Method and apparatus for annulus pressure responsive circulation and tester valve manipulation

A releasably locked closed circulation valve is introduced into a well bore as part of a drill string. The annulus between the drill string and the well bore, or casing affixed to the well bore, is sealed. Pressure is applied to the annulus and the valve unlocks and opens once the annulus pressure reaches a certain level to allow circulation between the annulus and the interior of the drill string. An optional locking device preferably locks the opened valve in the open position. A second embodiment includes a tester valve simultaneously operable with the circulation valve.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a manipulation technique for valves of oil well 
test strings. 
2. Description of the Prior Art 
Annulus pressure responsive (hereafter called "APR") test-string 
manipulation is a relatively recent development in the art of oil well 
formation testing. U.S. Pat. No. 3,664,415 to Wray and Petty, assigned to 
the assignee of this invention, in 1972 disclosed a formation testing 
method and apparatus using variations in well annulus pressure to control 
the valving operation of a testing tool to entrap a formation sample. In 
formation testing, it is desirable to have a circulation valve, so that 
excess formation fluids present in the test string after testing may be 
forced out by pumping drilling mud or other displacement fluid down the 
well annulus and into the interior of the test string through the reverse 
circulation valve and upward toward the surface through the interior of 
the test string. This operation is called "reverse circulation." 
A circulation valve is also desirable to allow a flow path for fluids 
trapped in a test string above a closed valve, such as a tester valve for 
taking closed-in pressures, so that such fluids may pass into the wellbore 
upon pulling the pipe string from the well. This avoids having to contend 
with such well fluids at the wellhead. It would be a most disagreeable 
task to have to separate thousands of feet of pipe sections full of well 
fluids due to the absence of a properly functioning reverse circulation 
valve capable of allowing the fluids to "dump" into the well as noted 
above. 
Four types of reverse circulation valves are currently used in test 
strings: the rotating valve, the impact-sub valve, the reciprocal valve 
and the pump-out plug valve. 
The rotating valve is operated by rotation of the test string to open a 
reverse circulation port. This requires opening of blow-out preventer rams 
and rotating the pipe, which can be difficult if the pipe is in a bind as 
in the case of a deviated hole, and which could be catastrophic should the 
well "blow" during the rotational operation. Likewise, a reciprocally 
operated valve is subject to difficulties in deviated holes. 
An impact-sub type circulating valve requires dropping a bar which might 
hit ledges inside the pipe or have to fall through very viscous fluid and 
such a sub must be placed above any blind-type valve in the string. 
The pump-out type circulating valve might require internal pressure 
significantly higher than annulus pressure in order to open. In cases 
where annulus pressure is already high, such as where APR test tools are 
used, or it is undesirable to load the running string for hydraulic 
pressure application, a pump-out type valve might not be desirable. 
Considering said limitations, APR circulating valves have been developed to 
overcome the above noted difficulties, which are especially important in 
offshore oil well formation testing, and so as to be compatible with other 
APR testing tools and operable by essentially the same surface equipment. 
One solution to the above problems is a pressurized gas-biased annulus 
pressure responsive reverse circulating valve operated by multiple 
pressurizations and depressurizations of the well annulus as disclosed in 
pending application Ser. No. 288,187 by Holden et al., filed Sept. 11, 
1972, now U.S. Pat. No. 3,850,250 issued Nov. 26, 1974 and assigned to the 
assignee of this application. 
Another solution to the above problems and others is provided by the 
apparatus of the present invention, which provides a simple, inexpensive, 
reliable APR valve. 
BRIEF SUMMARY OF THE INVENTION 
The invention provides a method and apparatus for annulus pressure 
responsive valve manipulation. The method comprises the steps of 
introducing a closed substantially unbiased circulation valve into a well 
bore maintaining the valve in the closed position while pressurizing the 
well annulus, opening the valve in response to a predetermined annulus 
pressure, and maintaining said valve in the open position. The apparatus 
comprises a housing having an axial passage therethrough and a radial port 
communicating the exterior of the housing with the axial passage; sleeve 
means, carried by the housing; a first locking means, connecting said 
housing and said sleeve means for holding said sleeve means in a first 
position; and piston means, attached to said sleeve means for moving said 
sleeve to a second position.

Referring to FIG. 1, a pipe string 1 can be suspended from a subsea test 
tree 2 connected to a floating vessel 3 by conduit 4. Pipe string 1 
includes pipe 5, supporting slip joint 6 and slip joint safety valve 7 
which in turn supports pipe 8 connected to and supporting an APR 
circulating valve 9. APR circulating valve 9 is in turn connected to and 
supports an APR tester valve 10 which can be of the type disclosed in U.S. 
