US3610502A

US3610502A - Gripper retractor

Info

Publication number: US3610502A
Application number: US17248A
Authority: US
Inventors: Dale H Pryor
Original assignee: Youngstown Sheet and Tube Co
Current assignee: Oil States Industries Inc
Priority date: 1970-03-06
Filing date: 1970-03-06
Publication date: 1971-10-05
Anticipated expiration: 1988-10-05

Abstract

A retractor is provided with a fluid system for opening and closing grippers in which a three-position valve is utilized with a high- and low-pressure system in such manner that fluid from an opening gripper is utilized to close another gripper. The threeposition valve is rotated between open, close and grip position by cooperating lugs carried on the valve and positioned on the retractor.

Description

United States Patent Dale H. Pryor Houston, Tex.

Mar. 6, 1970 Oct. 5, 19-71 Youngstown Sheet and Tube Company Youngstown, Ohio Inventor Appl. No. Filed Patented Assignee GRIPPER RETRACTOR 21 Claims, 8 Drawing Figs.

[56] References Cited UNITED STATES PATENTS 2,892,535 6/1959 Cullen 226/173 3,330,459 7/1967 Cullen 226/173 Primary Examiner-Richard A. Schacher Att0rneys-J. Vincent Martin, Joe E. Edwards, M. H. Gay,

Alfred 1-1. Evans and Jack R. Springgate ABSTRACT: A retract'or is provided with a fluid system for opening and closing grippers in which a three-position valve is utilized with a highand low-pressure system in such manner that fluid from an opening gripper is utilized to close another gripper. The three-position valve is rotated between open,

close and grip position by cooperating lugs carried on the valve and positioned on the retractor.

PATENTED um 5:91:

SHEET 2 [IF 4 fla/e Pryor INVENTOR.

AffO/P/VE )J PATENTED 0m 5 I971 SHEET 3 [IF 4 GRIPPER RETRACTOR In Cullen U.S. Pats. Nos. 2,892,535 and 3,330,459, retractor apparatus is shown for handling flexible pipe during drilling operation. In US. Pat. No. 2,892,535, there is disclosed a fluid system for opening and closing the grippers in which a four-way valve is shifted to either pressurize or exhaust the gripper systems.

Using a pressure and exhaust system results in a relatively large amount of high-pressure fluid flowing through the system to operate the grippers. Desirably, the volume of highpressure fluid flowing through the system is held to a minimum.

An object of this invention is to provide a fluid system for a retractor of the type disclosed in the above-identified Cullen Patents, in which the amount of high-pressure fluid necessary to operate the gripper is held to a minimum.

In accordance with this invention, a fluid system having a highand low-pressure side which is controlled by a threeposition valve is utilized to actuate grippers to open, close and grip positions. The fluid system substantially reduces the volume of high-pressure fluid necessary to handle the gripper system as compared with the above-identified Cullen Patents. This system utilizes a three-position valve associated with each gripper assembly which is moved between open, close and grip position during each revolution of the endless chain.

An object of this invention is to provide a simple economical system for shifting a rotary valve between three positions while the rotary valve is moving along an endless track in either direction.

Another object is to provide a valve-operating system as in the preceding object, in which the number of valves which are in grip position may be varied so that a lower group of grippers may remain open at the lower end of the endless chain during certain pipe-handling operations. Another object is to provide an operating system for retractor grippers which includes a three-position valve in which the valve rotator is resiliently biased by an overcenter system which will assist in moving the valve rotator to an extreme position.

Another object is to provide a control system for a threeposition rotary valve associated with a gripper assembly of a retractor system, in which the valve is oscillated between grip, close and open positions with the endless chain of the retractor running in either direction.

Other objects, features and advantages of the invention will be apparent from the drawings, the specification and the claims.

