US2856007A

US2856007A - Well tool anchor

Info

Publication number: US2856007A
Application number: US388138A
Authority: US
Inventors: John V Fredd
Original assignee: Otis Engineering Corp
Current assignee: Otis Engineering Corp
Priority date: 1953-10-26
Filing date: 1953-10-26
Publication date: 1958-10-14
Anticipated expiration: 1975-10-14

Description

Oct. 14, 1958 J. v. FRE'D-D' 2,855,007

' WELL 'rooL ANCHOR Filed Oct. 26, 1955 v 3 Sheets-Sheet s John 1/. Freda g I F ATTORNEY INVENTOR [fl t 2,856,007

Patented Oct. 14, 1958 WELL TOOL ANCHOR John V. Fredd, Dallas, Tex., assignor to Otis Engineering Corporation, Dallas, Tex., a corporation of Texas Application October 26, 1953, Serial No. 388,138

12 Claims. (Cl. 166-214) This invention relates to well tools and more particularly to an anchoring means for locking a well tool in a well against longitudinal displacement in either direction in the well.

One object of the invention is to provide a new and improved anchoring means for well tools.

Another object is to provide an anchoring means, of the type described, which permits the well tool to be lowered into the well tubing by means of a flexible line and locked at a desired position in the well tubing. I

Still another object is to provide an anchoring means, of the type described, which permits removal of the well tool from the well tubing after it has fulfilled its function.

A further object of the invention is to provide an anchoring means for a well tool having lock dogs which are positively held in retracted position while the well tool is being lowered through the tubing and are freed for outward movement into expanded positions to enter into an internal recess of the well tubing to anchor or lock the well tool in the well tubing by means released upon upward movement of the well tool after it has been lowered to the desired position.

A still further object is to provide an anchoring means, of the type described, having means for positively holding said locking means in expanded locking position against movement in either longitudinal direction in the well tubing.

Additional objects and advantages of the invention will be readily apparent from the reading of the following description of a device constructed in accordance with the invention and reference to the accompanying drawings thereof, wherein:

Figure 1 is a view, partly in elevation and partly in section, of the upper portion of the anchoring means showing the various elements of the anchoring means as they appear during downward movement of the well tool through the tubing of a well;

Figure 2 is a continuation of Figure 1 showing the lower portion of the anchoring means;

Figure 3 is an enlarged view, partly in elevation and partly in section, of the upper portion of the anchoring means showing the manner in which the release dogs of the release means engage in an internal recess of the well tubing to release the locking means for movement to expanded position;

Figure 4 is a vertical partly sectional view showing the manner in which the lock dogs are positively held in retracted positions;

Figure 5 is a similar view showing the manner in which the lock dogs are positively held in expanded positions;

Figure 6 is a view, partly in elevation and partly in section, showing the lock dogs in the intermediate position which they assume during upward movement of the anchoring means after the locking means has been released to allow removal of the anchoring means for the well tubing;

Figure 7 is a sectional view taken on the line 7--7 of Figure 1;

Figure 8 is a sectional view taken on the line 8-8 of Figure 5;

Figure 9 is an enlarged exploded view of the plunger, lock dogs, positioning ring and lower end of the top sub of the Well tool; and

Figure 10 is an enlarged isometric view of the tubular body 17 of the well tool.

In the drawings, the numeral 10 designates a well tool anchoring means which includes a top sub 11 having a peripheral groove 12 which is adapted to receive shear pins 13 which releasably secure the top sub to the skirt 14 of a suitable running tool connected to a suitable flexible line running mechanism. The lower portion of the bore -of the top sub is enlarged and threaded, as at 15, and

receives the threaded reduced upper end 16 of a tubular body 17.

A plunger 18 extends slidably through the top sub and the body 17 and is provided with an enlarged H-shaped lower locking portion 153 which has its web cut away at its lower end to provide a pair of dependent spaced legs 20. A pair of

release dogs

21 and 22 disposed between the dependent legs are pivotally connected thereto by a pin 23 which extends through registering apertures in the released dogs and the dependent legs. The release dogs extend outwardly through opposed lateral apertures 23a of the body 17.

A flow sub 26, having an internal. annular seat or shoulder 25 in its bore, is threaded in the lower end of the body 17, and a spring 24 is supported at its lower end on the shoulder 25 and at its upper end is received in a cap 27. The cap 27 includes an annulus 28 and a transverse ridge member 29 which is slidable upwardly between the legs 20, and engages the lower beveled ends 30 of the release dogs, whereby the upward force exerted by the spring 24 acts to rotate or swing the upper ends of the release dogs outwardly through the lateral openings 23a in the tubular body 17 and to urge the plunger rod 18 upwardly.

