US 3416767 A
Description (OCR text may contain errors)
Dec. 17, 1968 L. BLAGG BLOWOUT PREVENTER 2 Sheets-Sheet 1 Filed Dec. 20, 1966 A eon 5/09;
Dec. 17, 1968 L. BLAGG BLOWOUT PREVENTER 2 Sheets-Sheet Filed Dec. 20, 1966 BY Y ' ATTO/PAj United States Patent 3,416,767 BLOWOUT PREVENT ER Leon Blagg, Channelview, Tex., assignor to Schlumberger Technology Corporation, Houston, Tex., a corporation of Texas Filed Dec. 20, 1966, Ser. No. 603,200 Claims. (Cl. 251-1) ABSTRACT OF THE DISCLOSURE This disclosure describes a blowout preventer for service on high-pressure wells in which either tubing or cablesuspended tools are disposed. The disclosed blowout preventer includes a pair of opposed rams that are movably mounted on opposite sides of a pressure housing and adapted to be brought together for sealing around the opposite sides of a suspension member extending through the housing between the rams. More particularly, an inner sealing member is movably mounted within each ram and is selectively operated by either a hydraulic or a manual actuator.
Accordingly, as will become more apparent, this invention relates to blowout preventers; and, more particularly, this invention pertains to new and improved blowout preventers having selectively operable sealing means adapted for movement independently of their closing rams.
For one reason or another, it is frequently necessary to periodically introduce various cable-suspended well tools or instruments into producing oil wells during the course of their life. In those instances where a well is flowing or contains fluids at high pressures, the upper end of the well casing is closed by suitable valving and special well-servicing equipment must, therefore, be provided to safely introduce and remove such tools or instruments. This well-servicing equipment typically includes an upright section of pipe or a riser for receiving the well tool which is mounted on top of a so-called blowout preventer" temporarily connected to the cut-off valves on the wellhead. A so-called lubricator having a stufiing box or line wiper on its other end is connected to the upper end of the riser to provide a pressure seal around the tools suspension cable at the point where it exits from the apparatus.
In this manner, while the well valves are closed, the well tool can be safely inserted into the riser and its suspension cable brought out through the lubricator and stufling box. Then, after the well valves are opened, the
well tool is lowered through the open blowout preventer and on into the well. Thus, so long as the lubricator and stuifing box maintain an adequate seal around the suspension member, there is little danger of high-pressure fluids escaping from the well. Should, however, some malfunction occur whereby the lubricator or stufling box is incapable of keeping the well under control, it may be necessary to quickly close the blowout preventer to provide a tight seal around the suspension member and completely seal-off the well.
A typical blowout preventer includes an upright pressure housing in which is mounted a pair of opposed horizontal rams adapted to be brought together around a suspension member. These rams are usually tubular with elastomeric sealing members being mounted in their axial bores. Vertical semi-circular grooves across the opposed forward faces of the rams and sealing members are suitably sized to tightly encircle the suspension cable passing therebetween once the blowout preventer is closed. To close certain types of blowout preventers, axially movable actuators are urged against the rear faces of these inner sealing members with sufiicient force t move both them and the rams inwardly together. Then, once the opposed for- 3,416,767 Patented Dec. 17, 1968 ward faces of the rams have engaged, additional force is applied on the rear of the inner sealing members to firmly seal their forward faces around the suspension member. To open a blowout preventer arranged in this manner, the increased axial forces on the sealing members are first relieved to allow the sealing members to relax before the blowout preventer is opened.
Although such blowout preventers, have been used with success, it has nevertheless been found that they will perform satisfactorily for only a very few operations before repairs must be made. The paramount reason for such frequent repairs appears to be that the forward ends of these inner elastomeric sealing members are progressively extruded or mushroomed each time the blowout preventer is closed. Thus, after only a few closing and opening sequences, the forward ends of these sealing members will be so permanently deformed that they will protrude slightly in front of the forward faces of the metal rams. Accordingly, when the blowout preventer is again closed in successive operations, once these unsupported forward ends of the sealing members contact one another around the interposed suspension member, a substantial pressure diiferential will tend to mushroom their abutting ends further and displace elastomeric material circumferentially and outwardly in between the forward faces of the rams. Once the elastomeric material has separated the opposed faces of the rams, the rams can, of course, no longer be tightly engaged with one another. Moreover, increasing the axial closing forces in an effort to tightly seat the rams will, by virtue of the somewhat fluid-like properties of elastomers, also act on the extruded elastomeric material between the rams and force them still further apart. It has been found, therefore, that to assure that a tight sealing engagement is made, these inner sealing members must be replaced after only a very few operations. Although the actual replacement expense involved is itself only incidental, the loss of time in replacing the sealing members as well as the potential hazards should a sealing member fail to seal properly during the course of a well-completion operation create quite major disadvantages.