In the drawings wherein illustrative embodiments of this invention as shown and wherein like reference numerals indicate like parts;

FIG. 1 is a side view in elevation of the retractor portion of a drilling rig;

FIG. 2 is a view taken along the lines 2-2 of FIG. 1 showing the retractor in front elevation;

FIG. 3 is a fragmentary view of one leg of the retractor and showing a portion of the trip mechanism for operating the valves;

FIG. 4 is a view illustrating operation of the three-position valve including the lower trip mechanism, a fragment of the endless chain and one gripper assembly, and the upper trip assembly with the valve rotator shown in dashed lines in conjunction with each of the trip mechanisms;

FIG. 5 is a view along the lines 5-5 of FIG. 4 showing one trip assembly in elevation and a valve rotator passing thereby in dashed lines;

FIG. 6 is a schematic flow diagram illustrating the fluid system for operating the grippers and the assist piston for the valve rotator;

FIG. 7 is an isometric view of the rotor of one of the threeposition valves;

FIG. 8 is a diagrammatic view of a modified form of valve rotator and trip assemblies.

Referring first to FIG. 1, a base, indicated generally at 10, may be supported on a suitable substructure (not shown) over the site of the well to be drilled. This base supports a mast, including legs 11 and 12. Sprockets 13, 13a, 14, and 14a are provided at the upper and lower ends of the mast. The endless chain, indicated generally at 15, is trained over the four sprockets, in the manner taught in the Cullen Patents.

Alternate chain links 16 are carried on a pair of

trunnions

17 and 18 on a gripper assembly. (FIG. 4)

Each gripper assembly may include one or more sets of opposed grippers. Preferably, two sets of opposed grippers are carried on each assembly.

Each gripper assembly is controlled by a single three-position valve, indicated generally at 23, so that the pressure acting on grippers 34 of each assembly is the same.

Reference is made to FIG. 6 wherein the operation of the grippers in accordance with this invention is illustrated. It will be understood that the opening and closing functions take place adjacent to sprockets, while the gripping function takes place during the passage of a gripper assembly vertically between spaced sprockets on the front side of the rig. While fluid is directed to only one cylinder in the schematic of FIG. 6, such fluid will actually be directed to all of the cylinders of each assembly in the manner taught in the above-identified Cullen Patents.

As shown in FIG. 6, each gripper 34 is connected to a pressure responsive member or piston 35 by a suitable connecting rod 36. Preferably, this connecting rod is relatively large in diameter so that there is a substantial difference in the pressure responsive surface or area on the rod side and on the other side of the piston 35. Fluid is directed to and from the cylinder 37, in which the piston 35 reciprocates through

suitable conduits

38 and 39 from the three-position valve indicated generally at 23.

The fluid circuit for operating the grippers includes a highpressure side and a low-pressure side. The high-pressure side includes a manifold line, indicated generally at 41, which is preferably a continuous or closed line. Connected to the line through a suitable swivel 42 is a tank 43 or source of fluid, preferably liquid, which is supplied to the high-pressure manifold 41 by a pump 44. Preferably, the pump will maintain a selected pressure within the manifold line 41 at all times.

Branch lines 45 connect the high pressure manifold 41 with the three-position valves 23 through suitable check valves 46. These check valves prevent back flow of fluid in the event of a failure in the system, a shutdown of the pump or the like, so that the system is failsafe and the grippers will be maintained in gripping relationship with the pipe until the three-position valve is shifted to release the gripping action.

The fluid circuit also includes a low-pressure side, that is selected pressure lower than the pressure in the high-pressure side. This low pressure is maintained in a suitable closed manifold conduit 47 which is connected through branch 48 to the three-position valves 23. The fluid from the low'pressure circuit is returned to tank 43 through the swivel 49.

The selected lower pressure is maintained in the low pressure side of the circuit by the back pressure valve indicated generally at 51. This back pressure valve maintains the desired lower pressure and permits excess fluid to pass into the tank 43 through the outlet line 52.

Preferably, an accumulator 53 is provided in the circuit upstream of the back pressure valve. This accumulator will accumulate fluid from the opening of one gripper assembly and use such accumulated fluid to close another gripper assembly without the necessity of having one gripper assembly open at exactly the same time that another gripper assembly closes.

The three-position valve 23 has one position in which the piston moves the gripper towards closed position. In this position the low-pressure side of the circuit is connected to both sides of the piston 35. As the connecting rod 36 effectively reduces the pressure responsive area of the piston on the rod side, the gripper is moved towards closed position. The lowermost valve 23 is shown in this relationship with the inlet conduit 45 blocked off and the low pressure branch conduit 48 connected to both

lines

38 and 39.