The upper outer ends of the release dogs have curved surfaces 32 which engage the inner surface of a well tubing 33 which includes tubing sections 34 connected by couplings 35. The engagement of the curved surfaces 32 with obstructions in the well tubing cams the release dogs inwardly toward retracted positions against the resistance of the spring 24 during downward movement of the anchoring means through the tubing.

The upper end portion 37 of the body 17 is provided with notches 36 in which are movably disposed lock dogs 38. The upper portions 39 of the notches are enlarged to receive the heads 40 of the lock dogs which heads are further enlarged to form shoulders 41 which are supported on the upper end surface 42 of the body. Each lock dog has spaced upward extensions or

fingers

43, 44 and 45 which are received in downwardly facing notches 46 of a positioning ring 47 whose upper end abuts the lower end of the upper sub 11. The outer upward extensions or

fingers

43 and 45 have curved surfaces 48 wh ch engage similarly curved surfaces of the notches in WhlCh they are disposed whereby outward pivotal movement of the lower ends of the lock dogs 38 may take place. It will be noted that the shoulders 41 which rest on the upper end surface 42 of the body are also slightly curved to permit such movement.

Each lock dog has a projection or boss'49 at its lower end which provides oppositely facing stop shoulders 50 outwardly by a spring 55 whose ends are received in suitable recesses 56 and 57in the reduced end portion 16 of the body 17 and in the lock dog, respectively.

Each of the lock dogs is also provided in its lower end with a T-shaped lock notch 58 which is adapted to receive the upper locking portion 19 of the plunger 18. The lock dogs are held'in retracted position, when the flanges 59 of the locking portion are in the T-shaped lock notches 58' of the dogs, by the force exerted by the spring 24 which urges the plunger 18 upwardly.

The upper outer ends of the flanges 59 of the locking portion 19 are inclined downwardly and outwardly to provide lock surfaces 61 so that, when the lock dogs have been moved to expanded positions, the locking portion 19 may move upwardly to cause the lock surfaces to be dis posed between the lock dogs to hold them against inward movement to retracted position.

The flow sub 26 may be internally threaded at its lower end so that any desired well tool may be secured to the lower end of the anchoring means. For example, a packing mandrel (not shown) could be secured to the flow sub and a tubing extension could be secured to the packing mandrel so that various types of well operations such as sand washing, cleaning, circulating, cement and acid spotting and squeeze cementing could be performed.

In use, the desired well tool is attached to the lower end of the flow sub 26 and a running tool is secured to the upper sub 11 by means of the shear pins.13. The running tool, of course, is attached to a flexible line lowering mechanism so that the entire assembly may be lowered into the well. The lock dogs 38 are in their retracted positions, as shown in Figure 4, held by the engagement of the lock portion 19 of the plunger in the T-shaped lock notches of the lock dogs. The release dogs are free to move outwardly and are biased outwardly by the spring 24 so that their surfaces 32 engage the internal surfaces of the well tubing during downward movement of the anchoring means.

When the anchoring means reaches the desired location in the well tubing, an upward pull is imparted to the flexible line until the outer ends of the release dogs engage in a coupling recess (Fig. 3) and abut the lower edge 52 of an upper tubing section. A further upward pull on the flexible line causes the body 17 and the lock dogs 38 to move upwardly with respect to the plunger 18 which is held stationary by the engagement of the release dogs with the lower edge 52 of the tubing section. As a result, the flanges 59 of the H-shaped locking portion 19 are disengaged from the T-shaped lock notches 58 in the lock dogs. The lock dogs are moved outwardly by the springs 55 to the position shown in Figure 6, wherein they abut the inner surface of the upper tubing section. The lock dogs are then disposed above the locking portion 19and are free to move outwardly and inwardly since their lower ends are disposed above the locking portion 19 of the plunger.

The whole assembly is then lowered until the bosses 49 of the lock dogs enter into the coupling recess 54, the

release dogs

21 and 22 being cammed inwardly as their ends move below the recess. Downward movement is then stopped by the engagement of the stop shoulders 51 of the lock dogs with the upper end 53 of the lower tubing section, and upward movement is prevented by the engagement of the stop shoulders 50 of the lock dogs with the lower end 52 of the upper section.

