GB2169063A - Fail safe gate valves and actuators therefor - Google Patents

Abstract

In a fail safe gate valve comprising a reciprocable valve stem 28, pistons 82 offset from the stem axis are movable within cylinders 83 by supply of operating fluid to move a stem flange 80 (and thus the gate member) in one direction, the flange being moved up an exhaust of operating fluid in the other direction by a spring 35 compressed between the flange 80 and the valve bonnet. <IMAGE>

Description

GB2169063A 1

SPECIFICATION

Fail safe gate valves and actuators therefor 5 This invention relates to a fail safe gate valve and an actuator for such a valve. The present invention is particularly concerned with a structure by which the valve or actuator is responsive to an operating fluid to control the 10 gate.

The invention finds use in fail safe gate valves and actuators therefore wherein the gate is moved to and maintained in one posi tion under one or more controlled conditions, 15 such as a predetermined fluid pressure level, and yieldably urged to its other position, upon one such condition failing or otherwise not be ing maintained, or in response to a control signal.,Further discussion of the operation of 20 fail safe gate valves may be found in our co pending application 8301744 (Serial No.

2115111) from which the present application is divided.

The invention will be described in terms of 25 the use just-mentioned and of valves and ac tuators in which the gate may be moved to the one position above-mentioned by means of a handwheel.

As above indicated the present invention is 30 concerned with means by which a fail safe gate valve or actuator therefor is responsive to an operating fluid to control the gate.

According to one aspect of the present in vention there is provided a fail safe gate 35 valve, comprising a valve body having a flowway therethrough, a gate member mov able within the valve body between positions opening and closing the flowway, a generally cylindrical housing on the valve body, a stem 40 on the gate member extending from th body 105 and into the housing for longitudinal reciproca tion therein, a flange on the stem, a plurality of cylinders mounted on the outer end of the housing each to one side of the stem axis, a 45 respective piston sealably reciprocable with respect to each cylinder and extending into the cylinder for engaging the stem flange in order to move the closure member to one position in response to the supply of operating fluid to 50 the cylinder, and spring means within the housing and compressed between the stem and the inner end of the housing to move the closure member to its other position upon the exhaust of operating fluid from the cylinder, 55 said pistons and outer end of the stem being 120 generally in side-by-side relation with the cylin ders in said other position of the closure member.

Preferably the housing of the above-defined 60 valve has an inner end wall through which the 125 stem sealably extends, and the cylinders ex tend outwardly from the outer end wall laterally to one side of the stem.

According to a further aspect of the inven 65 tion there is provided a fail safe gate valve 130 actuator, comprising a generally cylindrical bonnet adapted to be mounted on the body of a valve, a stem adapted to be connected to a gate member mounted in the valve body 70 for movement between positions opening and closing a flowway through the body, means mounting the stem within the bonnet for longitudinal reciprocation therein in opposite directions in order to move the closure member between said positions, a flange on the stem, a plurality of cylinders mounted on the outer end of the bonnet each to one side of the stem axis, a respective piston sealably reciprocable with respect to each cylinder and extending into the cylinder for engaging the stem flange in order to move the gate member to one position in response to the supply of operating fluid to the cylinder, and spring means within the bonnet and compressed be- 85 tween the stem and the inner end of the bonnet to move the closure member to its other position upon the exhaust of operating fluid from the cylinder, said pisto ns and outer end of the stem being generally in sideby-side re- 90 lation with the cylinders in said other position of the closure member.

Preferably the bonnet of the above-defined actuator has an end wall through which the stem is sealably extendable, and the cylinders 95 extend outwardly from the outer end wall laterally to one side of the stem.

In both the valve and the actuator it is preferred that the spring means surrounds the stem and is compressed between the flange 100 and the inner end of the housing or bonnet.

The invention will be further described with reference to the accompanying drawings in which Figs. 1 to 11 illustrate a valve structure, not itself embodying the invention, and a modification of which structure in accord with the invention is shown in Fig. 12. The description of Figs. 1 to 11 will serve to disclose various detail features of the construction, that of Fig. 12 concentrating on the modification in which the invention is embodied.