The three-position valve means also has a second position which connects the low pressure side through

lines

48 and 38 to the rod side of the piston 35. The high-pressure side of the circuits, connected through

lines

45 and 39 to the other side of the piston, urges the gripper towards close position under high pressure. This is the gripping relationship and is shown in the middle of the figure.

At the top of the figure there is shown the third position of the three-position valve means, in which the rod side of the piston is connected to the high-pressure side through

lines

38 and 45. The other side of the piston is connected to the lowpressure side of the circuit by connecting

lines

39 and 48. This moves the gripper towards open position.

lt will be apparent that the relative effective areas of the piston and the differential in pressure should be correlated so that the force exerted by the high-pressure fluid on the small area of the rod side of the piston is sufficient to overcome the lower pressure on the larger area on the other side of the piston and move the piston to open position.

There are a number of the gripping assemblies on the endless chain. They are constantly opening and closing. If they were timed to open and close at exactly the same instant, the fluid from the opening assembly could be used to close a closing assembly. By providing the accumulator 53, it is not necessary that the opening and closing of two assemblies be exactly timed as the fluid pressure will be maintained in the accumulator 53 to close the assemblies as the valve is shifted to closing position.

As the fluid from an opening gripper is utilized to close another gripper under low pressure, very little additional fluid need be introduced into the system to close each gripper. Once closed the gripper cylinder is subjected to high pressure fluid, but as hydraulic fluid will be utilized, only a slight amount of additional fluid will be introduced in the cylinder 37 to grip the pipe. During the opening of the gripper, a small amount of high-pressure fluid is utilized, but as the connecting rod is relatively large in size the amount of fluid necessary for this purpose is kept at a minimum. By transferring low-pressure fluid from the opening cycle to the closing cycle, the small amount of additional high-pressure fluid introduced during gripping and opening is suflicient to maintain the fluid flow to the low-pressure side. Thus, it will be seen that the amount of high-pressure fluid flow necessary to operate the grippers has been substantially reduced by this invention, and it is not necessary to design the system to handle large volumes of high-pressure fluid.

The valves 23 are shown schematically. Any type valve may be used. Preferably, they are rotary valves which minimize leakage problems.

FIG. 4 shows the valve rotator for the three-position valve 23 and the associated trip assemblies for moving the valve between its three positions. The gripper assembly housing, indicated generally at 61, carries the two

trunnions

17 and 18 which make up a portion of the endless chain. A pair of such gripper assemblies 61 is shown in FIG. 2. As in the case of the above-identified Cullen Patents, it is preferred that the flow passageways for operating the grippers be internally of the housing, and the valve 23 is mounted on the housing of the gripper assembly 61, as shown in H0. 4, to establish communication between the passageways 38 and 39 (FIG. 6) which lead to the opposite ends of the cylinder 37 for each gripper.

The valve is of the rotary type and rotates about the central axis of shaft 62.

Nonrotatably mounted on shaft 62 is a valve rotator. This rotator has a plurality of lugs which cooperate with the trip assemblies, indicated generally at 63 and 64, to move the valve actuator between open, grip and close position. The valve rotator and the lugs thereon cooperate with the two trip assemblies to move the rotator to close position as it moves into contact with either of the trip assemblies. The valve rotator stays in this position for a short distance to permit fluid to flll the backside of cylinder 37 to close the gripper. Then a lag on the rotator contacts a lug on the trip assembly to move the valve rotator to grip position. The rotator remains in this position as the gripper assembly travels between the two trip assemblies. Upon reaching the second trip assembly, a lug on the rotator engages the second trip assembly which returns the valve rotator to close position. This is essentially a nonfunction position, but in order that the system may function with the endless chain moving in either direction it is simpler to return the valve actuator to close position. As the valve actuator leaves the second trip assembly, lugs are engaged which move the actuator to the open position. In other words, the valve actuator oscillates from open to close to grip position and then back to first close and then open position.

