder. A rod clevis is secured to the second end of the piston rod to compress the compression spring into a compressed state when the rod clevis is moved away from the hydraulic cylinder and to release the compression spring into a relaxed state when the rod clevis is moved towards the hydraulic cylinder. A plug is disposed within an upper end of the compression spring and having a bore extending therethrough to receive the piston rod. One or more bores are disposed through the piston to allow the passage of hydraulic fluid into the compression end of the hydraulic cylinder when the compression spring is in the compressed state, and to allow the passage of hydraulic fluid into the rebound end of the hydraulic cylinder when the compression spring is in the relaxed state.

[06] According to another embodiment of the present invention, there is disclosed a

method of using a torque impact mitigator in conjunction with a power tong on an oil drilling rig. The method includes anchoring the torque impact mitigator to the drilling rig with a cable connected at one end a first end of the torque impact mitigator and on an opposite second end to the power tong. Then, mounting a second end of the torque impact mitigator to a support on the oil well rig.

Constructing the torque impact mitigator from a housing assembly including a hydraulic cylinder with a compression end and a rebound end. Disposing a piston within the hydraulic cylinder so as to reciprocate back and forth. Mounting a piston rod at a first end to the piston and extending a second end of the piston rod out from the compression end of the hydraulic cylinder. Compressing the compression spring between the piston and the compression end of the hydraulic cylinder into a compressed state when the piston is moved away from the compression end of the hydraulic cylinder and releasing the compression spring into a relaxed state when the piston is moved towards the rebound end of the hydraulic cylinder. Reducing the buckling of the compression spring from as the spring is compressed with a plug having a bore extending therethrough disposed within an upper end of the compression spring. Finally, causing the passage of hydraulic fluid through one or more bores in the piston into the compression end of the hydraulic cylinder when the compression spring is in the compressed state and causing the passage of hydraulic fluid through the one or more bores in the piston into the rebound end of the hydraulic cylinder when the compression spring is in the relaxed state. BRIEF DESCRIPTION OF THE DRAWINGS

[07] The structure, operation, and advantages of the present invention will become further apparent upon consideration of the following description taken in conjunction with the accompanying figures (Figures). The figures are intended to be illustrative, not limiting.

[081 Certain elements in some of the figures may be omitted, or illustrated not-to-scale, for illustrative clarity. The cross-sectional views may be in the form of slices, or near sighted cross-sectional views, omitting certain background lines which would otherwise be visible in a true cross-sectional view, for illustrative clarity.

[09] Often, similar elements may be referred to by similar numbers in various figures

(Figures) of the drawing, in which case typically the last two significant digits may be the same, the most significant digit being the number of the drawing figure (Figure).

[010] FIGURE 1 is a front, three-dimensional view of a torque impact mitigator in use with a power tong, according to the present invention.

[Oi l] FIGURE 2 is a front, three-dimensional view of a torque impact mitigator, according to the present invention.

[012] FIGURE 3 is a front, three-dimensional exploded view of the torque impact mitigator, according to the present invention.

[013] FIGURE 4 is a front, three-dimensional view of a spring disposed about a piston

rod mounted to a piston, according to the present invention.

[014] FIGURE 5 is a side, cross-sectional view of the torque impact mitigator in a

contracted condition, according to the present invention.

[015] FIGURE 6 is a side, cross-sectional view of the torque impact mitigator in an expanded condition, according to the present invention.

[016] FIGURE 6A is a side three-dimensional view of the piston, the piston seal, and the piston ring, according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[017] In the description that follows, numerous details are set forth in order to provide a thorough understanding of the present invention. It will be appreciated by those skilled in the art that variations of these specific details are possible while still achieving the results of the present invention. Well-known processing steps are generally not described in detail in order to avoid unnecessarily obfuscating the description of the present invention.

[018] In the description that follows, exemplary dimensions may be presented for an

illustrative embodiment of the invention. The dimensions should not be interpreted as limiting. They are included to provide a sense of proportion. Generally speaking, it is the relationship between various elements, where they are located, their contrasting compositions, and sometimes their relative sizes that is of significance.