Pat. No. 3,664,415, application Ser. No. 443,599, filed Feb. 19, 1974, now 
U.S. Pat. No. 3,860,069, issued Jan. 14, 1975 or Ser. No. 412,881, filed 
Nov. 15, 1973, now U.S. Pat. No. 3,856,085, issued Dec. 24, 1974 all 
assigned to the assignee of this invention. APR testing valve 10 can 
support and be connected to a reciprocally operated tester valve 11 of the 
type as disclosed in U.S. Pat. No. 3,814,182, such reciprocally operated 
valve serving as a back-up tester valve in case of premature opening of 
APR tester valve 10. Reciprocally operated tester valve 10 can then be 
connected to auxiliary testing tools 12. Auxiliary testing tools 12 can 
include a packer 13 or other means for sealing the annulus 14 between the 
pipe string 1 and a surrounding well bore 15 in which said pipe string 1 
is suspended. When viewing FIG. 1, it will be understood that floating 
vessel 3 and the upper part 4a of conduit 4 are shown in a scale much 
reduced from that in which the lower part 4b of conduit 4 and the pipe 
string 1 and subsea tree 2 are shown. 
Referring now to FIG. 2, the structure of one preferred embodiment of the 
invention will be described in detail. FIG. 2 generally shows the APR 
circulating valve 9 of FIG. 1 in the closed position. APR circulating 
valve 9 comprises generally cylindrical housing 16, valve mandrel 17 
concentrically carried within housing 16, shear mechanism 18 attaching the 
housing 16 to the mandrel 17, a lock 19 carried by housing 16 and placed 
between housing 16 and mandrel 17, and a piston assembly 20 comprising 
certain portions of the mandrel 17 and housing 16. APR circulating valve 9 
is shown inverted in FIG. 1 to emphasize that valve 9 may be reversed 
without altering its function. 
Housing 16 comprises an upper adapter 21, a lower adapter 22, a central 
shell 23 therebetween and a bushing 24. 
Upper adapter 21 comprises a cylinder with a vertical axial bore 25 
therethrough, said bore 25 communicating with the bore of pipe 8 of FIG. 
1. The upper portion 26 of upper adapter 21 is threaded internally to 
allow for connection to pipe 8 of FIG. 1. An axial counterbore 27 of 
diameter larger than axial bore 25 is formed in the lower portion 28 of 
upper adapter 21 to produce an annular shoulder 29. A threaded external 
recess 30 is formed in the lower portion 28 of upper adapter 21. Annular 
shoulder 29 can be provided with mandrel rim cushion 93 to cushion upward 
movement of mandrel 17 within housing 16. 
Central shell 23 comprises a cylinder having upper internally threaded end 
31 and lower internally threaded end 32 and an axial bore 33 connecting 
said threaded ends 31 and 32. Upper threaded end 31 of central shell 23 is 
threadedly and externally connected to the threads of threaded recess 30 
of upper adapter 21, to produce an annular shoulder 34. 
Lower adapter 22 comprises a cylinder having an axial bore 35 of 
approximately the same diameter as axial bore 25 of upper adapter 21. The 
lower portion 36 of lower adapter 22 can have an axial counterbore 37 of 
diameter greater than axial bore 35. A first axial counterbore 39 of a 
diameter greater than axial bore 35 is formed in the head portion 38 of 
lower adapter 22 to produce a first annular ledge 40. A second axial 
counterbore 41, of diameter greater than axial counterbore 39, is formed 
in middle section 42 of the head portion 38 of lower adapter 22 to produce 
a second annular ledge 43. A third axial counterbore 44, of diameter 
greater than the diameter of second axial counterbore 41, is formed in the 
upper section 45 of the head portion 38 of lower adapter 22 to produce a 
third annular ledge 46. A fourth axial counterbore 47, of diameter greater 
than the diameter of third axial counterbore 44, is formed in the top 
section 48 of lower adapter 22 to produce a fourth annular ledge 49. The 
topmost section 50 of lower adapter 22 is internally threaded with 
internal threads 51 adapted to receive corresponding external threads 52 
of bushing 24. Head portion 38 of lower adapter 22 has an external recess 
53 extending from the top rim 54 of lower adapter 22 downward along the 
exterior of topmost section 50, top section 48, upper section 45 and the 
upper part 55 of middle section 42. The lower portion 56 of recess 53 has 
external threads 57 adapted to receive the lower threaded end 32 of 
central shell 23, while the upper portion 58 is smooth and has an outside 
diameter less than the diameter of bore 33 of central shell 23 so as to 
fit within bore 33 when internally threaded end 32 is threaded onto 
external threads 57. Middle section 42 of head portion 38 of lower adapter 
22 has a plurality of circulation ports 59 communicating second axial 
counterbore 41 with the exterior 60 of lower adapter 22, so as to allow 
fluid circulation therebetween when unobstructed. 
