Casing hanger assembly and operating tools therefor

Abstract

A casing hanger assembly adapted to be set in a wellhead by longitudinal actuation, and operating tools for running, setting and retrieval thereof. A circulating casing hanger having a body including a fluid passageway carrying a seal sleeve having a seal for sealing in the passageway. A longitudinally movable actuator for moving a locking ring and the sleeve downwardly to set the seal and engage the ring in a locking recess in the body. Coacting tapering faces directed inwardly and downwardly between the locking ring and the recess and coacting tapering faces directed downwardly and outwardly between the actuator and locking ring providing a releasable holding structure as well as providing a mechanical advantage for setting the seal. Various locking means and energy storage means may be used to maintain the seal in a set position. Hanger and protector bowl setting and retrieving tools for operating the assembly.

Parent Case Text

This is a division of application Ser. No. 357,832, filed May 7, 1973, now U.S. Pat. No. 3,827,488.

Description

BACKGROUND OF THE INVENTION

Generally, the use of circulating casing hanger assemblies for landing in a wellhead mandrel and permanently cementing well hole casing is old as shown in U.S. Pat. No. 3,460,615.

The present invention is directed to various improvements in a casing hanger assembly which may be run into a wellhead mandrel, the seal set and tested. Emergency retrieval of the seal assembly may be performed in the event the seal is unsatisfactory. The bowl protector may be run and retrieved in combination with the casing hanger or independently therefrom. And improved operating tools for running, setting, testing and retrieving various components of the circulating casing hanger assembly are provided.

SUMMARY

The present invention is directed to a casing hanger assembly in which the hanger seal may be set by longitudinal movement into a releasable locking engagement, and may be released by longitudinal actuation. The casing hanger body includes a fluid passageway with a longitudinally movable seal sleeve having a seal for closing the passageway, and a longitudinally movable actuator for moving the sleeve and seal into a sealing relationship in the passageway. The body includes a locking recess for receiving a locking ring which is moved by the actuator for releasably holding the seal in a sealed position. Tapering coacting faces are provided between the actuator and the locking ring and between the locking ring and the locking recess to provide a wedging action for setting the seal which provides a releasable locking function as well as providing a mechanical advantage in setting the seal. Additional releasable locking means may be provided between the actuator and the sleeve holding the seal in an expanded position such as releasable coacting ratchet teeth which may be released by a retrieving tool. Furthermore, energy storage means may be provided for maintaining a setting force on the set seal. This is also releasable.

Another object of the present invention is the provision of a hydraulic setting tool for moving the actuator and setting the seal by providing a piston and cylinder assembly connected to a running string and adapted to be positioned in engagement with the actuator wherein fluid pressure applied to the running string may actuate the piston and cylinder assembly and set the casing hanger seal.

Still a further object of the present invention is the provision of a longitudinally movable weight setting tool for longitudinally moving the actuator and setting the seal of the casing hanger.

Still a further object of the present invention is the provision of a retrieving tool for emergency retrieval of the seal assembly in the event the seal is unsatisfactory which includes an engaging surface for releasing the releasable locking means holding the seal in engagement, and includes retrieving lugs for engaging the actuator and retrieving the actuator, the sleeve and the locking ring.

Yet a still further object is the provision of a bowl protector setting and retrieving tool for running and setting the bowl protector in combination with a casing hanger.

Still a further object of the present invention is the provision of a running and retrieving bowl protector tool for setting or retrieving a bowl protector independently of the casing hanger in which the protector includes a tool engaging opening one side of which includes a tapered face, and the bowl running tool includes a spring-loaded lug for engaging the protector opening with a lug-locking sleeve carried by the running tool which is yieldably urged toward the lug and engages a locking notch in the lug after the protector is set and the tool is rotated against the opening tapered face moving the lug to a locking position. The tool may also be used to retrieve the bowl protector by locking the locking sleeve in a disengaged position whereby the lugs may engage the bowl protector opening and retrieve the bowl protector.

Yet a further object is the provision of a running and/or retrieving tool having spring actuated dogs for engaging, setting, or retrieving a bowl protector or casing hanger seal assembly by longitudinal movement without requiring any rotational orientation or rotational actuation. The spring actuated dogs may be released downhole by actuation of a hydraulic release for setting of equipment all without requiring rotative movement of the tool.