[019] In the drawings accompanying the description that follows, often both reference numerals and legends (labels, text descriptions) will be used to identify elements. If legends are provided, they are intended merely as an aid to the reader, and should not in any way be interpreted as limiting.

[020] In drilling a well, a drill string is used. The drill string can comprise a drill bit

attached to sections of drill pipe. As the well is drilled, additional sections of drill pipe are added to the drill string to extend its length until the well is drilled deep enough to reach a formation where substances, such as water, oil or gas, can be extracted from the well. Sections of pipe are joined together using threaded connections on the pipe, often referred to as“pin” and“box”, where the pin of one section of pipe is threaded into the box of an adjoining section of pipe. The drill string is rotated to turn the drill bit in a wellbore in order to drill the well. When the drill string is removed from the wellbore, the sections of pipe are typically removed from the drill string one or more sections at a time. [021] To make or break the threaded connection between sections of pipe, a power tong device can be used to do so. Known designs use a motor with a transmission to operate the power tong mechanism which grips and turns one section of pipe relative to an adjacent section of pipe. As one pipe rotates with respect to the adjacent section of pipe, the two sections of pipe are threaded together or unthreaded so that the two sections of pipe can be separated from each other.

[022] When "breaking a joint" also know as unthreading the two lengths of pipe, the power tong uses shifts into a lower gear of the transmission to increase the torque applied to a first length of pipe being turned to a level required to break the joint. Then, after the joint is broken, the power tong is shifted to a higher gear of the transmission causing an increase in the rotational speed of the first length of pipe being turned to unthread the first length of pipe from the second length of pipe and thus break the connection. When a making a joint between the two lengths of pipe, the higher gear is first used to start the threaded connection by rotating a first length of pipe at a relatively high rotational speed. Then, the transmission is shifter into a lower gear to increase the torque applied to a first length of pipe being turned to a level required to make the joint so that the first and second lengths are firmly connected together.

[023] Figure 1 illustrates a three dimensional, front view of a torque impact mitigator 10, to be used in conjunction with a power tong 12 on an oil drilling rig 14. The torque impact mitigator 10 is anchored to the drilling rig 14. A cable 16 is connected at one end 16a to one end 10a of the torque impact mitigator 10, and on an opposite second end 16b to the power tong 12. A second end 10b of the torque impact mitigator 10 can be mounted to a support 13 of an oil well rig. The power tong 12 is typically suspended from the oil drilling rig by a cable 18. The torque impact mitigator 10 reduces rotation torque impact of the power tong 12 and holds the power tong in position with respect to the pipes or tubulars being connected to each other or disconnected from each other.

[024] Typically, there are several types of pipe or tubulars 17 screwed together one piece to another, end to end, until the entire number of sections of pipe required for the job are joined together and run into the ground below the rig floor. Even through the pipes 16 being formed into a casing string are often formed of steel, when they are screwed together, care has to be taken, especially when the torque is increased to ensure a tight connection, to stop the rotation without the power tong tightening too much because of the inertia. When this occurs, the sleeves interconnecting the adjacent sections of pipe can be damaged.

[025] Figure 2 is a front, three-dimensional view of the torque impact mitigator 10. The torque impact mitigator 10 includes a housing assembly 20, comprising a first end cap 22 and second end cap 24, and a tube or cylinder 26 that is secured between the first end cap 22 and second end cap 24. A piston rod 28 extends out from the first end cap 22 and is threaded to a rod clevis 30. The first and second end caps 22 and 24 are secured to opposite ends of the tube or cylinder 26 by four tie rods 32a, 32b, 32c, and 32d to form housing assembly 20 or any applicable cylinder.