Bushing 24 is a cylinder with an axial bore 61 of a diameter substantially 
the same as the diameter of second axial counterbore 41 of head portion 38 
of lower adapter 22 and an external recess 62. Recess 62 has external 
threads 52 and is of axial length substantially the same as topmost 
section 50 of head portion 38 of lower adapter 22, so as to produce an 
annular shearing ledge 63 when threaded to internal threads 51 of topmost 
section 50. 
Mandrel 17 is a cylinder with an axial bore 64 of substantially the same 
diameter as both axial bore 25 of upper adapter 21 and axial bore 35 of 
lower adapter 22. Mandrel 17 is of axial length sufficient to reach from 
first annular ledge 40 of lower adapter 22 to above shoulder 34 of housing 
16. Mandrel 17 comprises an upper portion 65 and a lower portion 66 and a 
piston portion 67 therebetween. Mandrel 17 can be internally pressure 
balanced by making axial counterbores 27 and 39 of equal diameter and 
upper and lower portions 65 and 66 of equal annular cross-section. 
The upper portion 65 has an external diameter slightly less than the 
diameter of axial counterbore 27 of the lower portion 28 of upper adapter 
21 so as to allow upper portion 65 to slide within counterbore 27. An 
upper mandrel seal 68 is placed in a groove 75 just below the top rim 69 
of mandrel 17, so as to prevent fluid passage between upper portion 65 and 
axial counterbore 27. 
Lower portion 66 of valve mandrel 17 comprises a top section 70 and a 
bottom section 71. Top section 70 has an external diameter less than bore 
61 of bushing 24 and slightly less than the diameter of second axial 
counterbore 41 of head portion 38 of lower adapter 22, but of greater 
diameter than first axial counterbore 39 of head portion 31. Top section 
70 is of sufficient length to reach from the top rim 82 of bushing 24 to a 
distance X below fourth annular ledge 49, for reasons to be explained 
below. Bottom section 71 of lower portion 66 has an external diameter 
slightly less than the diameter of first axial counterbore 39, but greater 
than the diameter of axial bore 35 so that downward movement of the bottom 
rim 72 of valve mandrel 17 is limited by first annular ledge 40 of lower 
adapter 22. An annular locking shoulder 90 is formed between top secton 70 
and bottom section 71 due to the difference in their respective external 
diameters. Bottom section 71 is provided with a groove 73 containing a 
bottom mandrel seal 73 so as to prevent fluid passage between bottom 
section 71 and first axial counterbore 39 when valve mandrel 17 is in the 
position shown in FIG. 2. 
Piston portion 67 comprises a radial ledge 76 and piston seal 77. Radial 
ledge 76 projects radially outward from valve mandrel 17 betwen top 
portion 65 and bottom portion 66. Radial ledge 76 is of a diameter 
slightly less than the diameter of axial bore 33 of central shell 23 but 
greater than either axial bore 61 of bushing 24 or axial counterbore 27 of 
upper adapter 21. The external surface 78 of ledge 76 is provided with a 
groove 99 with a piston seal 77 therein, so that fluid passage between 
axial bore 33 and external surface 78 is prevented. The top surface 81 of 
radial ledge 76 can be provided with piston cushion 94 to cushion upward 
movement of radial ledge 76 as surface 81 approaches shoulder 34 of 
housing 16. Radial ledge 76 divides the annular chamber between mandrel 17 
and housing assembly 16 into an isolated upper low pressure chamber 79 and 
a lower annulus pressure chamber 80. Low pressure chamber 79 is axially 
located between shoulder 34 of housing 16 and the upper surface 81 of 
radial ledge 76 and radially located between upper portion 65 of mandrel 
17 and counterbore 33 of central shell 23. Annulus pressure chamber 80 is 
axially located between second annular ledge 43 of lower adapter 22 and 
bottom surface 83 of radial ledge 76 and radially located between housing 
16 and lower portion 66 of mandrel 17. Annulus pressure chamber 80 is in 
fluid communication with well annulus 14 of FIG. 1 via port 59 of lower 
adapter 22 and via one or more pressurization ports 84 through central 
shell 23 at a point just above the level of top rim 82 of bushing 24 when 
assembled. Low pressure chamber 79 can be isolated from both annulus 14 
and axial bores 64 and 25. 