In the drawings, wherein like reference characters are used throughout to designate like parts:

Figure 1 is a side view of the one embodi- 115 ment of a fail safe valve wherein the control fluid pressure is pneumatic, the left hand side of the valve being in elevation and the right hand side being in vertical cross section to illustrate the gate moved to its upper, closed position upon removal of control fluid pressure to which the means for moving the stem is responsive; Figure 2 is an enlarged vertical sectional view of the actuator of the valve of Fig. 1, with the stem thereof. raised following closing of the gate, and the handwheel lowered to engage with the nut for manually rotating the stem, whereby the valve may be returned to open position by rotation of the handwheel, and also showing a flag rotated to a raised GB2169063A 2 position to indicate lowering of the handwheel; ' Figure 3 is a vertical sectional view of one side of the actuator of Figs. 1 and 2, similar to Fig. 2, but upon the supply of control fluid pressure to the pressure chamber of the actuator to raise and thereby disengage the handwheel from the nut and maintain the stem in its lower position to hold the valve open, 10 and thus restore the system to pressure control responsive condition, and also showing the flag released by lifting of the handwheel to rotate to a lowered position to indicate raising of the handwheel; Figure 4 is a horizontal sectional view of the upper end of the valve of Fig. 1, as seen along broken lines 4-4 thereof; Figure 5 is a cross-sectional view of the actuator, looking downwardly from broken 20 lines 5-5 of Fig. 3; Figure 6 is another cross-sectional view of the actuator, looking up from broken line 6-6, of Fig. 3; Figure 7 is a vertical sectional view of a 25 portion of the actuator, as seen along broken lines 7-7 of Fig. 3, to show the lower end of the pawl raised from rotative engagement with the nut; Figure 8 is another cross-sectional view of 30 the actuator of Figs. 1 to 7, as seen along broken lines 8-8 of Fig. 7, to show brake shoes carried by the nut for engagement with the bonnet to retard upward movement of the stem upon lifting of the handwheel to the di- 35 sengaged position of Fig. 3, Figure 9 is another vertical sectional view of the upper end of the actuator of Figs. 1 to 7, to show the mechanism for lifting the handwheel from engaged position with respect 40 to the nut automatically in response to a predetermined environmental temperature condition; Figure 10 is another view of the upper end of the actuator of Figs. 1 to 7, broken away 45 in part to show the mechanism shown in Fig.

9 from the left hand side thereof; Figure 11 is a view of the upper end of such actuator, as shown along broken lines 11-11 of Fig. 9; and 50 Figure 12 is a side view of the fail safe 115 valve constructed in accordance with the pre sent invention, in which the control fluid is hydraulic, with the right hand side thereof and the upper end of the left hand side being 55 shown in section.

With reference now to the above-described drawings, the valve 20 shown in Fig. 1 includes a valve body 21 having a flowway 22 therethrough and flanges on its opposite ends 60 to enable the valve to be connected in a pipeline with its flowway aligned with the axis of the pipeline. A gate 23 mounted for vertical reciprocation within the cavity of the valve body has a port 24 therethrough which is 65 raised above the flowway, in the closed posi- tion of Fig. 1, and aligned with the flowway, in the open position (not shown).

An actuator 25 for moving the gate between its opened and closed positions in- 70 cludes a bonnet 26 adapted to be mounted on the valve body and having a lower end wall 27 for closing the upper end of the body cavity when the -bonnet is mounted thereon. A stem 28 is mounted for reciprocation within 75 the bonnet 26 and has a lower end which extends sealably through a hole 29 in the bonnet end wall 27 for releasable connection with the upper end of the gate. As shown, this connection comprises a "T" on the lower 80 end of the stem 28 which fits within a correspondingly shaped slot in the upper end of the gate.

The bonnet 26 includes a cylindrical housing 30 having a depending, outer annular portion 85 30A which has threads 31 about its inner diameter for connection with threads about an upstanding portion of the valve body to connect the housing and the valve body. An inwardly turned flange on the upper end of 90 housing portion 30A bears upon an upwardly facing shoulder on the end wall 27 of the bonnet to hold the wall tightly against the upper end of the neck of the upper end of the valve body when the housing 30 is threadedly 95 connected thereto.