[026] Referring to Figure 3, each of the four tie rods 32a, 32b, 32c, and 32d extends at a first end through an opening 34a, 34b, 34c, and 34d, respectively, in the second end cap 24, and at a second opposite end through an opening 36a, 36b, 36c, and 36d, respectively, in the first end cap 22. Further, the first end cap 22 has an opening 38 through which the piston rod 28 extends. Surrounding the first opening 38 and disposed on the underside of the first end cap 22 is a first circular slot 40, see Figure 5, that is designed to receive a first or compression end 26a of hydraulic cylinder 26. Similarly, the second end cap 24 has a second circular slot 42 disposed on the underside of the second end cap, see Figure 5, that is designed to receive a second or rebound end 26b of hydraulic cylinder 26. It must be noted that any size or shape hydraulic cylinder may be used, depending on the application.

[027] The torque impact mitigator 10 contains a piston 44 disposed within the

hydraulic cylinder 26 so as to reciprocate back and in the cylinder. The piston 44 has one end 28a of the piston rod secured thereto, typically by a threaded connection, within a threaded opening 44a within the piston 44. As shown in FIG. 6A, a piston wear ring 48 is fitted into a first groove 50 formed in the cylindrical surface 44a of the piston 44. The piston wear ring 48 provides a side load bearing area to prevent scoring of the inner surface 27 of the hydraulic cylinder 26. A piston seal 52 is fitted into a second groove 54 formed in the cylindrical outer surface 44a of the piston 44. The piston seal 52 can be for example, an o-ring expander which provides a positive seal with minimal friction to extend the seal operation under high pressure.

[028] The piston 44 can have a one or more bores 56 extending therethrough. While two bores 56a and 56b are illustrated, it is within the scope of the invention to use as few as one bore and as many as needed, such as for example six or eight bores.

[029] Referring to Fig. 4, a compression spring 60 is disposed about the piston rod 28 and has an outer diameter approximately equal to the inner diameter of the

hydraulic cylinder 26. A plug 62 is disposed within the upper end 60a of the spring 60. The plug 62, as shown in Figure 3, has a bore 64 extending therethrough to receive piston rod 28. The plug 62 has an outer cylindrical element 66 which has a diameter that is approximately equal to the inner diameter of the

hydraulic cylinder 26. The outer surface 66a of the plug 62 rests against the inner surface 22a of the first end cap 22. The plug 62 has an inner cylindrical surface element 62a which intersects the inner facing surface of the outer cylindrical element 66 and has a diameter that is approximately equal to the inner diameter of the spring 60 so that the inner cylindrical surface 62a of the plug 62 can be inserted into a first end 60a of the spring. An opposite end 60b of the spring 60 rests against the outer surface 44a of the piston 44.

[030] One end 28b of the piston rod 28 is threaded and secured to a threaded opening 68 through the base 70 of a u-shaped rod clevis 72. Holes 74 and 75 through the ends of the prongs 76 and 78 of the clevis 72 have a clevis pin 80 extending therethrough. A cross hole 82 receives a split pin 84 to secure the clevis pin in place. The tang 16b of a cable 16, as shown in Figure 1, is held in place by the clevis pin 80. [031] The second end cap 24 has a u-shaped rod clevis 90 secured thereto. Holes 92 through the ends of the prongs 94 and 96 of the clevis 90 have a clevis pin 98 extending therethrough. A cross hole in the clevis pin 98 receives a split pin to secure the clevis pin 98 in place. The tang 104 can be mounted to a member 13a of the oi l well member 13 and held in place by the pin 98.

[032] The hydraulic cylinder 26 has piston member 44 normally biased by spring 60 toward the one end of the internal volume of cylinder 26. The piston 44 follows the piston rod 57 due to the pushing force of the spring 60. The coil-shaped spring 61 is installed in such a state that it is compressed between the piston rod 49 and the compression end 22a of cylinder 22.

[033] The torque impact mitigator 10 has a hydraulic fluid charged into the

hydraulic cylinder 26. The spring 60 is installed to normally bias the piston 44 against the second end cap 24 and aid in impact mitigation, as shown in FIG. 5. The piston 44 is retained on the end of piston rod 28 by a threaded connection. The piston 44 generally subdivides the internal volume of hydraulic cylinder 26 into a compression volume located between piston 44 and the compression end 26a of cylinder 26, and a rebound volume located between piston 44 and the rebound end 22b of the cylinder 26.