Other and further objects, features and advantages will be apparent from the following description of presently preferred embodiments of the invention, given for the purpose of disclosure and taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary elevational view, in cross-section, illustrating the casing hanger assembly of the present invention placed in position in a wellhead mandrel prior to cementing the casing,

FIG. 2 is a fragmentary elevational view, in cross-section, with the running tool positioned in washing position for cleaning the seal and seating area,

FIG. 3 is a fragmentary elevational view, in cross-section, showing a hydraulic setting tool in position for setting the casing hanger seal,

FIG. 4 is a fragmentary elevational view, in cross-section, illustrating a mechanical weight setting tool in position for setting the casing hanger seal,

FIG. 5 is a fragmentary elevational view, partly in cross-section, of the casing hanger assembly in a wellhead mandrel after the seal is set,

FIG. 6 is an enlarged cross-sectional view taken along the line 6--6 of FIG. 5,

FIG. 7 is an enlarged cross-sectional view taken along the line 7--7 of FIG. 5,

FIG. 8 is a fragmentary elevational view, partly in cross-section, illustrating a retrieving tool for retrieving the seal assembly of the casing hanger,

FIG. 9 is a fragmentary elevational view, in cross-section, of a bowl protector running tool shown in position for running a bowl protector independently of the casing hanger,

FIG. 10 is a cross-sectional view taken along the line 10--10 of FIG. 9 showing the running tool of FIG. 9 adapted to retrieve a bowl protector independently from the casing hanger

FIG. 11 is a fragmentary elevational view, in cross-section, of another embodiment of a setting and retrieving tool shown in an enlarged position,

FIG. 12 is a cross-sectional view taken along the line 12--12 of FIG. 11,

FIG. 13A is a fragmentary elevational view, in cross-section of the tool of FIGS. 11 and 12, showing the setting tool in a released position after setting a bowl protector,

FIG. 13B is a fragmentary elevational view, showing the setting tool of FIGS. 11 and 12, in position retrieving a casing hanger seal,

FIG. 14 is a fragmentary elevational view, in cross-section, showing another embodiment of a casing hanger seal assembly shown in an unset position, and

FIG. 15 is a fragmentary elevational view, in cross-section, of the seal assembly of FIG. 14 shown in the set position.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings and particularly to FIG. 1, the reference numeral 10 generally indicates the casing hanger assembly of the present invention attached to a running tool 12 for seating in a wellhead mandrel 14 for supporting well hole casing 16 within a well for conventionally cementing the well hole casing 16 into the well.

The casing hanger assembly 10 includes a casing hanger generally indicated by the numeral 17 and includes a casing hanger body 18 having a landing shoulder 20 for landing on a shoulder 22 in the wellhead mandrel 14 for supporting the assembly 10 therefrom. The body 18 also includes internal threads 24 for connection to the well hole casing 16 for supporting the casing 16 therefrom. The body 18 further includes internal threads 26, preferably left-handed threads, for supporting the assembly 10 from a running tool 12 for insertion into the mandrel 14. The body 18 further includes wash ports 28 whose purpose and function will be more fully described hereinafter. In addition, an internal cement return passageway is provided in or about the body 18 for the return of cement flowing up about the outside of the well hole casing 16 through ports 30 and 32 (FIGS. 1 and 5) into the annulus 29 within the wellhead casing above the assembly 10. A snap ring 21 is provided on the body 18 for engagement with a wellhead mandrel groove 23 for releasably holding the assembly in the mandrel 14. A locking recess 34 is provided in the body 18 whose function and purpose will be more fully described hereinafter.

The assembly 10 also includes the seal assembly including a sleeve 36 having a seal 38 for sealing the passageway between the body 18 and the wellhead mandrel 14, a locking ring 40 positioned between the body 18 and the sleeve 36 and an actuator 42 which when moved longitudinally downwardly moves the sleeve 36 and locking ring 40 downwardly and moves the seal 38 into sealing engagement between the body 18 and the mandrel 14. Initially, the seal assembly, consisting of the sleeve 36, the locking ring 40 and the actuator 42, are retained in an upward position, such as by a shear pin 44, for holding the seal 38 out of the passageway including the ports 30 and 32 for conducting conventional cementing operations. The assembly 10 also includes a bowl protector 46 which may be run with the casing hanger 17 or independently therefrom.