Lower portion 66 of valve mandrel 17 has one or more shear pin holes 85 
located at a point on lower portion 66 which is opposite fourth axial 
counterbore 47 of head portion 38 of lower adapter 22 when bottom rim 72 
of valve mandrel 17 is in contact with first annular ledge 40 of lower 
adapter 22. 
Referring to FIG. 2, shear mechanism 18 comprises shear pin holes 85, shear 
collar 86, shear pins 87, and annular shearing ledge 63. Shear collar 86 
is a cylinder with an axial bore 88 and a plurality of shearing holes 89 
communicating axial bore 88 with the external surface of shear collar 86. 
One or more shearing holes 89 of shear collar 86 is aligned with one or 
more shear pin holes 85 of lower portion 66 of valve mandrel 17 and one or 
more shear pins are each inserted into both a shearing hole 89 and an 
aligned shear pin hole 85 so as to shearably connect valve mandrel 17 to 
shear collar 86. The number of shear pins utilized can be varied as 
necessary to obtain a desired resistance to opening. The determination of 
this number would include such considerations as: hydrostatic pressure 
expected, operating pressure for other APR tools and pipe strength. Shear 
collar 86 is located between annular shearing surface 63 of bushing 24 of 
housing 16 and fourth annular ledge 49 of lower adapter 22, so that upward 
movement of shear collar 86 will be restrained by shearing surface 63. 
However, upward movement of valve mandrel 17 is not restrained by shearing 
surface 63 but rather by shear pins 87, so that sufficient upward force on 
lower surface 83 of radial ledge 76 of valve mandrel 17 will shear the 
shear pins 87 and allow mandrel 17 to move upwardly even though shear 
collar 86 continues to be restrained as above described. 
Referring to FIG. 2 and FIG. 7, the lock 19 comprises an annular locking 
shoulder 90 and a lock ring 91. Lock ring 91 is a split ring having an 
internal diameter, when fully expanded, at least as great as the external 
diameter of upper section 70 of the lower portion 66 of mandrel 17 and 
having a diameter when fully relaxed of as least as small as the external 
diameter of bottom section 71 of lower portion 66 of mandrel 17. Locking 
ring 91 is placed in third axial counterbore 44 of head portion 38 of 
lower adapter 22 and abuts third annular ledge 46 of lower adapter 22. 
Upward movement of lock ring 91 is restrained by shear collar 86 which is 
restrained by bushing 24 of housing 16. Thus when valve mandrel 17 moves 
upward, as shown in FIG. 3, lock ring 91 stays in place until valve 
mandrel 17 has moved, as shown in FIG. 3, more than a distance X, at which 
time the lock ring is adjacent the external surface 92 of bottom section 
71 of the lower portion 66 of mandrel 17 and therefore can relax 
(contract) and thereby pass under annular locking ledge 90 of valve 
mandrel 17. Downward movement is thereby restrained since locking ledge 90 
cannot be lowered past locking ring 91. 
Referring still to FIG. 2, piston assembly 20 comprises annular ledge 76, 
annulus pressure chamber 80, ports 84 and 59, seals 68, 74 and 77, and low 
pressure chamber 79. The structure and location of ledge 76, chambers 79 
and 80, ports 59 and 80, and seals 68, 74 and 77 have previously been 
described. As pressure in the well annulus 14 of FIG. 1 is increased, that 
pressure acts via ports 59 and 84 upon bottom surface 83 of annular ledge 
76 and upon annular locking ledge 90, thereby tending to force valve 
mandrel upward against the restraint of shear pins 87. Upper surface 81 is 
acted upon by only the negligible pressure of low pressure chamber 79. 