With the lock dogs in such expanded position, the plunger 18 may be moved upwardly by the spring 24 to position the locking surfaces 61 between the lock dogs and thus lock them in expanded position. Since the curved surfaces 32 at the upper outer ends of the release dogs engage and ride on the inner surface of the well tubing, the release dogs will slide downwardly in said tubing to a position below the coupling recess as the whole assembly is lowered to engage the stop shoulders of the bosses of the lock dogs in the coupling recess, and

4 the release dogs will not interfere with the upward movement of the plunger between the'lock dogsto locksaid lock dogs in expanded position with their bosses 49 engaged in the coupling recess.

A strong upward pull or jar is then imparted to the flexible line to shear the shear pins 13 and disconnect the running tool from the top sub 11, whereupon the running tool may be removed from the well, leaving the anchor means locked in position in the well tubing.

It will be seen that the anchoring means is positively held against either upward or downward movement since the locking surfaces 61 positively hold the lock dogs in expanded positions.

It will be apparent now that a new and improved well tool anchoring means has been illustrated and described which includes a body 17 on which are movably mounted lock dogs 38 positively held in retracted or expanded positions by a locking portion 19 of a plunger 18 mounted for longitudinal movement in the body. It will also be seen that

release dogs

21 and 22 connected to the plunger are engageable in a desired coupling recess of a well tubing to move the plunger downwardly to free the lock dogs for movement to expanded positions. Moreover, it will be apparent that the locking portion 19 of the plunger is movable upwardly between the lock dogs by the spring 24, after the lock dogs have moved to expanded positions, to lock said lock dogs positively in the expanded positions.

When it is desired to remove the anchoring means from the well tubing, a fishing tool is lowered into the well which tool contacts the upper end of the plunger 18 and forces it downwardly into the body 17. This downward movement of the plunger moves the release dogs 21 and 22, which are connected to said plunger, downwardly with said plunger and causes the release dogs to move to retracted positions since they are moved downwardly in the body 17, their outer edges contacting the lower edges of the lateral apertures 23a and thus being cammed inwardly during downward movement relative to the body. The lock dogs are also freed to move to retracted position, since the locking portion 19 is moved downwardly from between the lock dogs. The upper stop shoulders 50 of the lock dogs are inclined downwardly and outwardly so that the lock dogs will now be cammed inwardly when the stop shoulders contact obstructions during upward movement in the well tubing.

The fishing tool is also provided wtih a gripping means which engages the undercut annular flange 62 on the upper sub and thus permits raising of the anchor means when the fishing tool is raised. Such engagement of the gripping means with the flange 62 also positively holds the plunger in the lowered position just described, to permit the tool to be removed from the well.

It will be seen that an anchoring means for well tools has been provided which can be lowered into a well tubing by means of a flexible line and which can be positively locked in position against either upward or downward movement in the well tubing at any internal recess of the well tubing, and which can be removed from the well tubing by means of a fishing tool on a flexible line.

The foregoing description of the invention is explanatory only, and changes in the details of the construction illustrated may be made by those skilled in the art, within the scope of the appended claims, without departing from the spirit of the invention.

What I claim and desire to secure by Letters Patent is:

1. An anchoring means for well tools including: an elongate tubular body; a plurality of lock dogs mounted on said tubular body for lateral movement between rctracted and expanded position; movable means longitudinally movable in said body and having first locking means thereon for locking said lock dogs in said retracted position and having second locking means thereon for locking said lock dogs in said expanded position; biasing means carried by the body and acting on the movable means to move said movable means to position the locking means on said movable means in locking positions, each of said locking means being engageable with said lock dogs only when the other of said locking means is disengaged from locking engagement with said lock dogs; and release means connected with said movable means and engageable with a well tubing to move said movable means longitudinally to move said first locking means thereon out of position holding said lock dogs retracted to permit said dogs to move toward expanded position, whereupon said biasing means may move said movable means longitudinally in the opposite direction to position said second locking means thereon in position locking said dogs expanded.