The casing hanger assembly 10 is initially run with a running tool 12 generally consisting of a section of pipe of the same inside diameter as the casing 16. The tool 12 is screwed into the body 18, preferably with a coarse left-handed thread 48 coacting with the thread 26 on the body 18 and made up with two O-ring seals 50 coacting with the body 18 to initially close the wash ports 28. The assembly 10 is lowered into the well until the shoulder 20 on the body 18 is seated on a landing shoulder 22 of the wellhead mandrel 14. The snap ring 21 snaps into place in the groove 23 releasably holding the body 18 in the mandrel 14, all as best seen in FIG. 1. Conventional cementation is started and completed for cementing the casing 16 in the well bore by pumping cement down the interior bore of the tool 12 and casing 16 and upwardly about the outside of the casing 16, through the passage 29 including ports 30 and 32.

As previously mentioned, the bowl protector 46 may be run in combination with the casing hanger 17. An adapter 52 may be threadably secured to the upper end of the sleeve 36 for slidably engaging and holding the lower end of the bowl protector 46. The bowl protector 46 may include a split ring 54 for coacting with a groove 56 in the mandrel 14. Preferably, the groove 56 includes a pin 58. A shear pin 60 is provided between the running tool 12 and the bowl protector 46 for rotating the bowl protector 46 and the ring 54 until the gap in the split ring 54 mates with the pin 58 allowing the snap ring 54 to snap into the groove 56 for preventing rotation of the protector bowl 46.

After the cementing operations are completed, the seal 38 and its seating area are cleaned prior to setting the seal 38. Referring now to FIG. 2, the running tool 12 is rotated to the right unscrewing the left-handed connection between the threads 48 and 26 to back off the lower seal 50 on the running tool 12 to open the wash ports 28. Water is now circulated down through the bore of the tool 12, through the wash ports 28 and up through the annulus 29 between the running tool and the wellhead mandrel 14 to clean the seating areas and the seal 38. Rotation of the running tool 12 will also shear pin 60 between the running tool 12 and the bowl protector 46. After the washing is completed, further rotation of the running tool 12 will uncouple the running tool from the body 18 and the running tool 12 is pulled from the well.

Referring now to FIGS. 3 and 4, two types of tools for setting and testing the seal 38 are shown. Referring to FIG. 3, a hydraulic setting and testing tool 62 is shown connected to the running string 64 and provided with a shoulder 66 which may be engaged by a blowout preventer ram 68 for preventing upward movement of the tool 62 and string 64 when actuating the seal 38. The hydraulic tool 62 includes a cylinder and piston assembly having a cylinder 70 and piston 72 with a port 74 communicating with the bore of the tool 62 and running string 64. The piston 72 is adapted to be positioned and engage the actuator 42 longitudinally moving the actuator 42 in a downward direction. Referring to FIG. 2, the seal sleeve 36 includes an upwardly directed shoulder 80 for intially carrying the locking ring 40 at a position above the locking recess 34. It is also noted that the actuator 42 is positioned above and contacts the top of the locking ring 40 so that on downward movement of the actuator 42, the retaining shear pin 44 is sheared and the actuator 42 drives the locking ring 40 and the seal sleeve 36 downwardly carrying the seal 38 downwardly. The actuator 42 includes a tapered face 82 which is adapted to coact with a tapered face 84 on the locking ring 40 when the ring 40 snaps into position in the locking recess 34 in the body 18. The top of the locking recess 34 includes a tapered face 86 which coacts with a tapered face 88 on the top of the locking ring 40.

Referring now to FIG. 3, a ball 94 is provided to drop downhole and seat on seat 96 and when hydraulic pressure is applied to the bore of the tool 62, through port 74, the piston 72 is moved downwardly moving the actuator 42 downwardly shearing pin 44 and moving the locking ring 40 into the locking recess 34 which carries sleeve 36 and seal 38 longitudinally downwardly. Further longitudinal thrust on the actuator 42 wedges the shoulder 88 on the locking ring 40 against the shoulder 86 at the top of the locking recess 34 causing further compression of the seal 38 as its lower end contacts a shoulder 90 on the body 18 and expands between the mandrel 14 and the body 18. The desired compression of the seal 18 may be obtained through the combination of a self-locking taper between the coacting outwardly and downwardly directed faces 82 on the actuator 42 and 84 on the locking ring 40 such as a 7.degree. self-locking taper, and against the taper between the inwardly and downwardly directed coacting faces 86 and 88 which may be a 45 degree taper. The two pair of coacting tapering faces, in addition to providing a releasable locking mechanism for the seal 38, also provide a 3 or 4-to-1 mechanical advantage reducing proportionately the required setting pressure of the piston 72. Thus, as shown in FIG. 3, the seal 38 is in a set position.

