Automatic blow-out preventor means

Sept. 21, 1965

C. B. COCHRAN ETAL

3,207,221

AUTOMATIC BLOW-OUT PREVENTOR MEANS

Filed March 21, 1963

Sheets-Sheet 1

<img file="US3207221A_D0001.tif" />

ATTORNEY

Sept. 21, 1965

C. B. COCHRAN ETAL

3,207,221

AUTOMATIC BLOW-OUT PREVENTOR MEANS

Filed March 21, 1963

Sheets-Sheet 2

<img file="US3207221A_D0002.tif" />

ATTORNEY

Sept. 21, 1965

C. B. COCHRAN ETAL

3,207,221

AUTOMATIC BLOW-OUT PREVENTOR MEANS

Filed March 21, 1963

Sheets-Sheet 3

<img file="US3207221A_D0003.tif" />

ATTORNEY

Sept. 21, 1965

C. B. COCHRAN ETAL

3,207,221

AUTOMATIC BLOW-OUT PREVENTOR MEANS

Filed March 21, 1963

Sheets-Sheet 4

<img file="US3207221A_D0004.tif" />

:. EDWARDS J/?.

INVENTOR.

BY

Sept. 21, 1965

3,207,221

C. B. COCHRAN ETAL

AUTOMATIC BLOW-OUT PREVENTOR MEANS

Filed March 21, 1963

Sheets-Sheet 5

<img file="US3207221A_D0005.tif" />

Sept. 21, 1965

C. B. COCHRAN ETAL

3,207,221

AUTOMATIC BLOW-OUT PREVENTOR MEANS

Filed March 21, 1963

Sheets-Sheet 6

<img file="US3207221A_D0006.tif" />

<img file="US3207221A_D0007.tif" />

<img file="US3207221A_D0008.tif" />

ΑΤΤΟ&amp;.Λ/ΕΎ

United States Patent Office Patented Sept. 21, 1965

3,207,221

AUTOMATIC BLOW-OUT PREVENTOR MEANS Chudleigh B. Cochran, James D. Mott, and Joseph E.

Edwards, Jr., Houston, Tex., assignors, by mesne assignments, to Brown Oil Tools, Inc., Houston, Tex., a corporation of Texas

Filed Mar. 21,1963, Ser. No. 266,960

Claims. (Cl. 166—85)

This invention relates to automatic blow-out preventors for well pipes and more particularly to automatic stripper-type blow-out preventors.

In the operation of oil and gas wells, it is frequently necessary to run pipe strings, usually tubing strings, into and out of the well bores, while the well is under high fluid pressure. Various blow-out preventer means are conventionally employed to control the pressure while the pipe is being run. In one common system two or more conventional ram-type preventors are installed in spaced-apart relation on the wellhead to confine the pressure between the tubing and casing. At least two preventors are necessary because the tubing string being run is ordinarily made up of sections joined by collars larger in external diameter than the tubing sections. Since the collars cannot be passed through the rams while they are closed about the tubing, the rams must be worked alternately, releasing one to allow a collar to pass through while the other is confining the pressure in the annulus between the tubing and the casing. This operation is timeconsuming and can be hazardous because of the possibility that both preventors may accidentally be opened at the same time, resulting in a blow-out or other condition dangerous to the well personnel.

In another conventional system, stripper-type seals are employed. In this system, unlike the ram-type systems, the seals are not opened and closed about the tubing, but are continuous flexible bodies, usually having lip-type flanges which maintain continuous sealing engagement about the tubing by virtue of the well pressure exerted against the sealing flanges. In such systems, the seals are necessarily under the well pressure at all times, and passage of enlargements on the tubing, such as the collars, is effected by forcibly moving the collars through the strippers, the resiliency of the strippers being depended upon to yield sufficiently to permit passage of the collars. However, such strippers necessarily have a quite short life due to the excessive wear occasioned by the forcing of the tubing enlargements through the pressureloaded seal elements. In some cases, the destructive wear is so great that the strippers will not last out the running of a string of pipe of even moderate length, requiring shut-down of the operation to replace the strippers.

Accordingly, it is a primary object of this invention to provide blow-out preventor systems for use in running pipe strings which avoid the difficulties and disadvantages of the more conventional systems such as are enumerated above.