2. An anchoring means for well tools insertable within well tubing and including: an elongate tubular body; a plurality of lock dogs mounted on said tubular body for lateral movement between retracted and expanded positions; movable means longitudinally movable in said body and having first locking means thereon for locking said lock dogs in said retracted position and having second locking means thereon for locking said lock dogs in said expanded position; biasing means carried by the body and biasing said movable means to position the locking means on said movable means in locking position; and release means connected to said movable means and having a portion projecting laterally therefrom whereby said projecting portion is engageable with a downwardly facing shoulder of a well tubing to cause downward longitudinal movement of said movable means relative to said tubular body upon upward movement of said tubular body in said well tubing to disengage said first locking means on said movable means from said lock dogs to permit said lock dogs to move toward expanded position; said biasing means moving said movable means upwardly relative to said tubular body to move said second locking means into engagement with said lock dogs to hold said lock dogs in expanded position after said lock dogs have moved to expanded position.

3. An anchoring means for well tools insertable within well tubing and including: an elongate tubular body; a plurality of lock dogs mounted on said tubular body for lateral movement between retracted and expanded positions; movable means longitudinally movable in said body and having first locking means thereon for locking said lock dogs in said retracted position and having second locking means thereon for locking said lock dogs in said expanded position; biasing means carried by the body and biasing said movable means to position the locking means on said movable means in locking position; and release means connected to said movable means and having a portion projecting laterally therefrom whereby said projecting portion is engageable with a downwardly facing shoulder of a-well tubing to cause downward longitudinal movement of said movable means relative to said tubular body upon upward movement of said tubular body in said well tubing to disengage said first locking means on said movable means from said lock dogs to permit said lock dogs to move toward expanded position; said biasing means moving said movable means upwardly relative to said tubular body to move said second locking means into engagement with said lock dogs to hold said lock dogs in expanded position after said lock dogs have moved to expanded position, said movable means having an upper end portion extending above said tubular body whereby said movable means may be moved downwardly relative to said tubular body to free said lock dogs for movement from expanded position toward retracted position.

4. An anchoring means for well tools insertable within well tubing and including: an elongate tubular body having a central longitudinal bore and spaced pairs of opposed lateral openings communicating with the central bore; a pair of lock dogs mounted in one pair of said opposed lateral openings for movement between retracted and expanded positions; a central member mounted for longitudinal movement in said tubular body and having first locking means engageable with said lock dogs for locking said lock dogs in retracted position and having second locking means separately engageable with said lock dogs for locking said lock dogs in expanded position; a pair of released dogs disposed in another pair of said lateral openings in said body and having their inner ends connected with said central member and their free ends swingable outwardly through said lateral openings to positions to engage a downwardly facing shoulder of a well tubing upon upward movement of said body in said tubing, such engagement of said release dogs with said downwardly facing shoulder moving said central member downwardly relative to said lock dogs to move said first locking means out of locking engagement with said lock dogs; and means biasing said central member upwardly in said body whereby said second locking means is yieldingly biased toward locking engagement with said lock dogs.

5. Ananchoring means for well tools insertable within well tubing and including: an elongate tubular body having a central longitudinal bore and spaced pairs of opposed lateral openings communicating with the central bore; a pair of lock dogs mounted in one pair of said opposed lateral openings for movement between retracted and expanded positions; a central member mounted for longitudinal movement in said tubular body and having first locking means engageable with said lock dogs for locking said lock dogs in, retracted position and having second locking means separately engageable with said lock dogs for locking said lock dogs in expanded position; a pair of release dogs disposed in another pair of said lateral openings in said body and having their inner ends connected with said central member and their free ends swingable outwardly through said lateral openings to positions to engage a downwardly facing shoulder of a well tubing upon upward movement of said body in said tubing, such engagement of said release dogs with said downwardly facing shoulder moving said central member downwardly relative to said lock dogs to move said first locking means out of locking engagement with said lock dogs; and means biasing said central member upwardly in said body whereby said second locking means is yieldingly biased toward locking engagement with said lock dogs; said lock dogs having downwardly opening lock notches, said first locking means on said central member engaging in said lock notches to hold said lock dogs in retracted position and being movable out of said notches to permit said lock dogs to move to expanded position.

