WO2007012136A1

WO2007012136A1 - Valve grinding

Info

Publication number: WO2007012136A1
Application number: PCT/AU2006/001062
Authority: WO
Inventors: Wayne Arthur Leonard; Geoffrey Laurence Winton; Kim Hua Goh; Ramon Keith Horton
Original assignee: Alcoa Of Australia Limited
Priority date: 2005-07-28
Filing date: 2006-07-28
Publication date: 2007-02-01
Also published as: RU2008105659A; CA2616148A1; BRPI0615982A2; CN101233352A

Abstract

Apparatus (10) for use with a valve (11) to perform a grinding operation on the valve. The valve (11) has a valve body (13) defining a valve seat (19) and a valve member (21) moveable into and out of engagement with the valve seat (19). The valve member (21) comprises a valve disc (25) and a valve stem (23). The valve (11) also has a bush (29) through which the valve stem (23) extends in threaded engagement therewith whereby relative rotation between the bush (29) and the valve stem (23) causes axial displacement of the valve stem (23) relative to the bush (29). The apparatus (10) comprises a drive transmission means (55) for providing a driving connection to the bush (29) and the valve stem (23). The drive transmission means (55) has first and second modes of operation, wherein in the first mode of operation the drive transmission means causes the bush (29) to rotate with the valve stem (23) such that the valve stem rotates without undergoing axial movement and wherein in the second mode of operation the drive transmission means (55) causes relative rotation between the bush (29) and the valve stem (23) such that the valve stem undergoes axial movement while rotating. The apparatus (10) has means including hand wheel (245) for selectively causing the drive transmission means (55) to operate in either one of the first and second modes of operation during rotation of the valve stem (23).

Description

"Valve Grinding"

Field of the Invention

This invention relates to grinding of scale from valves. More particularly, the invention is concerned with an apparatus and method for grinding scale from valves, and also to a valve having provision for grinding scale therefrom.

The invention has been devised particularly, although not necessarily solely, for grinding scale from valves used in alumina processing.

Background Art

In an alumina refinement plant, there are numerous pipelines along which caustic- based liquors are conveyed, with the flow being isolated by valves incorporated in the pipelines. In a typical alumina processing plant, there can be many thousands, and perhaps even tens of thousands, of such valves.

Each valve, which is a type of globe valve commonly known as an angle valve, typically comprises a valve body having an inlet and an outlet between which fluid can flow. The valve body incorporates a valve seat between the inlet and the outlet, as well as a valve member moveable into and out of sealing engagement with the valve seat for closing and opening the valve. The valve member comprises a valve disc supported on one end of a valve stem which can be traversed in order to move the valve disc into and out of sealing engagement with the valve seat.

The valve is required to perform various functions, including (1) valve opening; (2) valve closing; (3) valve locking; (4) valve unlocking; (5) maintaining the valve in a "just open" or throttled condition; and (6) valve grinding (both without advancement of the valve disc with respect to the valve seat and with incremental movement of the valve disc towards the valve seat). Over time, liquors conveyed along the pipelines and through the valves can deposit scale on the internal surfaces of the pipeline and also on the internal surfaces of the valve, particularly the valve body, the valve seat and the valve disc. The accumulation of scale can be detrimental to the operation of the valve, and it is necessary to periodically remove scale accumulating on the valve body, the valve seat and the valve disc. This is commonly achieved by exercising the valve to cause the valve disc to traverse through the valve body and remove any accumulated scale in its path, and also by grinding the scale from the valve disc and the valve seat. Grinding the scale from the valve disc and the valve seat involves rotating the valve disc while it is abutting engagement with the valve seat.

Typically, the valve stem is rotatably supported in a yoke bush with which the valve stem is threadingly engaged. The threaded engagement is provided by the valve stem being externally threaded and the yoke bush being internally threaded, whereby rotation of the valve stem relative to the yoke bush causes axial movement of the valve stem in one direction or the other, according to the direction of rotation of the valve stem. The valve stem is rotated by turning an operating handle fitted onto the outer end of the valve stem. The yoke bush is rotatably supported in the yoke and can be rotated by a locking handle. Turning the locking handle causes the yoke bush to be rotated about the valve stem with which it is in threaded engagement. This causes the valve stem to move axially with respect to the yoke bush. Turning the operating handles rotates the valve stem with respect to the yoke bush, thereby moving the valve disc towards and away from the valve seat.

The steps of locking the valve disc into sealing engagement with the valve seat, and unlocking the valve disc from sealing engagement with the valve seat, are performed using the locking handle. In the valve locking operation, the valve stem is rotated by turning the operating handle so as to move the valve disc into contact with the valve seat. It is, however, not possible to apply enough torque to the valve stem for delivery of sufficient closing force to move the valve disc into sealing engagement with the valve seat. One reason for this is resistance arising through friction between the rotating valve disc and the valve seat. The necessary closing force is therefore delivered using the locking handle. Turning the locking handle (in the appropriate direction) causes the yoke bush to rotate with respect to the valve stem, thereby causing the latter to move axially in the direction towards the valve seat and so carrying the valve disc into sealing engagement with the valve seat. Similarly, the valve unlocking operation is performed using the locking handle. Once the valve has been unlocked to an extent that the valve disc is away from the valve seat, the opening operation can be continued with rotation of the valve stem by turning the operating handle.

It has been found that the torque required to rotate the yoke bush in order to open the valve can be significantly greater than the torque required to close the valve to effect sealing engagement. Indeed, the torque required for valve unlocking can be as much as two to three times greater than the torque required for valve locking. There are several factors which can contribute to the different torque requirements, one being deposition of scale between the valve seat and valve member when the valve is in the closed condition, and another being additional compression forces to which the valve member might be subjected once the valve has been closed (owing to thermal contractions within the valve).