A principal object is to provide a blow-out preventor system employing a pair of seal elements in combination with sensing means responsive to enlargements on the tubing string being run in a well and cooperating with fluid-pressure-actuated operating means to automatically actuate the seal elements alternately to confine the annulus pressure between the casing and tubing, while contemporaneously automatically equalizing the pressure across the non-actuated seal elements in the advance of passage therethrough of the enlargement.

Another object is to provide a blow-out preventor system of the character described wherein the seal elements _g may be either ram-type or stripper-type, and wherein the operating means is hydraulically actuated.

In accordance with one embodiment of this invention, a structure is provided which includes a pair of longitudinally spaced stripper elements comprising resilient seal ₁₀ members adapted to sealingly engage a tubing string or other pipe which is being run into a well and to seal thereabout when subjected to the annulus pressure between the pipe string being run and the well casing. Associated with the strippers are sensing elements which are rejg sponsive to the passage of enlargements on the pipe or tubing string and which are operatively associated with operating means actuated by fluid pressure to alternately actuate one of the stripper elements to confine the fluid pressure while equalizing the pressure across the other 2Q stripper element in advance of the passage of the enlargement through the stripper element. The alternate actuation of the stripper elements is effected automatically by means of the sensing elements so that no manual manipulations are required to make sure that an enlargement 25 on the pipe or tubing string being run will not be caused to pass through a stripper element which is under pressure. At the same time, the other of the stripper elements will be under pressure sufficient to maintain the necessary seal between the tubing string and the casing. 3Q In another embodiment in accordance with this invention, the seal elements are of the conventional ram-type which are automatically actuated in the same manner and by the same enlargement-sensing and actuating elements as are used for the stripper-type embodiment.

In yet another embodiment a somewhat modified hydraulic device is employed for operating the seal elements in response to actuation by the enlargement-sensing elements.

Other and more specific objects and advantages of this 40 invention will become more readily apparent from the following detailed description when read in conjunction with the accompanying drawing which illustrates a useful embodiment in accordance with this invention.

In the drawing:

FIG. 1 is a view partly in section and partly diagrammatic illustrating a stripper blow-out preventor system in accordance with this invention;

FIGS. 2 and 3 are generally diagrammatic views illustrating successive stages in the operation of the device 50 while a tubing string is being run into a well;

FIGS. 4 and 5 are diagrammatic views similar to FIGS. 2 and 3 illustrating the positions of the parts when a tubing string is being pulled from a well;

FIG. 6 is a cross-sectional view taken generally along 55 line 6—6 of FIG. 1;

FIG. 7 is a cross-sectional view along line 7—7 of FIG. 1;

FIG. 8 is a perspective view of one of the control elements employed in the system;

FIGS. 9 and 10 are generally diagrammatic views generally similar to FIGS. 2 and 3 but substituting ram-type seal elements for the stripper-type elements;

FIG. 11 is a cross-sectional view taken generally along line 11—11 of FIG. 10; and

FIGS. 12 and 13 are views generally similar to FIGS. 2

3,307,221 and 3, but illustrating a modified form of hydraulic actuating system for the seal elements.

Referring first to FIGS. 1 to 8 of the drawing, the blowout preventor structure comprises a generally tubular housing, designated generally by the letter H, adapted to be mounted on a wellhead fitting F, which may be of any suitable type permitting the preventor housing H to be suitably supported in coaxial alignment with the bore of a well (not shown) but which, it will be understood, will be lined with the usual well casing (not shown). The housing structure is designed to receive a string of pipe P which may be run into, or pulled from, the well through the bore of housing H.

Pipe P, which may be a string of well tubing, comprises a plurality of pipe sections connected by collars C which form longitudinally spaced external enlargements about the pipe string.

Housing H is made up of a plurality of coaxial end-toend connected, generally tubular members which include upper and lower stripper seal units S_x and S₂, respectively, an upper enlargement-sensing unit E_t connected to the upper end of upper stripper seal unit Si and a lower sensing unit E₂ connected between the stripper units.