A flange 33 is fixedly connected to the stem 28 for reciprocation therewith the housing, and is urged toward an upper position in which a shoulder 28C thereon engages a 100 shoulder on wall 27 beneath hole 29 by means of a coil spring 35 acting between the flange and the lower end of the depending portion 30A of the housing. More particularly, in the pneumatic embodiment of the fail safe 105 valve of Figs. 1 to 11, the outer circumference of the flange extends close to inner circumference of housing 30 and carries a seal ring thereabout for slidably sealing within the housing. Thus, flange 33 serves as a piston 110 which, as will be described, is adapted to be urged downwardly by control fluid in opposition to the upward force due to spring 35 and line pressure within the valve body acting over the area of stem 28 slidable within hole 29. The lower end of the depending annular portion 30A of the housing is ported at 36 to vent the housing beneath the piston.

As will be described in detail to follow, an upward extension 39 of the bonnet above the 120 housing 30 is enclosed or sealed off so as to form with the housing above the piston flange 33 a variable volume pressure chamber for the control fluid. A pipe 37 connects with a port 38 in the upper end wall 34 of the bonnet 125 housing to permit control pressure to be supplied to or removed from this chamber, and in use of the valve in a system of the type contemplated by the present invention, this control fluid will provide sufficient force to over- 130 come that of the spring 35 and line press to GB2169063A 3 maintain the piston and stem 28 in their lowered positions (Fig. 3) and thus hold the gate in its open position. As previously described, upon removal of the control pressure from the 5 pressure chamber, the forces due spring 35 and line pressure lift the piston and the stem back to the positions of Fig. 1 to close the gate. However, upon removal of the control fluid, the spring is capable of closing the gate, 10 even in the absence of pressure in the line.

The bonnet extension comprises a tubular body 40 which is of considerably less diameter than the bonnet housing 30 and which has a lower end threadedly received within a 15 central opening 34A in the top end wall 34 of the housing. The axis of the extension is aligned with the housing so as to receive the upper end portion of the stem centrally thereof. As best shown in Fig. 3, a handwheel 20 41 is mounted for rotation on the upper end of housing extension 39 by means of a shaft 42 which depends from the center of the handwheel for rotation within an opening 43 in the upper end of the tubular housing 40.

25 More particularly, and as will be described, the shaft is reciprocable coaxially of stem 28 between an upper position (Fig. 3) disengaged from the stem, and a lower position (Fig. 2) in which it is rotatively connected to the stem.

30 The shaft is rotatable and reciprocable within an O-ring 44 within the opening 43 so as to sealably enclose the upper end of the housing extension, and, thus with the housing above piston flange 33, provides a piston which, 35 with piston 33, defines the pressure chamber within the bonnet with which control line port 38 connects.

A nut 45 is mounted for rotation within the bonnet extension beneath the lower end of 40 handwheel shaft 42. More particularly, the nut is of a ball type having a ring 45A at its upper end which is fixed against axial movement by a lower bearing on the upper end of a sleeve 46 supported within the bonnet ex- 45 tension by means of a snap ring 47, and an upper bearing which is held beneath a downwardly facing shoulder 48 on the reduced diameter portion of the upper end of the bonnet extension. As shown in the drawings, the nut 50 45 also includes a ball race housing 45B depending from the ring 45A, and the upper end portion of the stem 28 extends upwardly through the inner diameter of the ball nut and into the lower hollow end of the handwheel 55 shaft 42. As shown, the balls within the ball race housing engage with matching grooves on the upper end portion of the stem so that, as the nut is rotated in a clockwise direction (looking down), the stem is caused to move 60 downwardly and thus lower the gate to its open position.

As best shown in Fig. 5, the upper end of the support ring of the nut 45 has circumferentially spaced slots beneath the lower end of 65 the shaft 42. As best shown in Fig. 6, the lower end of the shaft 42 has circurnferentially spaced teeth 47 adapted to fit within the slots 46 when the handwheel and thus its shaft are lowered to position of Fig. 2, so as 70 to rotatably connect the shaft and nut. When the handwheel is raised to move the lower end of its shaft out of and into rotative connection with the nut, a shoulder 48 about the shaft engages a downwardly facing shoulder 49 in the housing beneath opening 43 to prevent removal of the handwheel.