However, an additional locking system to the self-locking taper between the tapering faces 82 and 84 of the actuator 42 and locking ring 40 is provided since vibration may loosen the locking taper and release the seal 38. Additional releasing locking means may be provided, as best seen in FIGS. 5-7 in which upwardly directed ratchet teeth 100 are provided on the actuator 42 to coact with ratchet teeth segments 102 having downwardly directed teeth 104. The ratchet segments 102 are carried by the seal sleeve 36 in a recess 106 and are yieldably urged inwardly into contact with the actuator 42 by suitable spring means such as rubber pads 108. As the actuator 42 is moved downwardly, the coacting ratchet teeth 100 and 104 will ratchet under the action of the resilient pads 107 to allow the actuator 42 to move downwardly relative to the sleeve 36 to lock the seal 38 in a compressed position and prevent relaxation of the seal 38. However, in the event it is desired to remove the seal assembly, as will be discussed hereinafter, the coacting ratchet teeth 100 and 102 must be separated and segment-releasing elements 110 are provided carried by the actuator 42 and positioned against the ratchet segment 102 and having ends 112 which protrude inwardly from the actuator 42 for contact by suitable means. Thus, when the ends 112 are pressed outwardly, the segment 102 will move against the resilient pads 108 disengaging the ratchet teeth 100 and 102 allowing the actuator 42 to be moved upwardly relative to the sleeve 36.

After the seal 38 is set, it is tested to ascertain whether it is sealing properly. The setting and testing tool 62 (FIG. 3) includes a testing seal 92 for sealing against the body 18. Pressure may be applied downwardly onto seal 38 through the annulus 29, ports 98 in piston 72 of tool 62, and ports 32. In the event that the testing seal 92 leaks, bursting of the casing 16 is avoided since excess pressure in the casing 16 may push the ball 94 off of its seat and be released through the bore 31.

In the event that the test shows that the seal 38 is not suitably holding or if for any other reason it is desired to remove the seal assembly, a retrieving tool 114, as best seen in FIG. 8, is provided. The retrieving tool 114 includes a plurality of spline grooves 116 and upsets 118 to coact with the corresponding upsets 120 and grooves 122 of the actuator 42, as best seen in FIG. 5. In inserting the retrieving tool 114 into the actuator 42, should the upsets 118 contact an upset 120 on the actuator 42, slight rotation will cause the spline-like assemblies to coact. In addition, it is noted that the upsets 118 on the retrieving tool 114 will engage the inner ends 112 of elements 110 to move the teeth segments 102 away from the actuator 42 and release the releasable locking ratchet teeth 100 and 102 to allow the actuator 42 to be moved upwardly and retract from the locking ring and sleeve 36. In addition, the retrieving tool 114 includes a plurality of spring-loaded lugs 124 that move downwardly over the upsets 120 on the actuator 42 and engage an engaging shoulder 126. Upward pull on the retrieving tool 114 longitudinally moves the actuator 42 upwardly releasing the locking ring 40. Further upward movement of the actuator 42 causes the top 128 of the actuator to engage the bottom of the adapter 52 thereby raising the sleeve 36 and locking ring 40 along with the actuator 42. Upward movement will cause the sleeve 36 to come in contact with the bottom of the protector bowl 46 to retrieve the protector bowl 46 along with the seal assembly from the well.

After the seal assembly has been removed and checked, it may be rerun and set with the setting and testing tool 62 shown in FIG. 4 by supporting the seal assembly from the tool 62 with a shear pin 132, so that the sleeve 36, actuator 42 and locking ring may be reinserted around the body 18 of the casing hanger. The hydraulic setting tool 62 may be modified, as best seen in FIG. 4, to provide a hydraulic weight-setting tool by inserting a spacer bar 134 in the piston and cylinder assembly or by merely setting down on the tool 62 until the cylinder 70 closes on the piston 72. Mechanically and longitudinally moving the tool 62 downwardly around the body 18 will longitudinally set or reset the seal 38 as in the operation described in connection with FIG. 3.