Stripper units Si and S₂ are substantially identical in construction, each comprising a metallic tubular body 10 and a tubular sealing element 11 concentrically mounted in the bore of body 10. Sealing element 11 is constructed of a generally conventional flexible resilient composition and has an inwardly projecting annular sealing portion 12 adapted to normally have slidable sealing contact with the exterior of pipe P. The ends of sealing element 11 are secured to metal upper and lower end rings 13 and 14, respectively. Upper end ring 13 has an external downwardly facing shoulder 15 engageable on an internal upwardly facing shoulder 16 in the bore of body 10. Lower end ring 14 seats against an upwardly facing internal shoulder 17 in body 10. A lock pin 18 is screwed through the wall of body 10 into a recess 19 in the lower end ring. The shouldered engagement between upper end ring 13 and body 10 and the cooperation between lower end ring 14, shoulder 17 and lock pin 18 serve to lock the end rings to body 10, holding them stationary while permitting seal elements 11 to radially expand and contract, as will appear hereinafter. The inner wall of body 10 opposite sealing element 11 is recessed to provide the annular chamber 20. One or more radial openings 21 are provided through lower end ring 14 to provide fluid pressure communication between chamber 20 and the annular space A defined between housing H and pipe P. It will be understood that annular space A is in communication with the well annulus (not shown), that is, the annular space between pipe P and the wall of the well into or out of which the pipe is being run.

The lower end of body 10 of lower stripper unit S₂ is provided with a threaded pin 22 by means of which housing H is threadedly secured to wellhead fitting F.

Upper and lower enlargement-sensing units E_x and E₂are also substantially identical in construction. Each includes a mounting collar 25 which forms a part of housing H and also functions to support the operative elements of the sensing unit. The upper mounting collar connects a guide nipple 26, which forms the uppermost element of housing H, in axially spaced relation to the upper end of body 10 of the upper stripper unit, thereby providing the annular space 27 therebetween.

Lower mounting collar 25 connects bodies 10 of the upper and lower stripper units in axially spaced relation to provide the annular space 28 therebetween.

The operative elements of the sensing units include a plurality of contact pads 30 mounted for limited radial movement in spaces 27 and 28. The contact pads are conveniently constructed as segments of a ring (FIG. 6) arranged to surround pipe P and may be formed with forwardly projecting portions 31 on their inner surfaces to provide the pipe contacting points. Any desired num4 ber of pads 30 may be employed. Three are shown in the illustrative embodiment. The top and bottom walls of spaces 27 and 28 are provided with opposed keeper lips 32 and 33, respectively, which are adapted to cooperate with oppositely extending flanges 34—34 at the rearward edges of the pads to confine the pads within spaces 27 and 28 while permitting limited radial movement of the pads sufficient to project portions 31 into contact with pipe P.

Each of the pads 30 is urged outwardly of spaces 27 and 28 toward pipe P by identical structures, each of which includes a hollow plunger 35 which extends radially through the mounting collar and is slidable therein. Plunger 35 has its inner end received in a socket 36 in the outer surface of pad 30 and its outer end enclosed by a cylinder 37 which is screwed into the exterior of the mounting collar. The outer end of cylinder 37 is closed by a cap 38 having a socket 39 to slidably receive the outer end of plunger 35. A coil spring 40 is mounted in socket 39 in compression between the end of the plunger and the bottom of the socket 30 toward pipe P.

Plunger 35 carries a sealed piston 41 slidable in cylinder 37 with the plunger and defining a pressure chamber 42 between the piston and cap 38. Pressure chamber 42 is adapted to contain a body of a suitable pressure fluid. A conduit 43 provides pressure fluid communication between chamber 42 and an annular pressure fluid reservoir 44 formed within the body of mounting collar 25. As the pressure fluid system which includes plunger 35 is a closed system, one of the several conduits 43 may be connected to a small accumulator 45 to accommodate excessive displacement of fluid in the pressure fluid system during operation of the device. A pipe 46 leads from conduit 43 of the upper sensing unit Ej to one of the inlet ports 48 of a four-way valve 47, of generally conventional rotary construction, having a ported plug 47α. A pipe 46α leads from conduit 43 of lower sensing unit E₂ to another inlet port 48α of valve 47.