The handwheel and thus its shaft are located in the upper position by means of spring-pressed ball detents 50 which are car- 80 ried by the bonnet extension and movable, when the shaft is raised, into a lower annular groove 51 thereabout. Another annular groove 52 is formed about the shaft above the groove 51 so as to receive the ball detents 85 50 when the handwheel and shaft are lowered from the upper position to the lower position of Fig. 2.

As well known in the art, because of its mechanical efficiency, a ball nut lowers the 90 power requirements in operating the handwheel to lower the stem, as compared with more conventional jack screw arrangements. In fact, if the handwheel were raised from the position of Fig. 2 to the postion of 95 Fig. 3 so as to disconnect the shaft from the nut, the force of the spring 35 and the force due to line fluid acting over the cross-sectional area of the stem extendible through hole 29 would allow the gate to rise from its open 100 position to its closed position.

When the shaft on the handwheel is lowered to rotatably engage the nut, the nut is held against retrograde movement-i.e., in a counterclockwise direction looking downwardly 105 on the nut-by means of a pawl 50 having a ratchet tooth 51 on its lower end and carried within a bore 52 in the upper reduced diameter portion of the bonnet extension (see Fig. 6) for movement vertically into and out of 110 engagement with one of the slots 46 on the top side of the nut. As shown in Fig. 7, the front side of the ratchet tooth 51 is formed with a vertical face 51A, while the back side thereof is tapered at 51B so that, when the 115 pawl is lowered with the handwheel shaft 42, as will be described below, its face 51A will engage one side of the slot in the nut to prevent retrograde movement of the nut, while its tapered face will be free to ride up and 120 over the other side of the slot upon clockwise rotation of the nut with the handwheel shaft. The pawl is urged downwardly to its lower position by mean of a coil spring 53 acting between its upper end and the top wall of the 125 bonnet extension, and a flange 54 on the upper end of the pawl is supported on an upwardly facing shoulder 55 about the handwheel shaft so that the pawl will move downwardly and upwardly with the shaft, as 130 the shaft is shifted by the handwheel, but, GB2169063A 4 when lowered, will rise and fall as it ratchets over the nut.

Following clockwise handwheel rotation to rotate the nut and lower the stem and thereby 5 open,the valve, the handwheel may be raised to disengage it from the nut. Since the pawl is also lifted therefrom, the nut is free to move in a counterclockwise direction, and, due to the mechanical efficiency of the ball 10 nut, the force due to the coil spring 35 as well as line pressure acting upon the stem 28 will cause the stem to rise, and the nut to counter rotate in order to lift the gate to closed position. Brake shoes 56 are carried 15 within an annular groove 57 about the support ring of the nut to frictionally engage the inner diameter of the bonnet extension, as best shown in Fig. 8, in order to retard the counterclockwise rotation of the handwheel as the 20 stem is being raised, and thus reduce the impact of shoulder 28C on the stem with the shoulder on bonnet wall 27 beneath hole 29.

As previously described, and as will be apparent from the foregoing description, the ex-

25 tension of shaft 42 sealably within O-ring 44 of the housing extension of the bonnet provides a piston which is urged upwardly to disengage the shaft from the nut by the supply of control fluid to the pressure chamber of 30 the bonnet. For example, with reference to Fig. 2, with th e stem raised to close the valve, as may have occured due to removal of control fluid, the system may be returned to a control fluid responsive condition by the sup- 35 ply of control fluid to the pressure chamber, which move the piston flange 33 downwardly to return the gate to open position. At the same time, control fluid acts upon the piston area of the shaft 42 so as to raise the shaft 40 and handwheel, and thus disengage its teeth and the pawl from the nut. Consequently, as long as control fluid remains in the pressure chamber of the housing, the handwheel is positively held out of rotative engagement 45 with the nut, thereby preventing the inadvertent manual manipulation of the handwheel. More particularly, the handwheel will remain in its upper position, even following removal of control fluid, and thus closure of the valve, until manually pushed downwardly to its nut 115 engaging position.