Forces much greater than achievable by an operator without mechanical intervention, are required to operate the valve handles. Accordingly, it is common to use an impact device (such as a sledge hammer, typically of 4Ib or 8Ib nominal weight) to strike the handles to cause them to turn.

The need to turn the locking handle and also the operating handle manually by striking them with means such as a sledge hammer can be exhausting, and also dangerous, for an operator. An operator can, for example, develop injuries through having to swing a heavy sledge hammer for prolonged periods. Further, injuries can also be sustained in cases where an operator does not strike the targeted handle correctly, with the result that the sledge hammer deflects from the handle, or misses the handle altogether, and hits the operator or other personnel, or equipment, in the vicinity.

This can be exacerbated in a valve grinding operation where it is often necessary to strike (by way of the sledge hammer) the operating and locking handles in turn in opposite directions in a repeated manner, over in some instances many hours duration, in order to grind scale deposits from the valve seat and the valve disc to an extent sufficient to provide an acceptable state of sealing engagement.

In view of the problems associated with the need to manually operate the locking handle and also ^"the operating handle, there have been various proposals for arrangements which would allow a valve to be operated in a manner which is less manually intensive and does not require that the locking and operating handles be struck manually with a sledge hammer.

Such proposals typically involve the use of geared mechanisms for driving the yoke bush and also for driving the valve stem. A typical example of such a proposal is disclosed in WO 01/36853.

The proposals typically involve mechanisms for selectively performing either one of two available functions during a valve grinding operation, one function being rotation of the valve stem to cause it undergo axial movement for moving the valve disc into or out of engagement with the valve seat, and the other function being rotation of the valve stem and the yoke bush in a manner which causes the valve disc to rotate with respect to the valve seat for grinding without any axial movement of the valve stem. While such proposals have alleviated much of the manual intensity involved in a valve grinding operation, they do require that the two functions be performed separately; that is, the step of advancing the valve disc into frictional abutment with the valve seat is distinct from the step of rotating the valve stem with respect to the valve seat (without any further advance) to perform the grinding operation, and vice versa.

WO 01/36853 seeks to address such a deficiency by providing an arrangement which can perform the two separate functions, as well as a further function in which the valve disc can rotate with respect to the valve seat and also advance into further frictional engagement with the valve seat at the one time. Such a proposal has not, however, proved to be entirely satisfactory as the rate of advance is directly linked to the rate of rotation of the valve stem. As a consequence of the direct link between advancement of the valve disc and its rotation, there is often stalling of the mechanism because of jamming of the valve disc against the valve seat.

It is against this background, and the problems and difficulties associated therewith, that the present invention has been developed.

The preceding discussion of the background to the invention is intended to facilitate an understanding of the present invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge in Australia as at the priority date of the application.

Disclosure of the Invention

According to a first aspect of the invention there is provided apparatus for use with a valve to perform a grinding operation on the valve, the valve having a valve body defining a valve seat and a valve member moveable into and out of engagement with the valve seat, the valve member comprising a valve disc and a valve stem, and a bush through which the valve stem extends in threaded engagement therewith whereby relative rotation between the bush and the valve stem causes axial displacement of the valve stem relative to the bush, the apparatus comprising a drive transmission means for providing a driving connection to the bush and the valve stem, the drive transmission means having first and second modes of operation, wherein in the first mode of operation the drive transmission means causes the bush to rotate with the valve stem such that the valve rotates without undergoing axial movement and wherein in the second mode of operation the drive transmission means causes relative rotation between the bush and the valve stem such that the valve stem undergoes axial movement while rotating, and means for selectively causing the drive transmission means to operate in either one of the first and second modes of operation during rotation of the valve stem.

Preferably, means are provided for selectively retarding rotation of the bush relative to the valve stem thereby to provide said relative rotation therebetween. Preferably, the apparatus comprises a grinding coupling configured as an attachment to the valve, the grinding coupling having a portion adapted for driving connection to the bush. The valve may, for example, have an operating mechanism comprising a hub mounted on the bush for rotation therewith, in which case said portion of the grinding coupling is adapted from driving connection to the hub.

Preferably, the apparatus further comprises an adaptor configured for driving engagement with the valve stem, whereby rotational torque applied to the adaptor is transmitted to the valve stem. The adaptor is preferably configured to receive driving torque from a driving tool.

The drive transmission means may further comprise a drive sleeve for driving engagement with the adaptor fitted onto the valve stem for rotation therewith. In this regard, the drive sleeve may have an internal spline for mating engagement with an external spline on the adaptor.

The drive sleeve may comprise a section configured as a shaft and a section configured a worm gear.

The grinding coupling may further comprises an actuator sleeve rotatably supported on the shaft section of the drive sleeve for rotation in unison with the valve stem, the actuator sleeve being connected to means for selectively retarding or restraining rotation thereof in unison with the valve stem, the actuator sleeve having a gear, a pinion in meshing engagement with the gear, the pinion being mounted on a lay shaft connected to the hub coupling portion, a two-stage worm comprising a first worm and a second worm in meshing engagement with their rotational axes at right angles, the first worm being mounted on the lay shaft for rotation therewith and the second worm supported on a worm shaft disposed normally to the axis of rotation of the actuator sleeve, the second worm also being in meshing engagement with the worm gear on the drive sleeve. Restraining or retarding rotation of the actuator sleeve has the effect of retarding rotation of the bush relative to the valve stem thereby providing said relative rotation therebetween.

Preferably, said means for selectively retarding or restraining rotation of the actuator sleeve comprises a hand wheel which an operator can restrain or retard.