In the preferred form, as shown in FIGS. 4 and 5, the valve actuator has pairs of lugs on opposite sides of the rotator. Thus, lug 65 is on the opposite side of the rotator from lug 66. Another pair of

like lugs

67 and 68 are positioned on opposite sides of the rotator. The lugs 65 through 68 are spaced circumferentially from each other about the rotator. As best shown in FlG. 5, lugs 65 and 66 rotate in a first plane of rotation of the rotator. The

lugs

67 and 68 rotate in a second plane of rotation of the rotator. Preferably, the

lugs

65 and 66 are carried on rotator section 69, and the

lugs

67 and 68 are carried on rotator section 70. By reference to FIG. 5, it will be noted that these two rotator sections are spaced along the axis of shaft 62 and rotate in separate parallel planes.

While valves having different degrees of rotation may be utilized, the illustrated valve is rotatable through approximately and such rotation is limited by lug 67 moving between

stops

71 and 72. It will be noted that lugs 65 and 67 are spaced apart approximately the same distance as

lugs

66 and 68, that is slightly less than 90. This relationship is preferred for cooperation with the lugs of the trip assemblies.

Each trip assembly includes a pair of lugs at opposite ends for engagement with the rotator lugs. Thus, referring to FIG. 5, the end surface 73 and the end surface 74 of the trip assembly each provide a lug for engagement with a rotor lug. The face of the trip assembly 75, which confronts the valve rotator, is planar for a purpose which will be explained hereinafter.

Lugs

76 and 77 extend outwardly from this planar surface 75 toward the valve rotator. it will be noted that the

lugs

76 and 77 are positioned on opposite sides of the upper trip assembly 64 with the lug 76 lying in the path of travel of rotator section 70, and the lug 77 lying in the path of travel of the rotator section 69. The two trip assemblies are identical: therefore, the parts thereof have been given the same numbers. The two trip assemblies only differ in their positioning, that is they face inopposite directions. Thus, the lower trip assembly lug 76 lies in the path of rotator section 69. The lower trip assembly 63 cooperates with

lugs

65 and 67 to shift the valve rotator and the upper trip assembly 64 cooperates with

lugs

66 and 68 to rotate the valve rotator.

Due to the 90rot'ation of the valve 23 in movement between its three positions, it is desirable to utilize the above described assembly to move the valve rotator to its intermediate position but in moving to the two extreme positions it is preferred that the lugs be assisted by additional means.

To assist the rotator in movement to its full extreme positions, an over center resilient means is provided, which when moved to either side of center, exerts a resilient force on the valve rotator to assist the lugs in moving the valve rotator to its two extreme positions. This resilient means may take any desired form, such as the fluid cylinder indicated generally at 78. This fluid cylinder is provided with a pivotable anchor point 79 (the details of which are not shown) which permits the cylinder 78 to pivot relative to the gripper assembly. The piston rod 81 is connected to lug 67 by pin 82. By reference to the upper portion of FIG. 4, it will be noted that the connection points 79 and 82 and the center of rotation 62 of the rotator are in line when the rotator is in its intermediate or center position. As these points are in line, substantially no force is exerted tending to rotate the rotor in either direction. The rotor will normally be fairly difficult to turn due to packing therein. Such packing will prevent rotation of the rotor from this intermediate position until it is acted upon by one of the trip assembly lugs. If desired, a suitable detent may also be provided in the valve to hold it in this intermediate position.

In the illustrated form of the invention, the three-position valve rotor is prevented from moving from its intermediate position by the planar surface 75 of the trip assembly which lies very close to the rotator lugs which cooperate therewith as the rotator passes by the trip assembly. If there is any tendency for the rotator to move from its intermediate position, the pair of lugs adjacent the trip assembly will engage the surface 75, and the rotator will be prevented from leaving its intermediate position until after the lead rotator lug has passed over the trip assembly.

Referring to FIG. 6 again, it will be noted that the cylinder 78 receives pressure from the low-pressure side of the fluid system. Thus, the accumulator 53 will be constantly urging fluid into the several cylinders 78 and urging the rotator toward either of its extreme positions once the rotator is moved out of the intermediate position.

During certain pipe handling operations, it is desirable that several of the grippers in the lowermost position remain open for a short distance above the lower sprockets to facilitate the handling of the drill pipe. For this purpose, the lower trip assembly 63 is mounted on a member 80 with a suitable slide arrangement indicated generally at 60. As best shown in FIG. 4, the lower trip assembly 63 is supported on a plate 101 which is slidable on the vertical member 80. As shown in FIG. 3, the lower trip assembly is moved vertically by an articulating arm having an inboard portion 102 and outboard portion 83, which is pinned to plate 101. A suitable actuator cylinder is indicated generally at 84. The cylinder is attached to the inboard ann 102 at 85 and extension of the piston rod 86 in the cylinder raises the articulated arm which is pivoted to the frame as indicated generally at 87.