Accordingly, it is an object of the present invention to provide new and improved blowout preventers that can be successively operated for a considerable period of time without unexpected or premature seal failures. This and other objects of the present invention are accomplished by arranging the inner sealing members in a blowout rpreventer to be relatively movable in both axial directions with respect to the rams and mechanically connecting the sealing members to either hydraulic or mechanical actuating means.
The novel features of the present invention are set forth with particularity in the appended claims. The operation together with further objects and advantages thereof, may best be understood by way of illustration and example of certain embodiments when taken in conjunction with the accompanying drawings, in which:
FIG. 1 depicts a blowout preventer of the present invention arranged with other well-servicing apparatus;
FIG. 2 is an enlarged elevational view in cross-section of a portion of the blowout preventer shown in FIG. 1;
FIG. 3 is an enlarged elevational view taken along the lines 33 shown in FIG. 2;
FIG. 4 is a view of one element of the apparatus shown in FIGS. 2 and 3; and
FIGS. 5 and 6 respectively show portions of the blowout preventer of the present invention as it is being closed and opened.
Turning now to FIG. 1, a preferred embodiment is shown of a blowout preventor 10 of the present invention as it appears when mounted on the upper end of a typical wellhead 11 projecting above the surface of the ground. Well-servicing apparatus 12, such as that shown in copending application Ser. No. 594,031, filed Nov. 14, 1966, is erected to top of the blowout preventer 10. The wellservicing apparatus 12 is comprised of an upright tubular riser 13 that is secured at its lower end to the blowout preventer and has its upper end connected to one leg of an inverted, generally U-shaped, enclosed sheave 14. The other leg of the enclosed sheave 14 dependently supports an enclosed cable-feeding device 15 which is in turn tandemly connected to the upper end of a typical lubricator 16. To maintain the apparatus 12 in its upright position, suitable supporting means, such as a truck-mounted erection device (not shown), are provided to support a cable 17 connected to the top of the enclosed sheave 14.
A suspension cable 18 spooled in the usual manner on a powered winch (not shown) to one side of the wellhead 11 is brought generally horizontally toward the wellhead and passed around the underside of a pulley 19 from whence it is directed upwardly into a stufiing box 20 on the lower end of the lubricator 16. After passing through the lubricator 16 and cable-feeding device 15, the cable 18 enters the enclosed sheave 14 where its direction is reversed to bring it downwardly into the upper end of the riser 13. The free end of the cable 18 is secured in the usual fashion to the upper end of a well instrument or tool 21 which, at the instance depicted in FIG. 1, is still confined in the riser 13 above the blowout preventer 10.
As is fully explained in the aforementioned copending application, the enclosed sheave 14 includes a plurality of longitudinally aligned pulleys or grooved rollers 22 that rotatably support the cable 18 to guide it through the sheave. By employing the enclosed sheave 14 the overall height of the well-servicing apparatus 12 is, of course, graetly reduced. Similarly, the cable-feeding device 15 is fully described in this copending application and, inasmuch as it also plays no particular part in the present invention, it is only necessary to mention that a smalldiameter, solid wire 23 is spooled from powered reels 24 and 25 at opposite ends of the device and passed over appropriately arranged idler pulleys 26 and 27 before entering the axial bore of the device. By frictionally engaging the small-diameter wire 23 against the suspension cable 18 and driving the reels 24 and 25, the cable is pulled through the lubricator 15 until the well tool 21 has reached a depth in the well bore where the combined weight of the tool and cable will carry the tool on downwardly against the opposing pressure forces acting on the cable.
Turning now to FIG. 2, a cross-sectional view is shown of a major portion of the blowout preventer 10 of the present invention. As seen there, the blowout preventer 10 is housed in a somewhat cross-shaped pressure housing 28 having a generally upright tubular section 29 that is mounted between the wellhead 11 and riser 13 and defines a continuous inner bore 30 which, preferably, corresponds to the internal diameter of the wellhead.