6. An anchoring means for well tools insertable within well tubing and including: an elongate tubular body having a central longitudinal bore and spaced pairs of opposed lateral openings communicating with the central bore; a pair of lock dogs mounted in one pair of said opposed lateral openings for movement between retracted and expanded positions; a central member mounted for longitudinal movement in said tubular body and having first locking means engageable with said lock dogs for locking said lock dogs in retracted position and having second locking means separately engageable with said lock dogs for locking said lock dogs in expanded position; a pair of release dogs disposed in another pair of said lateral openings in said body and having their inner ends connected with said central member and their free ends swingable outwardly through said lateral openings to positions to engage a downwardly facing shoulder of a well tubing upon upward movement of said body in said tubing, such engagement of said release dogs with said downwardly facing shoulder moving said central member downwardly relative to said lock dogs to move said first locking means out of locking engagement with said lock dogs; and means biasing said central member upwardly in said body whereby said second locking means is yieldingly biased toward locking engagement with said lock dogs; said lock dogs having downwardly openinglock' notches, said first locking means on said central member engaging in said lock notches to hold said lock dogs in retracted position and being movable out of said notches to permit said lock dogs to move to expanded position; said second locking means on said central memher having downwardlyand outwardly inclined lock surfaces disposed to be moved between said lock dogs when said lock dogs are in expanded position to engage said lock dogs and prevent movement of said lock dogs toward retracted position.

7. An anchoring means for well tools insertable within well tubing andincluding: an elongate tubular body having a central longitudinal bore and spaced pairs of opposed lateral openings communicating with the central bore; a pair of lock dogsmounted in one pair of said opposed lateral openings for movement between retracted and expanded positions; a central member mounted for longitudinal movement in said tubular body and having first locking means engageable with said lock dogs for locking said lock dogs in retracted position and having second locking means separately engageable with said lock dogs for locking said lock dogs in expanded position; a pair of release dogs disposed in another pair of said lateral openings in said body and having their inner ends connected with said central member and their free ends swingable outwardly through said lateral openings to positions to engage a downwardly facing shoulder of a well tubing upon upward movement ofsaid body in said tubing, such engagement of said release dogs with said downwardly facing shoulder moving said central member downwardly relative to said lock dogs to move said first locking means out of locking engagement with said lock dogs; and means biasing said central member upwardly in said body whereby said second locking means is yieldingly biased toward locking engagement with said lock dogs; said lock dogs having downwardly opening lock notches, said first locking means on said central member engaging in said lock notches to hold said lock dogs in retracted position and being movable out of said notches to permit said lockydogs to move to expanded position; said second locking means on said central member having downwardly and outwardly inclined lock surfaces disposed to be moved between said lock dogs when said lock dogs are in expanded position to engage said lock dogs and prevent movement of said lock dogs toward retracted position; said central member having an upper end portion extending upwardly above said tubular body whereby said central member may-be moved downwardly relative to said tubular body to move said second locking means downwardly from locking engagement between said lock dogs to free said lock dogs for movement from expanded position toward retracted position.

8. An anchoring means for well tools insertable within well tubing and including: an elongate tubular body having a central longitudinal bore and spaced pairs of opposed lateral openings communicating with the central bore; a pair of lock dogs mounted in one pair of said opposed lateral openings for movement between retracted and expanded positions; a central member mounted for longitudinal movement in said tubular body and having first locking means engageable with said lock dogs for locking said lock dogs in retracted position and having second locking means separately engageable with said lock dogs for locking said lock dogs in expanded position; a pair of release dogs disposed in another pair of said lateral openings in said body and having their inner ends connected with said central member and their free ends swingable outwardly through said lateral openings to positions to engage a downwardly facing shoulder of a well tubing upon upward movement of said body in said tubing, such engagement of said release dogs with said downwardly facing shoulder: moving said central member downwardly relative to said lock dogs tomove said first locking means out of locking engagement with said lock dogs; means biasing said central member upwardly in said body whereby said second locking means is yieldingly biased toward locking engagement with said lock dogs; and means yicldingly biasing said lock dogs toward expanded position.

9. An anchoring means for well tools insertable within Well tubing and including: an elongate tubular body having a central longitudinal bore and spaced pairs of opposed lateral openings communicating with the central bore; a pair of lock dogs mounted in one pair of said opposed lateral openings for movement between retracted and expanded positions; a central member mounted for longitudinal movement in said tubular body and having first locking means engageable with said lock dogs for locking said lock dogs in retracted position and having second locking means separately engageable with said lock dogs for locking said vlock dogs in expanded position; a pair of release dogs disposed in another pair of said lateral openings in said body and having their inner ends connected with said central member and their free ends swingable outwardly through said lateral openings to positions to engage a downwardly facing shoulder of a well tubing upon upward movement of said body in said tubing, such engagement of said release dogs with said downwardly facing shoulder moving said central member downwardly relative to said lock dogs to move said first locking means out of locking engagement with said lock dogs; means biasing said central member upwardly in said body whereby said second locking means is yieldingly biased toward locking engage ment with said lock dogs; said lock dogs having downwardly opening lock notches, and first locking means on said central member engaging in said lock notches to hold said lock dogs in retracted position and being movable out of said notches to permit said lock dogs to move to expanded position; and means yieldingly biasing said lock dogs toward expanded position.