- ln operation of this form of the invention, an open gripper assembly may be considered to be moving upwardly in FIG. 4. As it approaches the lower trip assembly 63, the lug 67 is in engagement with stop 72. The lug 65 will be in approximately a 12 o'clock position, as viewed in FIG. 4, and thus as the assembly moves upward the lug 65 clears the lower trip assembly. However, the lug 67 of the rotator comes in contact with surface 73 of the trip assembly, and continued upward movement of the gripper forces rotation of the rotator to the positions shown in dotted lines adjacent to the lower trip assembly. In this position, the grippers are closing. The valve rotator remains in its intermediate position until this same lug 67 strikes the lug 77 at the upper end of the lower trip assembly starting the valve rotator in its counter clockwise rotation. The rotator is partially rotated by engagement of the lugs, and after a short amount of rotation has taken place the lug is assisted by the resilient force exerted by cylinder 78 to move the rotator to the solid line position of FIG. 4 at which time the gripping assembly is in its grip position.

As the rotator reaches the upper trip assembly, the lug 66 strikes surface 73 on the upper trip assembly and the rotator is moved to the upper dotted line position of FIG. 4. At this time, the valve has been returned to close position. As the rotator leaves the upper trip assembly, the lug 66 strikes lug 77 of the upper trip assembly and begins the rotation of the rotor toward open position. After this rotation is begun, the cylinder 78 and its associated piston urge the rotator toward a full open position until the lug 67 strikes the stop 72.

During reverse travel of the endless chain from that just explained, the other two lugs are cooperative with the trip assemblies to shift the valve rotator. Thus, when the valve rotator is moving downwardly, as viewed in FIG. 4, the lug 68 of the rotator cooperates with surface 74 of the upper trip assembly to move the rotator from open to close position and then to grip position as the lug 68 of the rotator passes over lug 76 on the trip assembly. Then when the rotator reaches the lower trip assembly, the lug 65 engages surface 74 to move the rotator to close position, and then the lug 65 engages lug 76 to move the rotator to open position.

It will be appreciated that the system illustrated in FIG. 4 is one in which close tolerances are not required and flexure of the endless chain will not effect the operation. For this reason, the system shown in FIG. 4 is preferred. However, other systems of lugs could be utilized, such as the rack-and-pinion system shown in FIG. 8. In this instance, the valve rotator is in the form of a pinion 88, and the two trip assemblies are in the form of racks, indicated generally at 89 and 9l. Each rack has a plurality of

teeth

92 and 93 at its extremities and an intermediate section 94 which has no teeth and does not engage the pinion 88.

The rack teeth 93 provide lugs on the lower assembly which rotate the pinion 88 and move the valve operator from open to close position. The pinion remains in the close position as it passes by the toothless section 94 of the rack. At the upper section of the rack, the teeth 92 further rotate the pinion to the grip position. As the pinion reaches the upper trip assembly, the lower teeth 93 return the pinion to close position and the upper teeth 92 rotate the pinion to the open position. Of course, a number of rack teeth could be utilized to fully rotate the pinion, or, as an alternative, the pinion could be started in its rotation by rack teeth and then moved to the full extreme position by a resilient assist such as is provided in the FIG. 4 form of this invention.

From the above, it will be appreciated that the planar surface 75 is optional but is preferred as it will positively prevent the valve rotor from moving out of its intermediate position before the fluid system has had an opportunity to move the grippers to close position. It will be obvious that the several lugs provided on each trip assembly could be provided in any desired manner and take any desired form.

The resilient means 78 is optional, but it is preferred where the valve has a substantial arc of movement such as the approximate illustrated. Where such resilient assist is not used the resistance of the valve to rotation may be depended upon to hold it in its three positions,'or suitable internal detents may be provided in the valve if desired.

The foregoing disclosure and description of the invention are illustrative and explanatory thereof and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made within the scope of the appended claims without departing from the spirit of the invention.