A conduit 49 leads from one of the discharge ports 50 of valve 47 to one end of control valve, designated generally by the letter V, and a second conduit 51 leads from the other discharge port 50α of valve 47 to the opposite end of control valve V. In one position of plug 47α (FIGS. 1, 2 and 3) conduits 46 and 46α are placed in communication with conduits 49 and 51, respectively. In a second position of plug 47α (FIGS. 4 and 5), conduits 46 and 46α are put in communication with conduits 51 and 49, respectively.

Control valve V constitutes a portion of a second closed, fluid pressure system, referred to herein as the actuating system, which is adapted to actuate strippers 11 alternately in response to actuating signals received from the sensing units. The actuating system controls a pressure equalizing conduit 55, the opposite ends of which communicate through ports 56 in bodies 10 with pressure chambers 20 of the stripper units S_x and S₂. A generally conventional three-way rotary valve 57 (shown in perspective in FIG. 8) is mounted in conduit 55 and includes a casing 58 having three ports 58α, 586 and 58c, two of which, 58α and 586, are in communication with branches of conduit 55. Port 58c communicates with a bleed conduit 59. A plug member 60 is rotatably mounted in casing 58 and is adapted to oscillate between two positions for selectively placing chambers 20—20 in communication with each other or only upper chamber 20 with bleed conduit 59. Plug member 60 is driven by means of a shaft 61 connected to a vane motor 62 which is mounted in a casing 63 and is caused to oscillate by fluid pressure directed into casing 63 through one or the other of a pair of inlet ports 64 and 65 which are in communication with pressure fluid conduits 66 and 67, respectively, which lead from control valve V.

Control valve V is a generally conventional multi-port spool-type valve comprising a tubular casing 70 and a. spool-type valve member 71 slidable axially in the cas

3,207,221 ing. Valve member 71 is formed with a pair of enlargements 72—72 at its opposite ends and a third enlargement 73 intermediate the end enlargements, the several enlargements having slidable sealing engagement with the wall of casing 70. The three enlargements define between them a pair of annular passageways 74 and 75 which ⁵communicate, respectively, with outlet ports 76 and 77 at all positions of the spool member. Outlet ports 76 and 77 communicate with pressure fluid conduits 66 and 67, respectively. A pair of longitudinally spaced vent ports 78 and 79 are provided through the wall of casing ¹⁰70 and are longitudinally spaced so that only one of them will be in communication with one of the passageways 74 and 75 at any position of valve member 71. Thus, when valve member 71 is in the position shown in FIGS.

and 2, passageway 75 will be in communication with ¹⁵vent port 79, while passageway 74 will be cut off from vent port 78 by an end enlargement 72. When valve member 71 has been shifted to the opposite end of casing 70 (FIG. 3), passageway 74 will be in communication with vent port 78 while passageway 75 will be cut off from ²⁰communication with vent port 79. Vent ports 78 and 79 are connected to a common header 80 which leads to a pressure fluid accumulator tank 81.

An inlet port 82 communicates with valve casing 70 _ at substantially the mid-point thereof, being located to communicate with one or the other of passageways 74 and 75, depending upon the position of valve member 71. Inlet port 82 is connected to a pipe 83 which leads to tank 81 and has a pump 84 positioned therein to deliver fluid under pressure to valve V through inlet port 82.

Mounted on the opposite ends of valve casing 70 are pressure cylinders 85 and 86 in which are disposed pistons 87 and 88, respectively, mounted on rods 89 and 90, respectively, which slidably project through the end walls ₃₅of casing 70 into engagement with the opposite ends of valve member 71. Pistons 89 and 90 are biased outwardly with respect to ends of casing 70 by means of the springs 91. Cylinder 85 is in communication with conduit 49 and cylinder 86 with conduit 51, the cylinders thereby forming part of the closed pressure systems which include sensing elements Εχ and E₂.