Preferably, the drive transmission means normally operates in the first mode and is selectively caused to operate in the second mode upon the hand wheel being restrained or retarded.

The portion of the grinding coupling adapted for connection to the hub of the valve operating mechanism may comprise a wall and an annular mounting collar projecting outwardly from the wall, the mounting collar being centred with respect to the axis of rotation of the actuator sleeve about the drive sleeve.

The mounting collar may be provided with an internal spline for mating engagement with an external spline on the hub of the operating mechanism thereby to drivingly interconnect the hub coupling portion and the hub.

The grinding coupling may further comprise a housing comprising said wall and a further wall between which the lay shaft is rotatably supported, said wall being rotatably supported the drive sleeve and said further wall being supported on the drive sleeve.

According to a second aspect of the invention there is provided a grinding coupling for attachment to a valve having a valve body defining a valve seat and a valve member moveable into and out of engagement with the valve seat, the valve member comprising a valve disc and a valve stem, and a bush through which the valve stem extends in threaded engagement therewith whereby relative rotation between the bush and the valve stem causes axial displacement of the valve stem relative to the bush, the grinding coupling being adapted for attachment to the valve, the grinding coupling comprising a drive sleeve for driving engagement with an adaptor fitted onto the valve stem for rotation therewith, the drive sleeve comprising a section configured as a shaft and a section configured as a worm gear, an actuator sleeve rotatably supported on the shaft section of the drive sleeve for rotation in unison with the valve stem, the actuator sleeve being connected to means for selectively retarding or restraining rotation thereof in unison with the valve stem, the actuator sleeve having a gear, a pinion in meshing engagement with the gear, the pinion being mounted on a lay shaft connected to a portion adapted for driving connection to the bush of the valve, a two-stage worm comprising a first worm and a second worm in meshing engagement with their rotational axis at right angles, the first worm being mounted on the lay shaft for rotation therewith and the second worm being supported on a worm shaft disposed normally to the axis of the actuator sleeve, the second worm also being in meshing engagement with the worm gear on the drive shaft.

Preferably, said means for selectively retarding or restraining rotation of the actuator sleeve comprises a hand wheel which an operator can retard or restrain.

The portion adapted for driving connection to the bush of the valve may comprise a hub coupling portion comprising a wall and an annular mounting collar projecting outwardly from the wall, the mounting collar being centred with respect to the axis of rotation of the actuator sleeve about the drive sleeve, the wall supporting one end of the lay shaft.

Preferably, the hub coupling portion is configured for driving engagement with a hub provided on the valve, the hub being drivingly mounted on the bush.

According to a third aspect of the invention there is provided a valve comprising a valve body defining a valve seat and a valve member moveable into and out of engagement with the valve seat, the valve member comprising a valve disc and a valve stem, a first drive input provided on the valve stem for effecting rotation thereof, the valve stem being threadingly engaged with a bush, a drive transmission means drivingly connecting the bush and the valve stem, the drive transmission means having first and second modes of operation, wherein in the first mode of operation the valve stem is rotated without undergoing axial movement and wherein in the second mode of operation the valve stem is rotated and undergoes axial movement, and means for selectively causing the drive transmission means to operate in either one of the first and second modes of operation during rotation of the valve stem.

According to a fourth aspect of the invention there is provided a method of performing a grinding operation on a valve having a valve body defining a valve seat and a valve member moveable into and out of engagement with the valve seat, the valve member comprising a valve disc and a valve stem, and a bush through which the valve stem extends in threaded engagement therewith whereby relative rotation between the bush and the valve stem causes axial displacement of the valve stem relative to the bush, the method comprising advancing the valve disc into abutting engagement with the valve seat and rotating the valve disc while engagement with the valve seat to effect a grinding operation, and selectively during rotation of the valve stem also causing the valve stem to move axially to further advance the valve disc towards the valve seat.

According to a fifth aspect of the invention there is provided an apparatus for use with a valve having a valve body defining a valve seat and a valve member moveable into and out of engagement with the valve seat, the valve member comprising a valve disc and a valve stem, and a bush through which the valve stem extends in threaded engagement therewith whereby relative rotation between the bush and the valve stem causes axial displacement of the valve stem relative to the bush, wherein the apparatus comprises drive transmission means for providing a driving connection to the bush and the valve stem, the drive transmission means having first and second modes of operation, the first mode of operation of the drive transmission means causing the bush to rotate with the valve stem such that the valve rotates without undergoing axial movement and the second mode of operation of the drive transmission means causing relative rotation between the bush and the valve stem such that the valve stem undergoes axial movement while rotating, and means for selectively causing the drive transmission means to operate in either one of the first and second modes of operation during rotation of the valve stem, and wherein the apparatus further comprises an operating mechanism comprising a locking drive input and an unlocking drive input each of which is drivingly connected to the bush, the drive ratio between the respective drive inputs and the bush being different from each other such that a larger torque is delivered to the bush from the unlocking drive input in comparison to the torque delivered to the bush from the locking drive input for the same torque input.