Inasmuch as the two halves of the blowout preventer 10 are identical with but one exception, the forthcoming description will be generally directed to a description of the elements in one half, with the same reference numbers being used for the corresponding elements in the other half. Later-a1 tubular branches 31 are provided on each side of the mid-portion of the upright housing section 29, with the respective bores 32 of each branch being diametrically opposed and coincidentally aligned with one another. Thick-walled tubular members or rams 33 are slidably mounted in the bores 32 of the branches 31 and have their upper surfaces fluidly sealed therein by specially fonmed, elastomeric sealing members 34. Cylindrical elastomeric sealing members 35 are slidably disposed in the tubular rams 33. To secure the rams 33 against rotation with respect to the branches 31, longitudinal keys 36 on the rams are respectively disposed in complementary grooves 37 running the full length of the bores 32. It will also be appreciated that the full-length key-ways 37 will also serve to equalize any pressure differential across the length of the rams 33 and inner sealing members 35 so that well pressure will be acting on their opposite ends to pressure-balance these elements.
Although the rams 33 could just as well be fluidly sealed around their full circumference, it is preferred to seal only the upper half of each. To accomplish this, the elastomeric sealing members 34 are arranged as best seen in FIGS. 2-4 to seal around only the upper circumferential half of the -mid-portion of the rams 33 as well as from there along a longitudinal path on each side of the rams to their forward faces. Accordingly, as best seen in FIG. 4, each sealing member 34 is comprised of a semi-circular section 38 having an elongated integral projection 39 extending perpendicularly from each of the free ends of this semi-circular section. The semicircular section 38 and longitudinal projections 39 are rectangular in crosssection and are received in complementary grooves formed in the outer surface of the rams 33 so that, when they are in place, the outer surfaces of the sealing members 34 will be flush with the outer surfaces of the rams.
Four inwardly directed integral radial projections 40 (only three seen in FIG. 4) are spaced around the inner surface of the semi-circular section 38 and adapted for reception in complementary radial bores in the rams 33 so that the free ends of these projections will be in contact with the contiguous outer surfaces of the inner sealing members 35. Similarly, the free ends of the longitudinal projections 39 are turned inwardly to provide projections 41 that are complementarily received in rectangular transverse grooves formed across the horizontal center lines of the forward faces of the rams 33. The inner ends of these projections 41 are also engaged with the contiguous outer surfaces of the inner sealing members 35. Thus, in view of the inherent property of elastomeric materials, inwardly directed axial forces on the rear of the inner sealing member 35 will be proportionally transmitted to the projections 40 and 41 to expand the semi-circular sections 38 and longitudinal projections 39 outwardly into sealing engagement with the inner bores 32 of the branches 31.
The forward faces of the rams 33 and inner sealing members 35 are respectively provided with semi-circular transverse grooves 42 (FIGS. 2 and 3) that extend along their common vertical axes and have a diameter substantially the same as that of the suspension cable 18. In this manner, whenever the blowout preventer 10 is closed, the suspension cable 18 will be snugly confined within the cylindrical bore defined by the opposed semi-circular grooves 42. To ensure that the opposed grooves 42 will mate as well as to vertically align the portions of the grooves in the sealing members 35 with those vertical groove portions in the rams 33, the inner sealing members are co-rotatively secured to the rams by means such as properly oriented longitudinal keys 43 on the sealing members that are received in complementary grooves formed in the inner bores 44 of the rams.
To ensure that the suspension cable 18 will enter the semi-circular grooves 42 as the blowout preventer 10 is closed, guide means such as arcuate plates 45 having V-shaped notches 46 in their forward ends are secured to the forward ends of each of the rams 33. The apexes of these notches 46 are, of course, accurately aligned with the semi-circular grooves 42. By mounting one of the guide plates 45 on the top of one of the rams 33 and the other guide plate on the bottom of the other ram, the free ends of the guide plates will be received in complementary recesses 47 formed in the corresponding surface of the opposite ram whenever the blowout preventer 10 is closed. In this manner, as the rams 33 are being brought together, the V-notches 46 in the guide plates 45 will centralize the suspension cable 18 at opposite ends of the semi-circular grooves 42 to properly guide the cable into position along the vertical center line of the upright housing section 29.