The blow-out preventor is operated in the following manner: As seen in FIG. 1, pipe string P is in process of being run into a well through the blow-out preventor ₄₅structure herein described. At the stage shown, collar C has moved opposite pads 30 of the upper sensing element E_t and has forced the pads rearwardly against the pressure of springs 40, thereby moving pistons 41 rearwardly and displacing pressure fluid from chambers 42 through gQ conduits 43 into reservoir 44. Some of the displaced fluid will be forced through conduit 46 and through multiport valve 47 via ports 48 and 50 into conduit 49 which will deliver the displaced pressure fluid into cylinder 85. The pressure fluid will act on piston 87, driving valve 55 member 71 to the position shown in FIG. 1. This will place pressure fluid supply conduit 83 into communication with passageway 74 while passageway 75 is placed in communication with vent port 79. The pressure fluid will flow through passage 74 and thence through ports θθ 76 and conduit 66 against one side of vane motor 62, which will rotate plug 60 of valve 57 to the position shown in FIG. 1. The fluid in the other side of the vane motor will drain back through conduit 67, valve passageway 75 and manifold 80 to the storage tank 81. This θ5 movement of valve 57, as shown, will permit pressure chamber 20 of upper stripper unit Si to be vented through conduit 55 to bleed pipe 59 and will equalize the pressure in chamber 20 of upper stripper unit Sx with the atmosphere. At the same time, with valve plug 60 in the posi- γθ tion shown in FIG. 1, conduit 55 will be cut off from pressure chamber 20 of the lower stripper unit S₂, which will then be under the pressure of the well fluid in annulus A. As a result, stripper element 11 of the lower stripper unit S₂ will be actuated to form a fluid-tight seal about jg pipe P, thereby confining the annulus pressure at this point while the upper stripper unit is relieved of the well pressure through bleed pipe 59. As the pipe string moves downwardly, therefore, stripper element 11 of upper stripper unit δχ will relax, allowing collar C to pass through easily and without damage to the stripper element. FIG. 2 illustrates, diagrammatically, the positions of the several parts at the stage of operations just described, at which collar C has passed the upper sensing unit and is passing through the upper stripper unit Sx.

As the pipe string continues to move down and collar C passes the sensing pads of lower sensing unit E₂, the latter is activated to displace pressure fluid through conduits 43, 46α and 51 into cylinder 86, moving piston 88 in a direction to drive valve member 71 to the opposite end of casing 70, as seen in FIG. 3. When this occurs, passageway 75 will be placed into communication with pressure fluid from conduit 83 while passageway 74 is connected to vent passage 78. The pressure fluid will be transmitted through conduit 67 to the other side of vane motor 62, rotating plug 60 of valve 57 to the position shown in FIG. 3, at which pressure chambers 20 of both stripper units Sx and S₂ will be placed into communication with each other, applying annulus pressure to upper stripper unit Sx and thereby actuating the sealing element of the upper stripper unit to close the annulus between pipe P and housing H, while passing through port 21 and equalizing the pressure across the lower stripper unit. This will relieve the latter from the pressure load so that collar C may pass through the lower stripper element 11 without exerting any serious drag or destructive force thereon. When the next collar reaches sensing unit Εχ, the operations will be repeated, that is, lower stripper S₂ will be actuated to seal the well annulus about pipe P, while the pressure across the upper stripper unit is equalized with the atmosphere, freeing it for ready passage of the next collar.

To pull the string of pipe from the well under pressure, the only change required is to rotate plug 47α of valve 47 to the position shown in FIGS. 4 and 5. In this position, conduit 46α will be placed into communication with conduit 49 and conduit 51 will be placed into communication with conduit 46, and all other connections will be exactly as shown in FIGS. 1 to 3 and as previously described.