What is claimed is:

1. A retractor comprising:

a support;

an endless chain on the support;

a plurality of grippers carried by the chain;

a fluid system for controlling the grippers including threeposition rotary valves on the endless chain;

said system in said three valve positions exerting close, grip,

and open forces on said grippers;

and means for shifting each valve between said three positions comprising;

a valve rotator,

a plurality of lugs on said rotator,

a first trip assembly on the support having at least one lug for engaging a rotator lug and moving the rotator to closed position and at least another lug spaced from said one lug for engaging a rotator lug and moving the rotator to grip position as the rotator moves past the first trip assembly,

and a second trip assembly on the support having at least one lug for engaging a rotator lug and moving the rotator to said closed position and at least another lug spaced from said one lug of the second trip assembly for engaging a rotator lug and moving the rotator to open position as the rotator moves past the second trip assembly,

said trip assemblies moving said rotator to said close, grip and open positions with the endless chain moving in either direction.

2. The retractor of claim 1 wherein means are provided for holding said valve rotator in said open, close and grip positions until the rotator is engaged and rotated by said trip assembly lugs.

3. The retractor of claim 1 wherein one of said trip assemblies is movable toward and away from the other trip assembly to control the number of rotators which are simultaneously in gripping position.

4. The retractor of claim 1 wherein means are provided for holding said valve rotator in said closed position until the rotator contacts a lug on one of said trip assemblies;

and means for provided for assisting said lugs and moving said rotator to full open and full grip position after initial rotation of said rotator from said closed position and for holding said rotator in full open and full grip position until the rotator contacts a lug on one of said trip assemblies.

5. The retractor of claim 1 wherein means are provided for holding said valve rotator in said closed position until the rotator contacts a lug on one of said trip assemblies;

and resilient means are associated with each three-position valve and connected to each rotator with the anchor point for the resilient means, the connection point of the resilient means to the rotator and the center of rotation of the rotator being substantially in line when the rotator is in closed position and effective to urge the rotator toward grip or open position after the rotator has moved to a position in which said connection and anchor points and center of rotation are no longer in line.

6. The retractor of claim 1 wherein resilient means are associated with each three-position valve and connected to each rotator with the anchor point for the resilient means, the connection point of the resilient means to the rotator and the center of rotation of the rotator being substantially in line when the rotator is in closed position and effective to urge the rotator toward grip or open position after the rotator has moved to a position in which said connection and anchor points and center of rotation are no longer in line.

7. The retractor of claim 1 wherein a fluid system having a high-pressure side and a low-pressure side is connected to said three-position valves and lower pressure fluid from grippers moving toward open position is utilized to move other grippers toward closed position.

8. A retractor comprising;

a support;

an endless chain on the support;

a plurality of grippers carried by the chain;

said system in said three valve positions exerting close, grip and open forces on said gripper;

and means for shifting each valve between such three positions comprising;

a pinion type valve rotator,

a pair of spaced racks cooperative with said rotator,

each rack having teeth at its end for engagement with said rotator and a space between said teeth in which the rotator does not engage the rack,

said racks having their teeth facing in opposite directions and successively engaging said rotator to move at first to closed position, then to grip position, then to close position, and then to open position with the endless chain moving in either direction.

9. The retractor of claim 8 wherein one of said racks is movable toward and away from the other rack to control the number of rotators which are simultaneously in gripping position.

10. A retractor comprising;

a support;

an endless chain on the support;

a plurality of grippers carried by the chain;

said system in said three valve positions exerting close, grip and open forces on said grippers;

and means for shifting each valve between said three positions comprising;

a valve rotator,

a pair of lugs on opposite sides of said rotator lying in a first plane of rotation of said rotator,

a second pair of lugs on opposite sides of said rotator lying in a second plane of rotation of said rotator,

said lugs being spaced from each other circumferentially of the rotator,

a pair of spaced trip assemblies each having a planarsurface substantially perpendicular to said planes of rotation and adjacent one of each pair of lugs when the rotator is in closed position and moving past said surface,

the ends of said planar surface acting as lugs to engage said rotator lugs and move the rotator to closed position,

and a lug at each end of each trip assembly extending toward the rotator from said planar surface with one of the extending lugs lying in said one plane of rotation and the other of the extending lugs lying in said second plane of rotation,

said extending lugs engaging the trailing rotator lug as it reaches the end of said planar surface to move the rotator to either grip or open position.