The rearward ends of the inner sealing members 35 are respectively reinforced by thick, rigid discs 48 which have a diameter substantially equal to that of the sealing members and are positively secured thereto by means such as axial studs 49 extending into the rear of each sealing member. The rearward end of the rams 33 are preferably extended beyond the rearward ends of the sealing members 35 and counterbored, as at 50, to provide rearwardly facing shoulders 51 at the junction of the counterbores and axial bores 44 as well as to receive the enlarged forward end or head portions 52 of tubular members 53 that are respectively coaxially disposed within the lateral housing branches 31 and extended therebeyond. The counterbores 50 are terminated so that the shoulders 51 will be even with the rear surfaces of the discs 48. A split ring 54 or the like fastener within the entrance of each of the counterbores 50 and just to the rear of the head portion 52 releasably confines it within the counterbore and holds the forward face of the head against the shoulder 51 and disc 48. Each rigid disc 48 is releasably secured, as by threads, to one end of an elongated, cylindrical rod 55 that is coaxially disposed and fluidly sealed in its associated tubular member 53 and extended on beyond its rearward end.
Accordingly, it will be appreciated that insofar as has been described, the rams 33 are moved laterally in either direction within their respective branches 31 by corresponding movements of the tubular actuating members 53. Similarly, since the enlarged heads 52 also engage the rear of the discs 48, the inner sealing members 35 will be simultaneously moved inward-1y along the rams 33 by inward movements of the tubular members 53. Although the inner sealing members 35 are purposely not secured within the rams 33, outward movement of the tubular actuating members 53 will tend to return the inner sealing members along with the rams by virtue of their frictional co-engagement. For reasons that will subsequently become apparent, however, it should be kept in mind that the cylindrical actuator rods 55 are positively connected (through the discs 48) to the inner sealing members 35 so that these rods can be pulled outwardly relative to the tubular actuator members 53 for moving the inner sealing members rearwardly and positively in relation to the rams 33.
To operate the rams 33 automatically, pneumatic or hydraulic means are provided such as annular pistons 56 connected to the rearward ends of the tubular actuator members 53. Each of these pistons 56 are slidably disposed and fluidly sealed in a piston cylinder 57 that is coincidentally aligned and releasably connected to the outer end of each of the lateral branches 31. Spaced lateral ports.58 and 59 in the piston cylinders 57 provide communications to the pressure-tight chambers 60 and 61 defined therein on opposite sides of the pistons 56. Thus, by appropriately connecting a suitable pneumatic or bydraulic source (not shown) by paralleled pressure lines 62 and 63 (FIG. 1) to the ports 58 and 59 (FIG. 2), the rams 33 can be automatically operated in unison. By admitting a suitable fluid under pressure into the rearward port 59 (and its counterpart in the other cylinder 57), the rams 33 will be moved in unison toward one another until their opposed faces come together in the middle of the pressure housing 28. Similarly, by applying pressure to the forward port 58 (and its counterpart in the other cylinder 57), the rams 33 will be simultaneously retracted and moved apart.
As already discussed, inward movement of the tubular members 53 will simultaneously move the rams 33 and their respective inner sealing members 35. However, to provide increased sealing force once the opposed faces of the rams 33 are engaged, a slidable piston 64 connected to the outer end of each of the actuating rods 55 is fluidly sealed within a counterbore 65 in the rearward face of each of the pistons 56. A lateral passage 66 through each of the tubular members 53 provides fluid communication between the forward pressure chamber 60 and the enclosed forward portion of the counterbore 65.
It will be appreciated, therefore, that the pressure in the rearward chambers 61 will be simultaneously effective on the rear faces of the pistons 56 and 64. Accordingly, whenever pressure is applied to the rearward hydraulic chambers 61, the pistons 56 and 64 will simultaneo'usly move forwardly until the opposed faces of the rams 33 engage. Then, any further increase in pressure in the chambers 61 will be effective to move only the inner pistons 64 further to urge the sealing members 35 forwardly in relation to the rams 33 and press the forward faces of the inner sealing members even more tightly against one another and around the suspension cable 18 to provide a more positive sealing engagement therewith.
Mechanical ram-actuating means are also provided by fluidly sealing and threadedly connecting tubular actuator members 67 in axial bores 68 through removable end walls 69 that close off the rear of the cylinders 57. These actuator members 67 are adapted for longitudinal travel into and out of the piston cylinders 57 by rotating operating handles 70 near the outer ends of the actuator members. The forward ends of the actuator members 67 are enlarged, as at 71, so that they will engage the rearward faces of both the outer pistons 56 and the inner piston 64 when the rams 33 are fully retracted. In this manner, by manually advancing the actuator members 67, the pistons 56 and 64 can be moved forwardly to close the rams 33 and inner sealing members 35 should the pressure-operated ram-actuating means not function.