Brief Description of the Drawings

The invention will be better understood by reference to the following description of one specific embodiment as shown in the accompanying drawings in which:

Figure 1 is a schematic sectional side view of a conventional angle valve intended to be modified by apparatus according to the embodiment;

Figure 2 is a perspective view of a gear assembly forming part of apparatus according to the embodiment fitted on to the conventional angle valve;

Figure 3 is a sectional view of the gear assembly fitted on the valve;

Figure 4 is a perspective view of a stem adaptor from one end thereof;

Figure 5 is a perspective view of the stem adaptor from the other end thereof;

Figure 6 is a perspective view of the valve being operated using a gear assembly to which torque is being applied by a driving tool;

Figure 7 is a fragmentary perspective view, illustrating in particular the gear assembly with torque being applied by way of the driving tool for unlocking the valve from the closed condition;

Figure 8 is a view similar to Figure 7, except that torque is being applied to the valve stem by the driving tool for either opening or closing the valve; Figure 9 is a view similar to Figure 8, with the exception that the gear assembly is shown in outline to reveal two mounting plates and a reaction arm attached thereto;

Figure 10 is a view similar to Figure 7, with the exception that the driving tool is shown in a position for locking the valve into the closed condition;

Figure 11 is a schematic view of the gear assembly, showing the position of the driving tool for driving the valve stem, and also showing in broken outline the respective positions of the driving tool for locking and unlocking the valve;

Figure 12 is a schematic perspective view of the gear assembly, showing in particular a gear train incorporated therein;

Figure 13 is a view showing unlocking and initial opening of the valve, with the free end of the valve stem being restrained by a stem anti-rotation mechanism;

Figure 14 is a sectional side view of the stem anti-rotation mechanism illustrated in use in Figure 13;

Figure 15 is a further elevational view of the stem anti-rotation mechanism;

Figure 16 is a sectional side view showing in particular the gear assembly, with the driving tool connected for locking the valve and also a stem adaptor fitted on to the end of the valve stem;

Figure 17 is a schematic perspective view illustrating a grinding coupling fitted into position on the gear assembly, with the driving tool connected to the stem adaptor;

Figure 18 is a perspective view of a grinding coupling from one end thereof; Figure 19 is a perspective view of the grinding coupling from the other end thereof;

Figure 20 is a sectional elevational view of the grinding coupling, with the stem adaptor at one end thereof and part of the gear assembly at the other end thereof being shown in outline;

Figure 21 is a sectional view, on an enlarged scale, of part of the grinding coupling;

Figure 22 is a sectional elevational view of the grinding coupling fitted into position on the gear assembly, with the driving tool connected to the stem adaptor; and

Figure 23 is a view somewhat similar to Figure 17, illustrating the apparatus performing a grinding operation and the hand wheel being retarded by the hand of an operator.

Best Mode(s) for Carrying Out the Invention

The embodiment is directed to apparatus 10 for modifying a conventional short stem angle valve 11 to convert it into a valve having provision for selectively performing the following functions: (1) valve opening; (2) valve closing; (3) valve locking; (4) valve unlocking; (5) maintaining the valve member in a "just open" or throttled condition; and (6) valve grinding (both without advancement of the valve disc with respect to the valve seat and with incremental movement of the valve disc towards the valve seat).

Before describing the apparatus 10 according to the embodiment, it is necessary to consider the conventional angle valve 11 which is to be modified by way of the apparatus. The description of the conventional valve 11 will be made with reference to Figure 1. The conventional angle valve 11 comprises a valve body 13 having an inlet 15, an outlet 17 and a flow path 18 from the inlet 15 to the outlet 17. The body 13 incorporates an annular valve seat 19 adjacent the inlet 15. A valve member 21 is movable into and out of sealing engagement with the valve seat 19 for closing and opening the flow path 18 extending between the inlet 15 and the outlet 17. The valve member 21 comprises a valve stem 23 and a valve disc 25 supported on one end of the valve stem, the valve disc 25 being adapted for sealing engagement with the valve seat 19. The valve stem 23 extends through an opening 26 in the valve body 13 and is supported within a yoke 27 mounted on the valve body 13. The yoke 27 rotatably supports a yoke bush 29 through which the valve stem 23 passes. The yoke bush 29 has a portion 30 incorporating an internal screw thread which engages with an external screw thread 31 on the valve stem 23.

The outer end of the valve stem 23 is fitted with an operating handle 33.

A locking handle 35 is connected to the yoke bush 29. The locking handle 35 has a central hub portion 36 which fits onto a portion 32 the yoke bush 29 and is fixed thereto by a key 37. A lock nut 38 engages the yoke bush 29 to retain the locking handle 35 in position. A lock washer (not shown) locks the nut 38 in position.

Modification of the conventional valve 11 to accommodate the apparatus 10 first involves removal of the operating handle 33, the lock nut 38, the key 37 and the lock washer (not shown). The locking handle 35, and the lock washer are discarded, and the lock nut 38 and the key 37 retained for subsequent use with installation of the apparatus 10. Once these parts of the conventional valve 11 have been removed to provide a stripped version of the valve, various parts of the apparatus 10 are then fitted, as will be described later. With the operating handle

33 removed, a drive spigot 24 on the free end of the valve stem 23 is exposed.

The apparatus 10 according to the embodiment comprises: a gear assembly 41 ; a mounting means 43 incorporating two mounting plates 45, 47; a reaction arm 49 attached to mounting plate 45; a reaction link 51; a stem adaptor 53; a grinding coupling 55; and a stem anti-rotation mechanism 57. The gear assembly 41 is the first component fitted onto the stripped conventional valve 11.

The gear assembly 41 , which is best shown in Figure 3, includes a gear train 61 supported on a base plate 63. The gear train 61 includes a hub 65 adapted to be mounted onto the yoke bush 29, the latter having been retained on the valve stem 23 in the stripped valve 11. The hub 65 is fixed against rotation with respect to the yoke bush 29 by yoke key 37 (which was also retained from the original valve). The hub 65 has a peripheral flange 69 which is configured as a spur gear 71. The hub 65 also has an annular portion 73 which defines a central cavity 75 for receiving the yoke bush nut 35 (retained from the original valve). The yoke bush nut 35 retains the hub 65 in position on the yoke bush 29. The yoke bush nut 35 is retained in position by lock washer 77.