Referring to FIG. 1 and FIG. 4, an alternative embodiment of the APR 
circulating valve 9 of FIG. 1 so as to incorporate an APR tester valve 
will be described. Mandrel 17a has been split by threads 96 so as to 
facilitate disassembly thereof. Referring to FIG. 4, it will be noted also 
that counterbore 27 of the upper adapter 21 of FIG. 2 has been extended 
axially through upper adapter 21 to eliminate axial bore 25 and annular 
shoulder 29 so as to provide a less restricted fluid passageway through 
upper adapter 21. Upward movement of the mandrel 17a is thus restrained by 
upper annular surface 81 of radial ledge 76 and not by annular shoulder 
29. The upper portion 65 of mandrel 17a has been provided with an annular 
recess 95 to provide a space for the gas in low pressure chamber 79 when 
mandrel 17a is in its upper position. The upper section 70a of the bottom 
portion 66a of mandrel 17a has been provided with an annular recess 97 
from just below bottom surface 83 of radial ledge 76 down to just above 
shear pin holes 85, so as to increase the size of annulus pressure chamber 
80. Shear collar 86a has been enlarged from shear collar 86 of FIG. 1 so 
as to accept another row of shearing holes 89. This modified shear collar 
86a is shown in FIG. 6. Mandrel 17a has been provided with a corresponding 
additional row of shear pin holes 85 to allow greater pressures to be 
applied to the annulus 14 of FIG. 1 without shearing of shear pins 87. 
The major distinction of the valve of FIG. 4 from that of FIG. 2 is the 
addition of a tester valve feature for closing off axial bore 64a so as to 
allow the taking of a closed-in-pressure reading of the formation's 
ability to produce. In this instance APR tester valve 10 of FIG. 1 could 
be deleted unless desired for multiple closed-in-pressure readings. 
Looking to FIG. 4 it is seen that bottom section 71a of lower portion 66a 
of mandrel 17a is much longer than bottom portion 71, so as to incorporate 
a tester valve. Bottom portion 71a of mandrel 17a can have an axial bore 
102 of a diameter less than the diameter of axial bore 64a of the upper 
section 70a of the lower portion 66a of mandrel 17a. One or more 
circulation ports 100 extend radially through bottom section 71a, and are 
each so positioned as to be substantially aligned with a port 59 of 
housing 16a after upward movement of mandrel 17a as below described. 
Bottom section 71 a is also provided with one or more external grooves 103 
to assure the alignment of circulation ports 59 and 100, grooves 103 are 
adapted to receive a stud 104 or other projection to prevent rotation of 
the mandrel 17a relative the housing 16a. Bottom section 71a also has a 
tester port 105, for reasons below described. Mandrel 17a extends 
downwardly to bottom rim 101 which rests on a tester plug 106, described 
below. 
Housing 16a of FIG. 4 extends downwardly around bottom section 17a. Lower 
adapter 22 of FIG. 2 is replaced by nipple 107, which has a topmost 
section 50a, top section 48a, and middle section 42a substantially the 
same as that of lower adapter 22, but has a lower portion 36a much 
different. Lower portion 36a comprises a first region 108 and a second 
region 109. First region 108 can be provided with a stud hole 111 adapted 
to hold stud 104 and with external threads 112. Second region 109 is of 
reduced external diameter relative to first region 108 and contains tester 
port 113. Port 113 is aligned with tester port 105 of mandrel 17a so as to 
allow fluid communication between the exterior of region 109 and axial 
bore 102 of portion 71a of mandrel 17a. Second region 109 is also provided 
with internal threads 114 adapted to receive plug 106. 
A bottom adapter 115 is included in housing 16a of FIG. 4, to form a flow 
channel 116 and provide threads 117 for connection of other tools or pipe. 
Bottom adapter 115 comprises an upper section 117, middle section 118, and 
a lower section 119. Upper section 117 has an external diameter 
approximately the same as that of nipple 107 and is provided with internal 
threads 120 adapted to engage with threads 112 of nipple 107. Middle 
section 118 has an internal diameter sufficiently greater than the 
external diameter of second region 109 of lower portion 36a of nipple 107 
to allow annular flow channel 116 of approximately the same 
cross-sectional area as axial bore 102. Lower section 119 is provided with 
threads 117 as aforementioned. Plug 106 can be threaded to the interior of 
second region 109 of nipple 107. When so threaded, plug 106 blocks fluid 
passage through the lower end 121 of nipple 107, thus creating an open 
sleeve valve out of bottom portion 71a of mandrel 17a and second region 
109 of lower portion 36a of nipple 107. 