It is of particular significance to the present invention that means are provided for independently retracting the inner sealing members 35 into the rams 33 either automatically or manually before the rams are reopened. To achieve this automatically, biasing means are provided such as springs 72 that are disposed in the counterbores and held in compression between the forward faces of the smaller pistons 64 and shoulders 73 defined by the bottoms of the counterbores within the piston members 56.
Accordingly, it will be appreciated that whenever pressure is applied to the rearward pressure chambers 61, the pistons 56 and 64 will move inwardly in unison. Then, as best seen in FIG. 5, once the rams 33 come together, continued pressure in the chambers 61 (suflicient to further compress the springs 72) will apply an increased axial load on each of the discs 48 at the rear of the sealing members 35. By virtue of the inherent pressure-transmitting properties of elastomeric materials, this increased axial loading will be transmitted in all directions through the sealing members 35 to tightly seal their opposed forward faces as well as to transmit radial forces through the projections 40 and 41 to tightly seal the outer sealing members 34 against the inner walls of the lateral branches 31.
To retract the rams 33 and sealing members 35 automatically, pressure is applied through the lines 63 to the forward chambers 60. It will be understood, however, that the pressure forces causing the inner pistons 64 to retract will be supplemented by the force of the springs 72. Thus, as best seen in FIG. 6, upon application of pressure in the forward chambers 60, the added force from the springs 72 will retract the inner sealing members 35 back into their associated bores 44 as the rams 33 are being opened. In this manner, the inner sealing members 35 will always be positively withdrawn into their associated bores 44 as the blowout preventer 10 is opened to ensure that the pressure differential acting across the housing 28 can not extrude the forward ends of the sealing members as has been the case heretofore with prior-art devices. In this manner, by ensuring that the sealing members 35 are fully supported within the rams 33 at all times, there can be no progressive mushrooming of the forward ends of the inner sealing members.
Manual actuation of the inner sealing members 35 is accomplished by engaging the forward end 74 of a cylindrical actuator rod 75 with the outer face of each of the inner pistons 64 and fluidly sealing this rod within each of the tubular actuators 67. An operating wheel '76 is secured to a nut 77 threadedly connected to threads 78 on the outer ends of each actuator rod 75 for actuating the rods independently of the tubular actuators 67. It will be appreciated, of course, that the actuator rods 75 can also be manually tightened should it be necessary to develop increased axial liading on the sealing members 35 in lieu of applying increased hydraulic pressure in the chambers 61.
It will be realized, of course, that it is preferable to automatically operate the blowout preventer 10. On occasion, however, it may be necessary to operate the blowout preventer 10 manually. To do this, the piston cylinders 57 are removed from the branches 31 and the actuators 53 and 54 disconnected from the rams 33 and sealing members 35 respectively. By making the enlarged heads 71 similar or identical to the enlarged heads 52, the actuators 67 can be secured to the rams 33. Similarly, the forward ends 74 of the actuators 75 are counterbored and threaded, as at 79, for connection to the discs 48. Once the actuators 67 and 75 are connected, the end walls 69 are threadedly connected by threads 80 to the branches 31.
Once the manual actuating means are connected, the blowout preventer 10 can be operated. By tightening the actuators 67, the rams 33 and inner sealing members 35 are closed together. Then, once the forward faces of the rams 33 come together, the actuator 75 is tightened further to ensure that the forward faces of the inner sealing members 35 are tightly sealed around the suspension member 18. To open the blowout preventer 10, the ac tuator 75 is retracted first to pull the inner sealing members 35 back into their bores 44. Then, once the inner sealing members 35 are retracted, the rams 33 are opened with the actuators 67.
Accordingly, it will be appreciated that the present invention has provided means by which it is now possible to positively retract the inner sealing members of blowout preventers to prevent their outward extrusion which, in time, would otherwise interfere with, if not completely defeat, the successful operation of the blowout preventers. By assuring that the elastomeric inner sealing members are fully supported at all times, the tendency of the elastomeric material to extrude is greatly reduced if not totally eliminated. Moreover, even should some extrusion occur, by mechanically connecting the individual actuating members to the rear of the inner sealing members, the sealing members can be positively retracted relative to the rams to compensate for any permanent deformation of the elastomeric material. It will, therefore, be appreciated that blowout preventers arranged in accordance with the present invention will provide extended, trouble-free operation that has not heretofore been possible.