The outer periphery of the annular portion 73 is configured as an external spline 79, the purpose of which will be explained later.

The hub 65 has an inner face 81 which confronts the base plate 63 and in which there are recesses 83 accommodating friction pads 85 which frictionally engage the base plate 63. Interaction between the friction pads 85 on the hub 65 and the base plate 63 serves to resist rotation of the hub 65 (and hence the yoke bush 29 to which it is connected) until sufficient rotational force is applied to the hub.

The gear train 61 further comprises a first pinion 91 in meshing engagement with the spur gear 71. The first pinion 91 is configured as part of a first rotatable element 93. The first rotatable element 93 is also configured to provide an intermediate gear 95 and a stub shaft 97 which is rotatably supported within a support sleeve 99 attached to the opposed side of the base plate 63. A bush 101 of appropriate low-friction material is provided between the stub shaft 97 and the support sleeve 99.

The end of the rotatable element 93 opposite to the stub shaft 97 has a protrusion 107 in which there is incorporated a locking drive input configured as a drive socket 109. In this embodiment, the locking drive socket 109 is configured as a female ³/₄" drive facility.

The intermediate gear 95 is in meshing engagement with a second pinion 111 which forms part of a second rotatable element 113. The second rotatable element 113 is configured to provide a stub shaft 115 which is rotatably supported within a support sleeve 117 mounted on the base plate 63. The end of the second rotatable element 113 opposite to the stub shaft 115 is connected to a unlocking drive input configured as a drive socket 119 through a ratchet mechanism 121 which provides for unlocking only. In this embodiment, the unlocking drive socket 119 is configured as a female ³Z₄" drive facility. The ratchet mechanism 121 is arranged to transmit rotational torque to the second rotatable element 113 (and hence to the second pinion 111 ) upon rotation in one direction and to free-wheel upon rotation in the other direction so as not to transmit any rotational torque to the second rotatable element 113.

The gear train 61 thus drivingly connects both the locking drive socket 109 and the unlocking drive socket 119 to the yoke bush 29. The locking drive socket 109 is used to rotate the yoke bush 29 in a direction to cause locking of the valve; that is, to move the valve disc 25 into sealing engagement with the valve seat 19 without rotation of the valve stem 23. Similarly, unlocking drive socket 119 is used for unlocking the valve; that is, to move the valve member 21 into a "just open" or throttled position (in which the valve disc 25 is out of sealing engagement with the valve seat 19) without rotation of the valve stem 23.

The separate drive sockets 109, 119 are provided for locking and unlocking the valve as different torques are required for such purposes. By way of explanation, the torque required to rotate the yoke bush 29 in order to unlock the valve from the closed condition can be significantly greater than the torque required to lock the valve in the closed condition to effect sealing engagement. Indeed, the torque required for valve unlocking can be as much as two to three times greater than the torque required for valve locking. There are several factors which can contribute to the different torque requirements, one being deposition of scale between the valve seat 19 and valve member 21 when the valve is in the closed condition, and another being additional compression forces to which the valve member 21 might be subjected once the valve has been closed (owing to thermal contractions within the valve). In order to accommodate the different torque requirements, the gear ratios between the yoke bush 29 and the respective drive sockets 109, 119 are different. More particularly, the presence of the second pinion 111 and intermediate gear 95 in which it is meshing engagement provide the additional torque requirements. The ratchet mechanism 121 is associated with the unlocking drive socket 119 to ensure that the latter can only be used for unlocking the valve. Because the ratchet mechanism 121 does not transmit rotational torque when the unlocking drive socket 119 is rotated in the other direction, the unlocking drive socket cannot be utilised for locking the valve. This is a safety feature, as use of the unlocking drive socket 119 to lock the valve could exert such a compression force between the valve member 21 and the valve seat 19 that extreme torque may be necessary in order to subsequently unlock the valve (having regard to the fact that torque requirements to unlock a valve are significantly greater than the torque requirements for locking a valve).

The gear assembly 41 also includes a cover 123 which provides a protective shroud about the gear train 61.

As mentioned previously, the gear assembly 41 is the first component of the apparatus 10 to be fitted to the stripped valve. Once the gear assembly 41 is fitted in position, the mounting plates 45, 47 are then positioned on opposed sides of the yoke 27 and clamped in position by way of clamping bolts 131. As the yoke

27 is a casting, it may be necessary to grind the opposed faces of the casting to ensure that they are sufficiently flat in order to receive the mounting plates 45, 47. If this is necessary, the grinding operation is performed prior to installation of the gear assembly 41.

Installation of the reaction arm 49 is achieved with installation of the mounting plates 45, 47, as the reaction arm 49 is attached to mounting plate 45. The reaction arm 49 comprises two sections, being an inner section 133 fixed to mounting plate 45, and an outer section 135 slidably supported in a mounting sleeve 136 on the inner section 133. The outer section 135 is slidably moveable with respect to the inner section 133 between operating and retracted conditions. A locking mechanism (not shown) is provided for selectively locking the outer section 135 in either the operating condition or the retracted condition. In the retracted condition, the reaction arm outer section 135 is stowed (so as to be less likely to impose an impediment to movement around the valve).

The mounting plates 45, 47 include mounting flanges 141 to which the base plate 63 of the gear assembly 41 can be connected by way of mounting bolts 143.

The stem adaptor 53, which is best seen in Figures 4 and 5, comprises a cylindrical body 151 with a socket 153 at one end thereof for drivingly engaging drive spigot 24 on the free end of the valve stem 23. The other end of the cylindrical body 151 incorporates a drive socket 155 which in this embodiment is configured as a female ³/₄" drive facility. The cylindrical body 151 also includes an external spline 157 on its cylindrical periphery.