[034] The movement of the piston 44 toward the compression end 26a of cylinder 26, as shown in FIG. 6, results in a reduction in the size of compression volume in the compression end of the cylinder, and the subsequent flow of hydraulic fluid through bores 56a and 56b of the piston 44. The movement of the piston 44 toward the compression end 26a simultaneously enlarges the rebound volume in the cylinder 26 between the piston 44 and the rebound end 26b. As piston 44 moves towards the compression end 26a of cylinder 26, the spring 60 compresses and slows the movement of the piston 44 which in turn slows the movement of the rod clevis 72 out of the cylinder. The effect is to mitigate the movement of the device 12, such as a power tong as shown in FIG. 1, secured to the rod clevis 72 causing the piston 44 to pull out of the cylinder 26.

[035] The spring 60 normally biases the piston member 44 towards the rebound end 26b of the internal volume of cylinder 26, as shown in FIG. 5. As the u-shaped rod clevis 72 is moved away from the compression end 26a of the hydraulic cylinder 26, the spring contracts and develops increases a greater and greater force on the piston member 44 towards the rebound end 22b of the cylinder 22. The plug 62 limits the compression of the spring 60 and insures that the spring does not buckle as the spring is compressed.

[036] Once the force pulling the u-shaped rod clevis 72 away from the compression

end 22a of cylinder 22 is removed, the spring 60 forces the piston 44 towards the rebound end 22b of the internal volume of cylinder 22 and back to an unloaded location at the bottom end 26b of the cylinder 26. As mentioned before, the movement of the piston 44 back to its initial location will be slowed by the flow of hydraulic fluid in the rebound volume through bores 56a and 56b of the piston 44 and into the compression volume in the compression end of the cylinder 26. The flow of hydraulic fluid through bores 56a and 56b of the piston 44 results in the increase of the volume of hydraulic fluid in the compression volume in the compression end while simultaneously decreasing the volume of hydraulic fluid in the rebound volume in the rebound end of the cylinder.

[037] The effect of this change in the compression volume of hydraulic fluid in the

compression end and while simultaneously decreasing the rebound volume of hydraulic fluid in the rebound end of the cylinder 76 is to mitigate or slow down the movement of the device, such as a power tong, to prevent damage to the tubular being joined together.

[038] The spring 60 biases the piston member 44 towards the rebound end 22b of the

internal volume of cylinder 22. As the u-shaped rod clevis 72 is moved away from the compression end 22a of cylinder 22 of the hydraulic cylinder 26, the spring contracts and increases a greater and greater force on the piston member towards the rebound end 22b of the cylinder 22. The plug 62 limits the compression of the spring 62 and insures that the spring does not buckle as the spring is compressed. Once the force pulling the u-shaped rod clevis 72 away from the compression end 22a of cylinder 22 is removed, the spring forces the piston 44 towards the rebound end 22b of the internal volume of cylinder 22.

[039] The bores 56a and 56b through piston 44 allows the hydraulic fluid to move between the compression volume located between piston 44 and the compression end 26a of cylinder 22, and the rebound volume located between piston and the rebound end 22b of the cylinder 22. The size of the bores 56a and 56b in conjunction with the viscosity of the selected hydraulic fluid controls the speed of the piston as it moves in the cylinder. The effect of controlling the speed that the piston is to mitigate the movement of the device, i.e. the power tongs, attached to the compression end of the hydraulic cylinder 26.

[040] Although the invention has been shown and described with respect to a certain

preferred embodiment or embodiments, certain equivalent alterations and modifications will occur to others skilled in the art upon the reading and

understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, etc.) the terms (including a reference to a "means") used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary

embodiments of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several embodiments, such feature may be combined with one or more features of the other embodiments as may be desired and advantageous for any given or particular application.