11. The retractor of claim 10 wherein the fluid system has a high-pressure side and a low-pressure side connected to said three-position valves and low-pressure fluid from grippers moving toward open position is utilized to move other grippers toward closed position.

12. The retractor of claim 10 wherein means are provided for holding said valve rotator in said open, close, and grip positions until the rotator is engaged and rotated by said trip assembly lugs.

13. The retractor of claim 10 wherein one of said trip assemblies is movable toward and away from the other trip assembly to control the number of rotators which are simultaneously in grip position.

14. The retractor of claim 10 wherein resilient means are associated with each three-position valve and connected to each rotator with the anchor point for the resilient means, the connection point of the resilient means to the rotator and the center of rotation of the rotator being substantially in line when the rotator is in closed position and effective to urge the rotator toward grip or open position after the rotator has moved to a position in which said connection and anchor points and center of rotation are no longer in line.

15. A retractor comprising;

a support;

an endless chain on the support;

a plurality of grippers carried by the chain;

and means for shifting each valve between said three posi' tionsicomprising;

a valve rotator,

a plurality of lugs on said rotator,

a first trip assembly having a first lug for engaging a rotator lug to move the rotator to close position and a second lug engaging a rotator lug to move the rotator to grip position,

and a second trip assembly having lug means for engaging a rotator lug to move the rotator to open position.

16. The retractor of claim 15 wherein the fluid has a highpressure side and a low-pressure side connected to said threeposition valves and low-pressure fluid from grippers moving toward open position is utilized to move other grippers toward closed position.

17. The retractor of claim 15 wherein means are provided for holding said valve rotator in said open, close and grip position until the rotator is engaged and rotated'by said trip assembly lugs.

18. The retractor of claim 15 wherein one of said trip assemblies is movable toward and away from the other trip as sembly to control the number of rotators which are simultaneously in grip position.

19. The retractor of claim wherein a means are provided for holding said valve rotator in said closed position until the rotator contacts a lug on one of said trip assemblies and means are provided for assisting said lugs in moving said rotator to full open and full grip position after initial rotation of said rotator from said closed position and for holding said rotator in full open and full grip position until the rotator contacts a lug on one of said trip assemblies.

20. The retractor of claim 15 wherein a means are provided for holding said valve rotator in said closed position until the rotator contacts a lug on one of said trip assemblies;

and resilient means associated with each three-position valve and connected to each rotator with the anchor point for the resilient means, the connection point of the resilient means to the rotator and the center of rotation of the rotator being substantially in line when the rotator is in closed position and effective to urge the rotator toward grip or open position after the rotator has moved to a position in which said connection and anchor points and center of rotation are no longer in line.

21. The retractor of claim 15 wherein resilient means are associated with each three-position valve and connected to each rotator with the anchor point for the resilient means, the connection point of the resilient means to the rotator and the center of rotation of the rotator being substantially in line when the rotator is in closed position and effective to urge the rotator to grip or open position after the rotator has moved to a position in which said connection and anchor points and center of rotation are no longer in line.

Claims

1. A retractor comprising: a support; an endless chain on the support; a plurality of grippers carried by the chain; a fluid system for controlling the grippers including threeposition rotary valves on the endless chain; said system in said three valve positions exerting close, grip, and open forces on said grippers; and means for shifting each valve between said three positions comprising; a valve rotator, a plurality of lugs on said rotator, a first trip assembly on the support having at least one lug for engaging a rotator lug and moving the rotator to closed position and at least another lug spaced from said one lug for engaging a rotator lug and moving the rotator to grip position as the rotator moves past the first trip assembly, and a second trip assembly on the support having at least one lug for engaging a rotator lug and moving the rotator to said closed position and at least another lug spaced from said one lug of the second trip assembly for engaging a rotator lug and moving the rotator to open position as the rotator moves past the second trip assembly, said trip assemblies moving said rotator to said close, grip and open positions with the endless chain moving in either direction.