The drive socket 155 in the stem adaptor 53, and also the locking drive socket 109 and the unlocking drive socket 119 in the gear assembly 41 , are each adapted to receive a driving tool 160. In this way, the driving tool 160 can be applied to any one of the drive sockets 109, 119 and 155 at the time that rotational torque is required to be applied thereto. In this embodiment, the driving tool 160 has a ³Z₄" drive spigot for mating engagement with the sockets 109, 119 and 155 within the various female ³/₄" drive facilities. While the driving tool 160 can take any appropriate form, it is particularly convenient that it be an air- operated torque gun. In Figure 7, the driving tool 160 is shown connected to the unlocking drive socket 119, and in Figure 10, the driving tool 160 is shown drivingly connected to the locking drive socket 109. In Figures 8 and 9, it is shown drivingly connected to the drive socket 155 of the stem adaptor 53.

It is particularly advantageous that the apparatus 10 utilise female ³U" drive facilities, as this serves to restrict the type of driving tool 160 that can be conveniently used. For example, the female ³Z₄" drive facility provides a deterrent against use of a more powerful driving tool which would normally be fitted with a different drive spigot. In order to be able to use the more powerful tool, it would be necessary to replace its drive spigot with one compatible with the female ³A*" drive. The need to locate and then fit the replacement drive spigot to the more powerful driving tool is likely to in itself provide a deterrent to use of the more powerful tool.

Reaction torque arising from operation of the driving tool 160 is transferred to the reaction arm 49 by way of the reaction link mechanism 51. In this way, an operator holding the driving tool 160 merely has to guide the tool during its operation and does not have to counteract any reaction torque.

The reaction link 51 comprises a rigid arm 171 at one end of which there is provided a collar 173 having an internal spline in engagement with a matching external spline (not shown) on the body of the driving tool 160. In this way, the arm 171 can rotate in unison with the body of the driving tool. The other end of the arm 171 incorporates a sleeve 175 which is elongated in the longitudinal direction of the arm 171. The sleeve 175 is adapted to be received on the outer section 135 of the reaction arm 49. Because of the elongate configuration of the sleeve 175, the rigid arm 171 can move axially with respect to the reaction arm outer section 135. This arrangement allows the driving tool 160 to move laterally to a limited extent, as determined by the length of the elongated sleeve 175. The reaction mechanism 51 can also move along the reaction arm outer section 135. In this way, the driving tool 160 can be moved into driving engagement with any one of the drive sockets 109, 119 and 155 while still being connected to the reaction arm 49 via the reaction link mechanism 51. Further, the driving tool 160 can be suspended from the reaction arm outer section 135 by the reaction link mechanism 51 when not connected to any of the drive sockets 109, 119 and 155. In other words, the operator can release the driving tool 160 and, rather than put it aside, can simply allow it to swing from the reaction arm 49 so that it is readily accessible when next required for use during the valve grinding operation.

With the valve 10 modified in this way, various functions relating to operation of the valve can be performed using the driving tool 160 in engagement with the drive sockets 109, 119, and also drive socket 155 when the stem adaptor 53 is mounted on the end of the valve stem 23. For example, when the valve is in the locked condition, the valve member 21 can be moved away from the valve seat 19 to "crack open" the valve by applying drive to the unlocking drive socket 119. As previously mentioned, drive can be transmitted from the unlocking drive socket 119 to the yoke bush 29 in a direction which causes the valve stem 23 to move axially away from the valve seat 19 and thereby "crack open" the valve. During this process, the yoke bush 29 rotates relative to the valve stem 23; the valve stem 23 itself does not rotate but rather merely moves axially. The valve can then be further opened by fitting the stem adaptor 53 on to the end of the valve stem 23 and then engaging the driving tool 160 with the drive socket 155 in the stem adaptor. The driving tool 160 then drives the valve stem 23, causing it to rotate relative to the yoke bush 29. Because of the threaded engagement between the valve stem 23 and the yoke bush 29, such rotation causes the valve stem 23 to wind outwardly, carrying the valve disc 25 away from the valve seat 19 in the conventional manner. When the valve is open to the required extent, operation of the driving tool 160 is terminated and it is disengaged from the drive socket 155. The stem adaptor 53 can then be removed. At some later stage, when it is desired to close the valve, the stem adaptor 53 is again positioned on the valve stem 23 and drive applied to the drive socket 155 by way of the driving tool 160 in a direction to cause the valve stem 23 to wind inwardly and carry the valve disc 25 towards the valve seat 19. During this process, the valve stem 23 rotates relative to the yoke bush 29 and moves axially inwardly.

When the valve stem 23 is being rotated by the drive tool 160 relative to the yoke bush 29, the latter is restrained from rotation with the valve stem 23 as a result of frictional effects and inertia within the gear train 61 , including in particular the frictional effects between the friction pads 85 carried on the hub 65 and the base plate 63.

Once the valve disc 25 has moved into contact with the valve seat 19, locking torque which could be applied to the valve stem 23 by the driving tool 160 via the stem adaptor 53 is not of sufficient magnitude to establish sealing engagement between the valve member 21 and the valve seat 19. One reason for this is that the frictional effects between the valve disc 25 and valve seat 19 arising through rotation of the valve disc relative to the valve seat 19 are of such an extent that the necessary locking torque cannot be delivered via the valve stem 23. The locking operation of the valve is therefore performed by applying drive via the driving tool 160 to the locking drive socket 109. Torque applied through the locking drive socket 109 is transmitted by the gear train 61 to the yoke bush 29, causing the yoke bush to rotate. Rotation of the yoke bush 29 relative to the valve stem 23 causes the valve stem to move axially in a direction towards the valve seat 19, thereby carrying the valve disc 25 into locking engagement with the valve seat 19.