Referring to FIGS. 1, 2 and 3, the operation of APR circulating valve 9 
will be described. Referring first to FIG. 1, and by way of introduction 
to said operation of valve 9, drill string 1 is lowered into the well bore 
15 to a desired position for formation testing and testing is conducted by 
use of auxiliary testing tools 13, valves 9 and 10 and valve 11. Before 
this testing is begun, auxiliary testing tools 13 isolate the well annulus 
14 so as to allow the application of pressure to annulus 14 without 
affecting formations below, and to allow the annulus to be pressurized to 
operate an APR tool in drill string 1. After the formation is tested and 
reverse circulation is desired, or even if reverse circulation is desired 
without the formation having been tested, the annulus 14 is pressurized 
sufficiently to operate APR reverse circulation valve 9 of drill string 1. 
Referring now to FIGS. 1, 2, and 3, the specific operation of APR 
circulating valve 9 will be described. When annulus 14 is pressurized, it 
can be seen that such pressure will act upon bottom surface 83 of radial 
ledge 76 of valve mandrel 17, since ports 59 and 84 in housing 16 allow 
fluid communication between annulus 14 and surface 83. This pressure 
creates an upward force on mandrel 17, which in turn puts a shear force on 
shear pins 87, due to the restraint of shear pins 87 by shear collar 86, 
as previously described. The magnitude of the annulus pressure necessary 
to shear the shear pins 87 depends on the number of shear pins 87, and 
this number would have been set at an appropriate figure in consideration 
of hydrostatic pressure, operating pressures of other APR tools and pipe 
strength. When such shear force reaches a level in excess of the shear 
strength of shear pins 87, the shear pins 87 are sheared and, as shown in 
FIG. 3, mandrel 17a moves upward under the motive force of the annulus 
pressure upon surface 83, to uncover circulation port 59 and thereby place 
axial bores 64, 35 and 27 in fluid communication with annulus 14, thereby 
allowing circulation between annulus 14 and the internal bore of drill 
string 1 of FIG. 1. 
This upward movement of mandrel 17 expands annulus pressure chamber 80 and 
contracts low pressure chamber 79, since seal 77 prevents fluid passage 
therebeteen, as previously described. When locking shoulder 90 of lower 
portion 66 of valve mandrel 17 passes upward a sufficient distance to be 
above locking ring 91, ring 91 will contract and seat under shoulder 90 
yet still be seated on third annular ledge 46 of lower adapter 22 of 
housing 16. Locking ring 91, in this position will prevent downward 
movement of mandrel 17. Since mandrel 17 is now locked-open the annulus 
pressure operating on shoulder 83 may be reduced completely without valve 
mandrel 17 recovering the circulation port 59. 
Looking now to FIGS. 4 and 5, it will be understood that the operation of 
the valve 9a is as described above for FIG. 2 with respect to the portion 
of valve 9a above circulation port 59. However, in valve 9a mandrel 17a 
also includes one or more tester ports 105 each in communication with a 
corresponding tester port 113 in housing 16. When plug 106 is installed in 
lower end 121 of nipple 107 and mandrel 17a moves upwardly in response to 
annulus pressure exceeding a predetermined magnitude tester port 105 moves 
upwardly out of alignment with tester port 113, thus blocking fluid 
passage from flow channel 116 into axial bore 102, thus isolating interior 
of the portion of pipe string 1 below tester port 113 from axial bore 102 
and the interior of the portion of pipe string 1 above tester port 113. 
This isolates the formation so that a closed-in-pressure reading may be 
taken to help determine the formation's ability to produce. 
It will be understood that the shear mechanism 18 described in detail could 
be replaced by a tension sleeve, collet spring or other equivalent 
attachment capable of releasing only after a given force is applied 
thereto. Also, it will be understood that the lock 19, which is described 
operates by means of a contracting locking ring 91, could be replaced by a 
ratchet mechanism, or any other device capable of limiting movement to one 
direction. Also, pressurizing port 84 is optional, since circulation port 
59 can allow fluid communication between the same surfaces. Port 84 is a 
redundancy built in to assure operation. As seen by comparison of FIG. 2 
and FIG. 4, annular shoulder 29 is not required, but may be redundantly 
added as a back-up feature. Similarly, cushions 93 and 94 are not 
mandatory but are added only for longer life and higher opening pressure 
capabilities. Many such modifications will suggest themselves to one 
skilled in the art without departing from the broad scope of this 
invention. 
Whereas the present specification has described in detail two embodiments 
of the invention, this description has been for purposes of illustration 
only and it is to be understood that many modifications such as, but in no 
way limited to, those noted in the preceding paragraph and elsewhere 
throughout the present specification will suggest themselves to one 
skilled in the art and may be made without departing from the scope of the 
invention as defined by the appended claims and the broad range of 
equivalents to be accorded thereto.