It will be assumed that collar C in FIG. 4 will have passed through lower stripper unit S₂ while the latter is under equalized pressure, as this was the case in order for the collar to have moved downwardly through the stripper initially. As collar C moves upwardly opposite the pads of lower sensing unit E₂, the latter will be actuated to displace pressure fluid through conduits 46α and 49 by way of valve plug 47α to cylinder 85, moving valve member 71 again to the position shown in FIG. 4, which is exactly the same position as in FIGS 1. and 2. In this position, the pressure fluid from tank 81 will be delivered from conduit 66 to vane motor 62, moving plug 60 to a position placing conduit 55 in communication with bleed pipe 59, while cutting off communication to lower pressure chamber 20. Whereupon, the lower stripper unit S₂ will be actuated by the annulus pressure to seal off the well annulus while the pressure across upper stripper unit Sx will be equalized with the atmosphere through bleed conduit 59. Thereupon, when the pipe string is pulled upwardly, collar C will pass through the upper stripper element, which will have been unloaded of its pressure and upon contacting the pads of upper sensing unit E_1; as shown in FIG. 5, the pressure fluid displaced thereby through conduit 46 and conduit 51 via plug 47α of valve 47 will enter cylinder 86 and act on piston 88, moving valve member 71 to the opposite position, shown in FIG. 5. Thereupon, pressure fluid from conduit 83 will flow through passageway 75 via conduit 67 to the other side of the vane motor 62, moving plug 60 of valve 57 to the position shown in

3,207,221

FIG. 5, whereby the annulus pressure will be communicated to the upper stripper unit Sj to actuate the stripper element therein to seal off the annulus between pipe P and housing H, while equalizing the pressure across the lower stripper unit S₂ in advance of the entry therein of the next collar on the pipe string. These operations will be repeated as each collar approaches each of the stripper units until the string of pipe has been withdrawn from the well.

In the foregoing description, the sensing units and the control elements are described as being actuated by means of a hydraulic pressure fluid. It will be readily evident, however, that one or both the sensing units and the control unit may be actuated with pneumatic pressure fluid. While this will require the use of pneumatic systems involving pilot valves and other conventional pneumatic equipment, the changes necessary to convert to use of a pneumatic fluid will be readily evident to those skilled in the art, and will involve no significant modifications of the invention herein disclosed.

It will be evident that in accordance with this invention a novel system is provided whereby two strippertype units may be employed as the blow-out preventors and are automatically operated to permit passage of enlargements on a pipe string when the pressure load is removed from one of the stripper units, the other being simultaneously actuated to seal off the annulus between the pipe string being run through the well bore and the wall of the well bore.

FIGS. 9, 10 and 11 illustrate a modification in which conventional ram-type sealing units, designated generally by the letters Ri and R₂, are substituted for the corresponding stripper-type units of the previously described embodiment. Each of the ram-type blow-out preventor units Rj and R₂ includes a casing 92 adapted for mounting transversely in housing H. A pair of opposed rams 93 are slidably mounted in casing 92 to seal off the annular space between pipe string P and housing H when the rams are advanced to engage about the pipe string. The rams are operated by means of pistons 94 secured to the outer ends of the rams and working in cylinders 95 formed in the outer ends of casing 92. Springs 96 normally bias the rams to the retracted position. Pressure fluid is supplied to cylinders 95 through a header 97 which, in unit R_b communicates with conduit 66, and in the case of unit R₂, with conduit 67.

Since rams Rj and R₂ constitute positive-type seals, the pressure equalizing connections comprising ports 56 and conduit 55 may be eliminated, together with rotary valve 57 and vane motor 62. Instead, conduits 66 and 67 are connected directly, as noted, to headers 97 of rams Rj and R₂, respectively.

With this arrangement, it will be seen that when upper sensing unit Ej is actuated by an enlargement, valve V will be actuated in exactly the same manner as previously described to deliver pressure fluid through conduit 67 to lower ram unit R₂, closing the latter about pipe P. This movement places upper ram unit Ri in communication through pipe 66 with return pipe 80 leading to the accumulator tank 81. The biasing spring 97 will cause retraction of rams 93 of ram unit Rj and thereby opens the seal to the passage of the enlargement.

When the enlargement engages the sensing element of sensing unit E₂, value V will be actuated, as previously described, to place conduit 66 in pressure communication with the pressure fluid supply, closing upper ram unit Ri about pipe P above the enlargement. At the same time, the pressure on the rams of ram unit R₂ will be relieved, allowing the latter to open for subsequent passage of the enlargement.

In pulling pipe, it will only be necessary to reverse valve 47, as previously described, the operation being otherwise exactly just as described.