In certain circumstances, it may be necessary to restrain the valve stem 23 against uncontrolled rotation when the valve is being unlocked; that is, when the valve is being "cracked open" into a throttled condition. This is because rapid flow of liquor under pressure through the "cracked open" valve can cause the valve member 21 , and in particular the valve stem 23, to vibrate. This vibration of the valve stem 23 can induce rotation into the valve member 21 , possibly causing the valve to open rapidly and also presenting a potential danger to an operator. The stem anti-rotation mechanism 57 is provided for restraining the valve member 21 against rotation in circumstances where this may be necessary, as shown in Figure 15. The stem anti-rotation mechanism 57 comprises an arm 181 one end of which is fitted with a socket member 183 adapted to engage the spigot 24 on the end of the valve stem 23. The other end of the arm 181 is fitted with a sleeve 185 adapted for location on the outer section 135 of the reaction arm 49. In this way, the arm 181 interconnects the valve stem 23 and the reaction arm 49, thereby preventing rotation of the valve stem 23.

The socket member 183 incorporates a ratchet mechanism 187 which allows the socket member to be selectively rotated for alignment with the spigot 24 on the end of the valve stem 23 to achieve engagement therewith. The ratchet mechanism 187 has a locking lever 189 moveable between engaged and disengaged positions. When the locking lever 189 is disengaged, the ratchet mechanism 187 allows rotation of the socket member 183 so that it is correctly oriented for registration with the drive spigot 24 on the end of the valve stem 23.

Once the socket member 183 is in position on the end of the valve stem 23, the locking lever 189 is engaged, thereby restraining the socket member 183 against further rotation with respect to the arm 181.

Over time, liquor passing through the valve can deposit scale on the internal surfaces of the valve, including in particular the valve seat 19 and valve disc 25. The accumulation of the scale can be detrimental to the operational performance of the valve, and it is necessary to periodically remove the accumulated scale by grinding the scale from the valve disc and the valve seat. In order to perform the necessary grinding operation, the grinding coupling 55 is fitted in position.

The grinding coupling 55, which is best seen in Figures 18, 19 and 20, comprises a drive sleeve 201 having a central passage 203 through one end of which the stem adaptor 53 can be received (as shown in outline in Figure 20). The drive sleeve 201 is provided with an internal spline 205 matching the external spline

157 on the stem adaptor 53 for engagement therewith. The drive sleeve 201 comprises a first section configured as a first shaft 207 adjacent one end, a second section configured as a second shaft 209 adjacent the other end, and a third section intermediate the first and second sections configured as a worm gear

211.

The grinding coupling 55 further comprises an actuator sleeve 213 rotatably supported on the first shaft 207 by way of bushes 215. The actuator sleeve 213 has an external spline 217 adjacent one end thereof and a flange 219 adjacent the other end thereof configured as a spur gear 221.

The spur gear 221 is in meshing engagement with a pinion 223 mounted on a shaft 225. The shaft 225 is supported within a housing 227. The housing 227 has two opposed walls 228, 229 between which the shaft 225 is rotatably supported, wall 228 is rotatably supported on the actuator sleeve 213 adjacent to the flange 219 by bush 226, and wall 229 is rotatably supported on the second shaft 209 of the drive sleeve 201 by bush 328.

A two-stage worm 230 is accommodated within the housing 227, the two-stage worm comprising a first worm 231 and a second worm 232, with the two worms being in meshing engagement and their rotational axes at right angles. The first worm 231 is mounted on the shaft 225 for rotation therewith. The second worm 232 is supported on a worm shaft 233 disposed at right angles to the axis of rotation of shaft 225 and in effect tangential to the axis of rotation of the actuator sleeve 213. In addition to being in meshing engagement with the first worm 231 , the second worm 232 is in meshing engagement with the worm gear 211 on the drive sleeve 201.

An annular mounting collar 241 projects outwardly from wall 229 of housing 227. The mounting collar 241 is centred with respect to the axis of rotation of the actuator sleeve 213 about the drive sleeve 201. The mounting collar 241 is provided with an internal spline 243 for matching engagement with the external spline 79 on the annular portion 73 of hub 65 of the gear assembly 41.

The grinding coupling 55 further comprises a hand wheel 245 mounted on the actuator sleeve 213. The hand wheel 245 incorporates an internal spline 247 for engagement with the external spline 217 of the actuator sleeve 213. The hand wheel 245 is retained in position on the actuator sleeve 213 by circlips 249.

When a grinding operation is to be preformed on the valve, the grinding coupling 55 is installed in position. This involves the grinding coupling 55 being positioned on the gear assembly 41 , as shown in Figure 22, with the internal spline 243 of the mounting collar 241 engaging with the external spline 79 of the hub 65 of the gear assembly. Further, the grinding coupling 55 is installed such that the internal spline 205 on the drive sleeve 201 engages with the external spline 157 of the stem adaptor 53 positioned on the free end of the valve stem 23. In fitting the grinding coupling 55 in position in this way, it may be necessary to rotate the hand wheel 245 back and forth a little in order to achieve registration between the respective splines.