While a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.
What is claimed is:
1. A blowout preventer adapted for sealing around a suspension member emerging from a well conduit and comprising: a pressure housing adapted for connection to a well conduit and having a central opening therethrough sized and arranged to receive a suspension member; first closure means on one side of said housing and adapted for sealing engagement with one side of a suspension member in said central opening; second closure means on the opposite side of said housing and adapted for movement laterally into engagement with the other side of a suspension member in said central opening, said second closure means including a rigid tubular member and an elastomeric sealing member movably disposed and fluidly sealed therein, the forward end of said sealing member being adapted to sealingly engage that other side of a suspension member; first actuating means for moving said second closure means into and out of sealing engagement with that other side of a suspension member; and second actuating means for retracting said sealing member into said tubular member.
2. The blowout preventer of claim 1 wherein said first actuating means are pressure-operated and said second actuating means include spring means normally urging said sealing member into said tubular member.
3. The blowout preventer of claim 1 wherein said first actuating means include a first actuating member adapted for engagement against the rearward ends of said tubular member and said sealing member for moving said second closure means forwardly into said central opening, and means connecting said first actuating member to said tubular member for moving said tubular member rearwardly out of said central opening; and said second actuating means include a second actuating member connected to said sealing member and movable independently of said first actuating member.
4. The blowout preventer of claim 3 further including first and second piston means respectively connected to said first and second actuator members, cylinder means for receiving said piston means and adapted for selectively applying pressure to the opposite sides of said piston means, and spring means normally urging said second actuator member rearwardly in relation to said first actuator member.
5. The blowout preventer of claim 4 further including means for selectively moving said sealing member forwardly in relation to said tubular member independently of forward movement of said first actuating member.
6. A blowout preventer adapted for sealing around a suspension member emerging from a well conduit and comprising: a pressure housing having a central portion with an opening therethrough sized and arranged to re ceive a suspension member and opposed tubular branch portions on opposite sides of said central portion; first and second closure means respectively disposed in said branch portions and adapted for movement therein into and out of engagement with the opposite sides of a sus pension member in said central opening, each of said closure means including a rigid tubular member and a cylindrical elastomeric sealing member slidably disposed and fluidly sealed therein, the forward ends of said sealing members being adapted to sealingly engage one another and the opposite sides of a suspension member; first actuating means for moving said closure means into and out of sealing engagement with one another and a suspension member including a tubular first actuating member in each of said branch portions and having a forward end adapted for engagement against the rearward ends of its associated tubular member and sealing member for moving its associated closure means forwardly into said central opening, and means connecting the forward ends of each of said first actuating members to its associated tubular member for moving said tubular members rearwardly out of said central opening; and second actuating means for retracting said sealing members into said tubular members including a cylindrical second actuating member movably disposed through each of said first actuating members and having a forward end connected to its associated sealing member.
7. The blowout preventer of claim 6 further including first and second manual actuators respectively connected to the rearward ends of each of said first and second actuator members; means interconnecting said first and second actuator members for movement of said second actuator members relative to said first actuator members and independent of movement of said first actuator members; and means interconnecting said first actuator members to said housing for moving said first and second actuator members together whenever said first actuator is moved.
8. The blowout preventer of claim 6 further including first and second piston members respectively connected to the rearward ends of each of said first and second actuator members; first and second cylinder means for respectively receiving said piston members and adapted for selectively applying pressure to the opposite sides of said piston members; and spring means between each associated pair of said piston members normally urging each of said second actuator members rearwardly in relation to its associated first actuator member.
9. The blowout preventer of claim 8 further including third actuator members for selectively moving each of said second actuator members forwardly in relation to its associated first actuator member.
10. The blowout preventer of claim 8 wherein said second cylinder means are formed in the rearward ends of its associate first piston member.
References Cited UNITED STATES PATENTS 2,690,320 9/1954 Shalfer et al 25l1 2,855,172 10/1958 Jones 251l 3,036,807 5/1962 Lucky et al 25 l1 X 3,102,709 9/1963 Allen 251l 3,132,662 5/1964 Allen 25l1 X STANLEY N. GILREATH, Primary Examiner.
US Cl. X.R. 16675