As has been previously described, in connection with FIG. 1, the protector bowl 46 may be run in combination with the casing hanger 17. In addition, the protector bowl 46 may also be run and retrieved separately from the casing hanger 17. Referring to FIG. 9, the bowl protector 46 includes a tool engaging opening 140 which includes, as best seen in FIG. 1, a tapered face 142 tapering inwardly on one side. A protector bowl tool 144 is provided for connection to a running string (now shown) and having spring-loaded lugs 146 adapted to engage the openings 140 in the bowl protector 46. The tool 144 also includes a lug locking sleeve 148 which is actuated by a spring 150 toward the lug 146. The lug 146 includes a locking notch 152 on its inwardly end whereby when the lug 146 is pressed inwardly the notch 152 will be engaged by the lower end 154 of the locking sleeve 148. To independently set the bowl protector 46 the tool 144 is assembled at the well surface with the spring-loaded lugs 146 positioned in the openings 140 of the bowl protector 46 supporting the bowl protector from the tool 144. The tool 144 and bowl protector 46 are lowered into the wellhead mandrel 14 until the split ring 54 snaps into the coacting groove 56 in the well mandrel. The tool 144 is then rotated to the right and the lugs 146 will be compressed inwardly by the taper 142 (FIG. 1) bringing the locking notch 152 into alignment with the lower end 154 of the locking sleeve 148 thereby locking the lugs 146 in an inwardly or depressed position. The tool 144 may then be retrieved upwardly from the wellhead mandrel 14.

The tool 144 may also be used to retrieve the bowl protector 46 independently from the casing hanger 17. For retrieval operations, the locking sleeve 148 must be neutralized in order to allow the spring-loaded lugs 146 to move inwardly as the tool 146 is moved down the well and to spring outwardly into the openings 140 of the bowl protector 46. As best seen in FIG. 10 a screw 156 is inserted in the tool 144 engaging the bottom end 154 of the locking sleeve 148 and holding the sleeve 148 in the upward position and away from the locking notch 152 of the lugs 146 (FIG. 9). The tool 144 is then run down until the shoulder 160 on the tool 144 contacts the shoulder 162 on the bowl protector 46 thereby aligning and inserting the lugs 146 in the openings 140. A straight upward pulling action on the tool 144 will retrieve the bowl protector 46 from the mandrel 14.

Of course, other and further modifications of the present invention may be utilized. Referring now to FIGS. 11, 12 and 13, a modified setting and retrieving tool which is spring actuated and hydraulically released is best seen for running and retrieving a bowl protector and for retrieving a casing hanger seal assembly. The tool generally indicated by the reference numeral 170 includes a body 172 adapted to be attached to an operating string (not shown), a hydraulic piston 174, and locking dogs 176. Springs 178 are provided between the hydraulic piston 174 and the dogs 176 yieldably urging the dogs 176 outwardly. As best seen in FIG. 11, the tool 170 may act as a retrieving tool to retrieve any objects such as a bowl protector 180 having an annular engaging notch 182. In this event, the tool 170 may be moved downhole and the dogs 176 will bypass any obstructions or shoulders in the hole by moving inwardly against the spring 178. When the dogs 176 are positioned in the notch 182, an upward pull may be taken by the tool 170 for retrieving the bowl protector 180. It is noted that no rotative orientation or turning of the tool 170 is required for engagement with the notch 182 and that the tool 170 has the advantage of retrieving solely with longitudinal movement.

In addition, as best seen in dotted outline in the lower portion of FIG. 13B, a tool 170a may be provided similar to tool 170 but of a smaller o.d., to engage and retrieve the hanger seal assembly since the dogs 176a will engage the actuating shoulder 126 for moving the actuator 42 upwardly for removing the seal assembly as previously described, and with only longitudinal movement. The tool 170 and 170a is operable without requiring the rotational alignment as required with the tool described in connection with FIG. 8.