Stem 28 is preferably comprised of axially extendible and contractible upper and lower ends 28A and 28B, respectively. As shown, 55 the upper end is threadedly connected to the nut, and the lower end is fixed to piston flange 33 and extends sealably through the hole 29 for connection with the gate. More particularly, the upper and lower ends of the 60 stem are connected for rotation with one another by means of a spline 57 formed on the lower portion of the upper end of the stem which is received within a hollow upper portion of the lower end 28B, and a pin 58 65 on the upper portion of the lower end 28B of the stem for sliding vertically within the spline 57. As shown in Fig. 2, as the upper and lower ends of the spline move into retracted position, pin 58 moves out of the spline 57, 70 and the upper and lower ends of the stem are maintained in rotative engagement with one another by means of a dog 59 on the upper end which moves into a slot 60 in the lower end of the stem. Thus, as shown, the upper 75 end of the stem is made up of an upper, relatively large portion which has pin 59 formed thereon, and a lower, relatively small portion which has the spline 57 formed therein. Consequently, when the upper and 80 lower ends of the stem are in their fully re- tracted position, torque is transmitted directly from the larger upper portion directly to the lower end, rather than through the lower smal ler portion in which the spline 57 is formed.

85 As will be understood, this two-piece stem enables the lower end of the stem to rise and fall with piston 33 to lift and lower the gate without rotating the nut, and thus eliminates unnecessary wear on the nut. Even if the up- 90 per end of the stem is partially lowered within the nut, from the position of Fig. 2 to the position of Fig. 3, this two-piece stem construction will reduce to at least some extent the need for rotating the nut as the lower end 95 of the stem is lifted its full stroke to raise the gate from its open to its closed position.

Piston flange 33 is of special construction to accommodate for eccentricity between the axis of the stem and the inner circumference 100 of the cylinder in the bonnet in which the piston is sealably slidable. Thus, the flange includes an inner disc 33A carried by the lower end 28B of the stem, and an outer disc 33B which carries an O-ring 33C in a groove 105 about its outer circumference for sealably sliding within the cylinder. More particularly, the outer disc has an inner circumference somewhat larger than the outer circumference of the inner disc so as to overlap therewith and 110 permit limited radial sliding of the outer disc with respect to the inner disc. The inner diameter of the inner disc is sealed with respect to the lower end of the stem by means of an O-ring 61 carried by the stem, and the inner and outer discs are sealed with respect to one another by means of an O-ring 62 carried within a groove in the upper face of inner disc 33 to form a sliding sea[ with respect to an overlapping, opposed lower face of the outer 120 disc 33B. Inner disc 33 is held down on a shoulder 63 about the lower end of the stem, and outer disc 33B is held downwardly upon the inner disc 33A, by means of a nut 64 threadedly engaged with the upper end of the 125 lower end of the stem. The nut 64 is of course made up with the stem only to the extent necessary to retain the piston flange on the stem, without interfering with radial movement of the outer disc of the piston flange 130 with respect to the inner disc thereof.

GB 2 169 063 A 5 is releasably secured As also previously described, a flag 65 is mounted oil the actuator bonnet for rotating between an outer, raised position with respect to the bonnet, so as to indicate that the 5 handwheel has been lowered into rotative engagement with the nut, and an inner position lowered along the side of the housing extension, as indicated in broken lines in Figs. 1 and 3, to indicate that the handwheel is raised 10 out of rotative engagement therewith. Thus, the flag is carried on the outer end of arm 66 which is pivotally connected to a member 67 extending upwardly from the upper end of the housing extension to one side thereof. More 15 particularly, the inner end of the arm is pivotally connected to member 67 by means of a pin 68 to permit it to swing from a generally horizontal position in which it raises the flag 65 to its handwheel lower indicating position, 20 and a depending position in which it lowers the flag to indicate that the handwheel is out of rotative engagement with the nut.

As will be appreciated, the arm and flag normally assume the depending position. How- ever, they are moved to their outwardly extended positions by means of a finger 69 extending from arm 66 at a right angle with respect to the arm 66 beneath a mounting ring 70 at the center of the handwheel which over the upper end of the stem. Thus, as the handwheel is lowered, the lower end of mounting ring 70 engages finger 69 to swing it downwardly to a position in which the arm 66 is swung outwardly 35 to its generally horizontal position. The flag is 100 held in its outwardly extending position by en gagement of the outer diameter of the mount ing ring 70 with the inner side of the finger 69 when it has been swung downwardly, as 40 best shown in Fig. 2.