4. The retractor of claim 1 wherein means are provided for holding said valve rotator in said closed position until the rotator contacts a lug on one of said trip assemblies; and means for provided for assisting said lugs and moving said rotator to full open and full grip position after initial rotation of said rotator from said closed position and for holding said rotator in full open and full grip position until the rotator contacts a lug on one of said trip assemblies.

5. The retractor of claim 1 wherein means are provided for holding said valve rotator in said closed position until the rotator contacts a lug on one of said trip assemblies; and resilient means are associated with each three-position valve and connected to each rotator with the anchor point for the resilient means, the connection point of the resilient means to the rotator and the center of rotation of the rotator being substantially in line when the rotator is in closed position and effective to urge the rotator toward grip or open position after the rotator has moved to a position in which said connection and anchor points and center of rotation are no longer in line.

8. A retractor comprising; a support; an endless chain on the support; a plurality of grippers carried by the chain; a fluid system for controlling the grippers including three-position rotary valves on the endless chain; said system in said three valve positions exerting close, grip and open forces on said gripper; and means for shifting each valve between such three positions comprising; a pinion type valve rotator, a pair of spaced racks cooperative with said rotator, each rack having teeth at its end for engagement with said rotator and a space between said teeth in which the rotator does not engage the rack, said racks having their teeth facing in opposite directions and successively engaging said rotator to move at first to closed position, then to grip position, then to close position, and then to open position with the endless chain moving in either direction.

10. A retractor comprising; a support; an endless chain on the support; a plurality of grippers carried by the chain; a fluid system for controlling the grippers including three-position rotary valves on the endless chain; said system in said three valve positions exerting close, grip and open forces on said grippers; and means for shifting each valve between said three positions comprising; a valve rotator, a pair of lugs on opposite sides of said rotator lying in a first plane of rotation of said rotator, a second pair of lugs on opposite sides of said rotator lying in a second plane of rotation of said rotator, said lugs being spaced from each other circumferentially of the rotator, a pair of spaced trip assemblies each having a planar surface substantially perpendicular to said planes of rotation and adjacent one of each pair of lugs when the rotator is in closed position and moving past said surface, the ends of said planar surface acting as lugs to engage said rotator lugs and move the rotator to closed position, and a lug at each end of each trip assembly extending toward the rotator from said planar surface with one of the extending lugs lying in said one plane of rotation and the other of the extending lugs lying in said second plane of rotation, said extending lugs engaging the trailing rotator lug as it reaches the end of said planar surface to move the rotator to either grip or open position.

15. A retractor comprising; a support; an endless chain on the support; a plurality of grippers carried by the chain; a fluid system for controlling the grippers including three-position rotary valves on the endless chain; said system in said three valve positions exerting close, grip and open forces on said grippers; and means for shifting each valve between said three positions comprising; a valve rotator, a plurality of lugs on said rotator, a first trip assembly having a first lug for engaging a rotator lug to move the rotator to close position and a second lug engaging a rotator lug to move the rotator to grip position, and a second trip assembly having lug means for engaging a rotator lug to move the rotator to open position.

16. The retractor of claim 15 wherein the fluid has a high-pressure side and a low-pressure side connected to said three-position valves and low-pressure fluid from grippers moving toward open position is utilized to move other grippers toward closed position.

17. The retractor of claim 15 wherein means are provided for holding said valve rotator in said open, close and grip position until the rotator is engaged and rotated by said trip assembly lugs.

18. The retractor of claim 15 wherein one of said trip assemblies is movable toward and away from the other trip assembly to control the number of rotators which are simultaneously in grip position.

19. The retractor of claim 15 wherein a means are provided for holding said valve rotator in said closed position until the rotator contacts a lug on one of said trip assemblies and means are provided for assisting said lugs in moving said rotator to full open and full grip position after initial rotation of said rotator from said closed position and for holding said rotator in full open and full grip position until the rotator contacts a lug on one of said trip assemblies.

20. The retractor of claim 15 wherein a means are provided for holding said valve rotator in said closed position until the rotator contacts a lug on one of said trip assemblies; and resilient means associated with each three-position valve and connected to each rotator with the anchor point for the resilient means, the connection point of the resilient means to the rotator and the center of rotation of the rotator being substantially in line when the rotator is in closed position and effective to urge the rotator toward grip or open position after the rotator has moved to a position in which said connection and anchor points and center of rotation are no longer in line.