FIGS. 12 and 13 illustrate still another modification, and in this modification, stripper units S₃ and S₄, cor responding to stripper units Si and S₂, respectively, are employed. The enlargement-sensing units Ei and E₂ are identical to those previously described. Pressure equalizing conduit 55 connecting ports 56 through valve 57 are employed in this embodiment exactly the same as in the first described embodiment. The vane motor 62 is likewise employed for operating valve 57, as is multiport valve 47. However, instead of the external source of pressure fluid, such as tank 81 and pump 84, and the multiport valve corresponding to valve V of the previously described embodiment, there is substituted a dual closed hydraulic system arrangement for operating vane motor 62. In this embodiment, conduit 46, which leads from upper sensing unit E_b connects to port 48 of valve 47 and thence via ports 50 to one end of a cylinder 100, the other end of which is connected, by means of a conduit 101, to one side of vane motor 62. Conduit 46α is similarly connected to port 48α of valve 47 .and thence via port 50α to conduit 51, which leads to one end of a second identical cylinder 100, the other end of which is connected by a conduit 101 to the other side of vane motor 62. Each cylinder 100 is divided intermediate its ends by a partition 102 having a central opening adapted to slidably receive a piston rod 103. The latter carries an upper piston 104 reciprocable in the portion of cylinder 100 on one side of partition 102, and a lower piston 105 reciprocable in the portion of cylinder 100 on the opposite side of partition 102. In each cylinder the upper piston 104 is biased away from partition 102 by means of a coil spring 106. The portion of cylinders 100 between lower pistons 105 and conduit 101 contain bodies of hydraulic fluid 107 which are adapted to flow back and forth through conduits 101 between the related sides of vane motor 62 and the communicating portions of the related cylinders 100. Thus, two closed hydraulic systems are provided, each including one side of vane motor 62 and the connected portion of the related cylinder 100. It will be seen that when one of the pistons is moved in the direction to compress the body of fluid 107, vane motor 62 will swing in one direction, while the body of fluid 107 in the other side of the vane motor will be forced back into the other cylinder 100, moving the pistons therein to the retracted position. When the pressure forces are reversed, the vane motor is swung in the opposite direction.

In operation: When upper sensing unit E_x is actuated by passage of a collar C, fluid pressure will be exerted through conduit 46 and ports 48 and 50 in valve 47, and thence through conduit 49 against piston 104 in the righthand one of cylinders 100. The piston will be forced downwardly (as viewed in the drawing), forcing the body of hydraulic fluid 107 therein to act upon the side of vane motor 62 which will move plug 60 in valve 57 to the position shown in FIG. 12, in which lower seal unit S₄ will be held under pressure, sealing off about pipe P. The annular space between the sealing units will be relieved through bleed pipe 59, thereby equalizing the pressure across the seal unit S₃. As collar C engages lower sensing unit E₂, after passing through upper seal unit S₃, the piston in the left hand one of the cylinders 100 will be forced downwardly, causing vane motor 62 to swing in the opposite direction and moving valve 57 to the position shown in FIG. 13, wherein pressure is equalized across lower seal unit S₄, while the annulus pressure is transmitted between the seal units to actuate the upper seal unit S3 to seal about pipe P after collar C has passed therethrough.

_ As in the previously described embodiments, when the pipe is being pulled from the well the only change necessary in the structure shown in FIGS. 12 and 13, is to change the position of valve 47 to connect pipe 49 to pipe 46α and conduit 46.

From the foregoing it will be seen that in each embodiment when running pipe into the well, the second or lower of the two sealing units is actuated first to seal off about the pipe and equalize the pressure across the first or

3,207,221 upper sealing unit. The first or upper sealing unit is actuated second in order to seal off about the pipe after the enlargement has passed it and thereby equalize the pressure across the second or lower of the two sealing units.

When pulling pipe from the well, positions of the seal units in order of their actuation is reversed. The upper seal unit becomes the second in order of passage by the enlargement but is actuated first, while the lower seal unit becomes the first in order of passage by the enlargement but is actuated second.

It will be evident, therefore, that the means employed to actuate the seal elements are arranged to successively actuate the seal elements in inverse order with respect to the direction of movement of the enlargement whereby to automatically equalize the pressure across each seal element as it is approached by the enlargement.

It will be understood that numerous changes and alterations may be made in the details of the illustrative embodiment within the scope of the appended claims but without departing from the spirit of this invention.