The means by which the handwheel is auto- matically moved to its upper position in re sponse to a predetermined high temperature environment about the valve is shown in Figs.

45 9 to 11 to comprise a rod 71 which is verti cally reciprocable within a cylindrical opening 72 formed in the upper end of the housing extension beneath the mounting ring 70 of the handwheel. More particularly, the upper en 50 larged end of the rod 71 is guidably sliding 115 within opening 72 between the lower position shown in Figs. 9 and 10, and an upper posi tion in which the upper end of the rod moves out of the opening 72 to engage and lift the 55 mounting ring 70 of the handwheel to its upper position. Thus, the rod is yieldably urged toward its upper position by means of a coil spring 73 received about its reduced diameter lower end and acting between the enlarged 60 diameter upper end thereof and the lower end of opening 72.

The rod is held in its withdrawn position of Figs. 9 and 10 by means of a wire rod 74 releasably held across the opening 72 to bear 65 upon the upper enlarged end of the rod 7 1.

One end 75 of the wire rod is received in a hole in one side of a slot 76 in the housing extension so as to form a pivot about which the wire rod may swing in a counterclockwise 70 direction as indicated by the arrow of Fig. 10 to release the rod 71 for upward movement to lift the handwheel. The opposite end of the wire rod is normally held by means of a heat fusible element 77 supported by a bracket 78 75 fixed to a cutout recess 79 in a side of a housing extension. As shown, the upper end of retainer piece 77 is disposed over the free end of the wire rod 74 so as to hold the wire rod in its generally horizontal position until ele- 80 ment 77 fuses in the presence of the high temperature environment. Of course, when this occurs and the handwheel is lifted to disconnect from the nut, the nut is free to rotate so that the stem may be raised by the spring 85 35 and the force of line fluid in order to per mit the gate to fail closed.

Turning now to Fig. 12, it shows a fail safe valve that is substantially identical to the embodiment above described except in the construction of the mechanism which is responsive to supply of control fluid in order to normally maintain the valve in its open position and then permit it to fail close upon removal of control line fluid. This mechanism embody- 95 ing the present invention will now be de scribed.

A flange 80 is fixed to the lower end 28B of the stem by means of a nut 81 and is urged upwardly by means of a coil spring 35 mounted within the bonnet as described in connection with the hydraulic embodiment. However, in this hydraulic embodiment, the flange and thus the stem are urged downwardly by a series of pistons 82 reciprocable 105 within cylinders formed within tubular bodies 83 mounted on the upper wall 34 of the bonnet housing in circumferentially spaced-apart relation about the housing extension. Thus, the flange 80 terminates short of the inner 110 circumference of the bonnet housing so as to avoid contact therewith as it is reciprocated within the bonnet housing in response to the supply and removal of control fluid to and from the cylinders within tubular bodies 83.

The upper end of each of the pistons 82 carries an 0-ring 84 thereabout for sealably sliding within its cylinder, and is of such length as to cause its lower end to bear upon the upper side of flange 80 and move the 120 flange to its lowermost position to retain the valve in open position in response to the supply of control fluid. Control fluid is supplied to and removed from each of the cylinders through a common line 85 leading from a 125 source of hydraulic fluid and having branch lines leading to ports 86 in the upper ends of the cylinders.

Thus, although the shaft 42 on the handwheel is shown to be sealably received in 130 the opening 43 in the upper end of the hous- GB2169063A 6 ing extension, this is primarily for the purpose of preventing debris fromaccess to the ball nut and its associated parts. That is, there is no need fo the containment of pressure within a chamber formed within the bonnet housing.