The tool 170, in addition to retrieving equipment in the well by mere longitudinal movement, can also run and set equipment therein solely by longitudinal movement. The piston 174 includes a first enlarged diameter section 184 which normally abuts one end of the spring 178. The piston 174 also includes a second smaller diameter section 186. The piston 174 also includes a groove 188 for engagement by a spring loaded plunger 190 for normally holding the piston 174 with the diameter section 184 in registry with the end of the spring 178. Hydraulic fluid may be pumped into the bore 192 of the tool 170 forcing the piston 174 downwardly, as best seen in FIG. 13A, against a retaining ring 194 and bringing a second groove 196 into engagement with the spring actuated plunger 190 for holding the piston 174 in a lower position. The downward movement of the piston 174 moves the larger diameter section 184 out of engagement with the spring 178 and moves the smaller diameter section 186 into engagement with the spring 178. Of course, the movement of the smaller diameter section 186 downwardly into alignment with the spring 178 reduces the outward force of the spring 178 against the locking dogs 176. As best seen in FIG. 12, the dogs 176 are movably secured to the body 172 by pins 192 and 194 and springs 196 and 198 which yieldably urge the dogs 176 inwardly toward the body 172. When the piston 174 is in the upward position, as shown in FIG. 11, the spring 178 is in a more compressed state and overcomes the springs 196 and 198 and urges the locking dogs 176 outwardly into an engaging position. However, when the piston 174 is moved to a downward position, as best seen in FIG. 13, with the spring 178 abutting the smaller diameter section 186, the springs 196 and 198 overcome the spring 178 and move the locking dogs 176 inwardly into a released position. Again, it is noted that the tool 170 may set and release equipment solely by longitudinal movement and without requiring rotational orientation or rotational actuation.

Referring now to FIGS. 14 and 15, a further embodiment of the casing hanger seal assembly is best shown wherein like parts to those in FIGS. 1-8 are shown with like numbers and the addition of the suffix a. The seal assembly 200 of FIGS. 14 and 15 includes energy storage means such as one or more belleville springs 202 to maintain a compressive force on the actuator 42a and thus on the seal 38a when set to prevent relaxation and possible leak of the seal 38a. That is, the springs 202 are compressed when the seal assembly is set and the springs 202 maintain a continuous pressure on the actuator 42a. As seen, the springs 202 are positioned above and against the actuator 42a and a retaining member 204 is positioned above the springs 202. The setting tool 62 carries the assembly 200 by the shear pin 132a for movement down the well bore and into the mandrel 14. When the setting tool 62 is actuated, such as by the piston 72, the retainer 204 is moved downwardly against the springs 202 which in turn moves the actuator 42a downwardly and as in the previously embodiment, moves the locking ring 40a and sleeve 36a downwardly setting the seal 38a.

Any suitable locking system, such as shown in the embodiment of FIGS. 1-8 may be used, although a simplified means would be a plurality of collet hooks 206 connected to the retainer 204 which engage a downwardly directed hook 208 on the sleeve 36a for holding the compressed belleville spring 202, as best seen in FIG. 15, against the upper end of the actuator 42a thereby maintaining the locking tapers between the members 42a, 40a and seal 38a.

The assembly 200 is retrievable without requiring rotation or orientation by use of the tool 170 described in FIGS. 11-13 by merely shearing the pins 205 that hold the collet hooks 206 to the retainer 204.

The present invention, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned as well as others inherent therein. While presently preferred embodiments of the invention have been given for the purpose of disclosure, numerous changes in the details of construction and arrangement of parts, may be provided, without departing from the spirit of the invention and the scope of the appended claims.

Claims

What is claimed is:

1. A well running and retrieving tool comprising,

a body;

a fluid piston slideably positioned in the body for longitudinal movement therein,

outwardly extending locking dogs having an upwardly directed engaging shoulder carried by the body,

spring means positioned between the piston and the dogs urging the dogs outwardly when the piston is in a first longitudinal position, but releasing the dogs when the piston is moved to a second longitudinal position by fluid pressure away from said spring means thereby releasing the spring means, and

means engaging the dogs yieldably urging the dogs inwardly.

2. A well running and retrieving tool comprising,

a fluid piston slideably positioned in the body for longitudinal movement therein, said piston including first and second portions of different diameters,

outwardly extending locking dogs having an upwardly directed engaging shoulder carried by the body,

first spring means positioned between the piston and the dogs urging the dogs outwardly, said spring initially engaging the portion of the piston having the larger diameter for urging the dogs outwardly for engagement, but engaging the portion of the piston having the smaller diameter when the piston is longitudinally moved by fluid pressure thereby decreasing the outwardly urging force on the dogs by the first spring, and

second spring means engaging the dogs yieldably urging the dogs inwardly.