10. An anchoring means for well tools insertable within well tubing and including: an elongate tubular body having a central longitudinal bore and spaced pairs of opposed lateral openings communicating with the central bore; a pair of lock dogs mounted in one pair of said opposed lateral openings for movement between retracted and expanded positions; a central member mounted for longitudinal movement in said tubular body and having first locking means engageable with said lock dogs for locking said lock dogs in retracted position and having second locking means separately engageable with said lock dogs for locking said lock dogs in expanded position; a pair of release dogs disposed in another pair of said lateral openings in said body and having their inner ends connected with said central member and their free ends swingable outwardly through said lateral openings to positions to engage a downwardly t'acing shoulder of a well tubing upon upward movement of said body in said tubing, such engagement of said release dogs with said downwardly facing shoulder moving said central member downwardly relative to said lock dogs to move said first locking means out of locking engagement with said lock dogs; and means biasing said central member upwardly in said body whereby said second locking means is yieldingly biased toward locking engagement with said lock dogs; said lock dogs having downwardly opening lock notches, said first locking means on said central member engaging in said lock notches to hold said lock dogs in retracted position and being movable out of said notches to permit said lock dogs to move to expanded position; said second locking means on said central member having downwardly and outwardly inclined lock surfaces disposed to be moved between said lock dogs when said lock dogs are in expanded position to engage said lock dogs and prevent movement of said lock dogs toward retracted position;

and means yieldingly biasing said lock dogs toward expanded position.

11. An anchoring means for well tools including: an elongate tubular body having a plurality of spaced lateral apertures formed therein; a central member extending downwardly into and movable longitudinally in said tubular body; a pair of release dogs pivotally connected to said central member and having their free ends extendable outwardly through a pair of said lateral apertures in said tubular body; biasing means in said tubular body engaging said movable member to move said movable member and said release dogs upwardly in said body, said release dogs when moved upwardly with said central member having their free ends swingable outwardly and downwardly through the apertures in said tubular body; a pair of lock dogs mounted on said tubular body for movement between retracted and expanded positions; first locking means on said central member engageable with said lock dogs for holding said lock dogs in retracted position; and second locking means on said central member engageable with said lock dogs for locking said lock dogs in expanded position; said first and second locking means being separately engageable with said lock dogs, whereby said second locking means is engageable with said lock dogs only when said first locking means is disengaged from locking engagement with said lock dogs.

12. An anchoring means for well tools insertable within well tubing and including: an elongate tubular body having a pair of lateral apertures formed therein communicating with the interior of said body; a central member extending downwardly into and movable longitudinally in said tubular body; a pair of release dogs pivotally connected to said central member and having upper free ends extendable outwardly through said lateral apertures in said body; means in said tubular body biasing said central member upwardly in said body; a pair of lock dogs mounted on said tubular body for lateral movement between retracted and expanded positions; said lock dogs having inner portions exposed in said body; first locking means on said central member engageable with said lock dogs for holding said lock dogs in retracted position; said locking means on said central member engageable with said lock dogs for locking said lock dogs in expanded position, said release dogs being engageable with a downwardly facing shoulder of a Well tubing to move said central member downwardly in said tubular member to move said first locking means downwardly out of locking engagement with said lock dogs upon upward movement of said body in said well tubing to freesaid lock dogs for movement to expanded position; said means biasing said central member upwardly also then biasing said second lock means to engagement with said lock dogs to lock said lock dogs expanded, said second locking means being engageable with said lock dogs only when said first locking means is disengaged from locking engagement with said lock dogs; and means biasing said lock dogs toward expanded position.

References Cited in the file of this patent UNITED STATES PATENTS 2,392,244 Hooser Ian. 1, 1946 UNITED STATES PATENT OFFICE CETIFICAT EQ'HUN Patent Noe 2,856,007 Qotober 1.4, 1.958

John V0 Fredd It is herebir certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 10, line 11 for "said locking means" read m second locking means =0 Signed and sealed this 27th day of January 1959.,

(SEAL) Attest:

KARL H q AXLINE V ROBERT C. WATSON Attesting @fficor Commissioner of Patents