Instead, the means by which the handwheel is automatically moved from its lower to its up per position in response to the supply of con trol fluid to the cylinders for pistons 82 corn 10 prises one or more pistons 90 slidable within 75 cylinders 91 formed in the upper end of the housing extension beneath the mounting ring of the handwheel. Rods 92 on these pistons extend sealably through bearings 93 so as to engage with the lower side of the mounting ring of the handwheel. As will be understood from Fig. 12, in the lower position of the piston 90, rod 92 is lowered to a position in which it does not interfere with downward 20 movement of the mounting ring with the handwheel. On the other hand, upon upward movement of the piston 90 to the position shown in Fig. 12, the upper end of the rod 92 engages the mounting ring to force the handwheel to its raised position. Control fluid 90 from a source common to that supplied to cylinders 83 is supplied to the lower end of piston 90 by means of line 94 branching from line 85 and leading to the lower end of the 30 cylinder 91. Consequently, and as above de scribed, as control fluid is supplied to each of the pistons 82 for maintaining the gate in its open position, the handwheel is automatically lifted to its upper position to disengage its 35 shaft 42 from the nut by which the stem is manually actuated.

It will be understood that the valve actuator of Fig. 12 is otherwise identical to that of Figs. 1 to 11. Thus, as indicated in Fig. 12, 40 an arm may be mounted on the housing ex tension to support a flag 65. Also, although not shown in Fig. 12, it will be understood that the valve actuator includes a paw[ of the construction and adapted to function in the manner of the paw] 50 described in connec tion with the pneumatic embodiment of Figs.

1 to 11. Additionally, of course, it may be provided with means such as that shown in Fig. 9, for causing the gate to fail closed re 50 sponsive to a predetermined environmental temperature condition.

Fail safe gate valves and actuators having a response to a predetermined environmental condition are the subject of our copending ap- plication 8506980 (Serial No. 2,155,595) also divided out of application 8301744.

Claims (7)

1. A fail safe gate valve, comprising a 60 valve body having a flowway therethrough, a 125 gate member movable within the valve body between positions opening and closing the flowway, a generally cylindrical housing on the valve body, a stem on the gate member ex tending from the body and into the housing for longitudinal reciprocation therein, a flange on the stem, a plurality of cylinders mounted on the outer end of the housing each to one side of the stem axis, a respective piston 70 sealably reciprocable with respect to each cylinder and extending into the cylinder for engaging the stem flange in order to move the closure member to one position in response to the supply of operating fluid to the cylinder, and spring means within the housing and compressed between the stem and the inne r end of the housing to move the closure member to its other position upon the exhaust of operating fluid from the cylinder, said pistons 80 and outer end of the stem being generally in side-by-side relation with the cylinders in said other position of the closure member.

2. A valve as claimed in Claim 1, wherein the housing has an inner end wall through 85 which the stem sealably extends, and the cylinders extend outwardly from the outer end wall laterally to one side of the stem.

3. A valve as claimed in Claim 1 or 2, wherein the spring means surrounds the stem and is compressed between the flange and inner end of the housing.

4. A fail safe gate valve actuator, compris-, ing a generally cylindrical bonnet adapted to be mounted on the body of a valve, a stem 95 adapted to be connected to a gate member mounted in the valve body for movement between positions opening and closing a flowway through the body, means mounting the stem within the bonnet for longitudinal re- 100 ciprocation therein in opposite directions in order to move the closure member between said positions, a flange on the stem, a plurality of cylinders mounted on the outer end of the bonnet each to one side of the stem axis, 105 a respective piston sealably reciprocable with respect to each cylinder and extending into the cylinder for engaging the stem flange in order to move the gate member to one position in response to the supply of operating 110 fluid to the cylinder, and spring means within the bonnet and compressed between the stem and the inner end of the bonnet to move the closure member to its other position upon the exhaust of operating fluid from the cylinder, 115 said pistons and outer end of the stem being generally in side-by- side relation with the cylinders in said other position of the closure member.

5. An actuator as claimed in Claim 4, 120 wherein the bonnet has an end wall through which the stem is sealably extendable, and the cylinders extend outwardly from the outer end wall laterally to one side of the stem.

6. An actuator as claimed in Claim 4 or 5 wherein the spring means surrounds the stem and is compressed between the flange and the inner end of the bonnet.

7. A fail safe valve or an actuator therefor, substantially as hereinbefore described with 130 reference to Fig. 12 of the accompanying 7 GB 2 169 063A 7 drawings.

Printed in the United Kingdom for ir Her Majesty's Stationery Office, Dd 8818935, 1986, 4235. Published at The Patent Office, 25 Southampton Buildings, London, WC2A 'I AY, from which copies may be obtained.