Once the grinding coupling 55 is fitted in position as described, the grinding operation can be performed. This is done by engaging the drive tool 160 with the drive socket 155 in the outer end of the stem adaptor 53, as shown in Figure 22 and 23. The drive tool 160 is operated to cause the valve stem 23 to rotate and thereby rotate the valve disc 25 with respect to the valve seat 19 for grinding scale therebetween. As the stem adaptor 53 rotates, it not only transmits rotary motion to the valve stem 23 but also to the drive sleeve 201 with which it is drivingly interconnected by way of the interconnected splines 157 and 205. As the drive sleeve 201 rotates so does the worm gear 211 which forms part of the drive sleeve. The worm gear 211 transmits drive to the second worm 232 with which it is in engagement. However, as the axis of rotation of the second worm 232 is normal to the axis of rotation of the worm gear 211 , the second worm gear 232 is not caused to rotate but rather acts as a fixed element through which drive is transmitted. Drive transmitted through the second worm gear 232 is also transmitted to the first worm gear 231. Again, as the axis of rotation of the first worm gear 231 is normal to the axis of rotation of the second worm gear 232, the first worm gear 231 also does not rotate but rather simply acts as a fixed element through which drive is transmitted to the shaft 225 supported between the walls 228, 229 of the housing. Again, there is direct transmission of the drive to the shaft 225 which in turn directly transfers the drive to the housing 227. From the housing 227, the drive is transferred to the mounting collar 241. Accordingly, there is a direct driving connection between the mounting collar 241 and the stem adaptor 53. In other words, the mounting collar 241 rotates at the same angular velocity as the stem adaptor 53 and the valve stem 23 connected thereto. The actuator sleeve 213, and the hand wheel 245 connected thereto, also rotate in unison with the drive sleeve 201 because of the meshing engagement between pinion 223 and spur gear 221. There is no relative rotation between the pinion 223 and spur gear 221 at this stage, and so there is a fixed drive connection therebetween.

Drive from the mounting collar 241 is transferred directly to the hub 65 of the gear assembly 41 by way of the engaging splines 243, 79. Rotation of the hub 65 is transmitted to the yoke bush 29 to which it is keyed. With this arrangement, the yoke bush 29 is caused to rotate at the same angular velocity as the valve stem 23. In this way, there is no relative rotation between the valve stem 23 and the yoke bush 29. Accordingly, there is no axial movement of the valve stem 23 and the grinding process involves simply rotation of the valve disc 25 with respect to the valve seat 19 (there being no advancement of the valve member towards the valve seat).

When it is desired to cause the valve disc 25 to advance further into engagement with the valve seat 19, it is necessary to initiate some relative movement between the valve stem 23 and the yoke bush 29 in a direction to cause the desired axial movement of the valve stem 23. This can be achieved during the valve grinding process by the operator merely restraining, or retarding rotation of, the hand wheel 245. The operator can, for example, grasp the hand wheel 245 by hand

246 in order to restrain its rotation, or alternatively simply apply pressure to the hand wheel in order to retard its rotation.

With the hand wheel 245 being restrained or retarded, the drive sleeve 201 is caused to rotate relative to the actuator sleeve 213. The relative movement between the actuator sleeve 213 and the drive sleeve 201 causes the worm gear 211 to rotate relative to the second worm 232 with which it is in meshing engagement. This applies rotational drive to the second worm 232 which in turn is transmitted to the first worm 231 with which the second worm 232 is in meshing engagement. The rotation of the worm gear 211 and the two worms 231 , 232 causes shaft 225 to rotate, with the result that the pinion 223 thereon also rotates, producing relative rotation between pinion 223 and spur gear 221. This interrupts the direct driving relationship between the stem adaptor 53 and the mounting collar 241. This interruption of the direct driving relationship provides some retardation of rotation of the mounting collar 241 with respect to the stem adaptor 53. As a consequence, the angular velocity of the mounting collar 241 is now marginally lower than the angular velocity of the valve stem 23. As drive from the mounting collar 241 is transmitted to the yoke bush 29, the yoke bush 29 is also caused to rotate at an angular velocity marginally slower than that of the valve stem 23. This difference in the angular velocities of the valve stem 23 and the yoke bush 29 result in relative movement therebetween, a consequence of which is that there is axial movement of the valve stem 23 with respect to the yoke bush, thereby advancing the valve member 21 , and more particularly the valve disc 25, towards the valve seat 19. The hand wheel 245 is so dimensioned that when the grinding coupling 55 is installed in position, it blocks access to drive sockets 109, 119. In this way, the drive tool 160 cannot engage and apply drive to the drive sockets 109, 119 when a grinding operation is being performed.

It is a particular feature of this arrangement that the operator can selectively cause the valve disc 25 to incrementally advance towards the valve seat 19 during the grinding operation, simply by manipulating the hand wheel 245. Further, if during the grinding operation the valve disc 25 frictionally engages the valve seat 19 to such an extent that there is a possibility of overloading or stall, the operator can simply rotate the hand wheel 245 in the reverse direction, causing the valve disc 25 to incrementally retract from the valve seat 19 to remove potential for the overload or stall condition.

The grinding operation continues, with rotation of the valve stem 23 causing rotation of the valve disc 25 for grinding without incremental advance. When the grinding operation is at a stage that it is necessary to advance the valve disc 25 towards the valve seat 19, it is merely necessary for the operator to restrain or retard the hand wheel 245 as previously described in order to effect the necessary advance.

Once the grinding operation has been completed, the grinding coupling 55 and also the stem adaptor 53 are removed. The valve can then be operated as previously described when necessary, using the driving tool 160 in engagement with the locking drive socket 109 and the unlocking drive socket 119 as necessary. When the valve stem 23 is required to be rotated, it will be necessary to install the stem adaptor 53 in order to use the driving tool 160 to rotate the valve stem.

From the foregoing, it is evident that the present embodiment provides a simple yet highly effective arrangement for performing the various valve functions described previously; namely (1) valve opening; (2) valve closing; (3) valve locking; (4) valve unlocking; (5) maintaining the valve member in a "just open" or throttled condition; and (6) valve grinding (both without advancement of the valve disc with respect to the valve seat and with incremental movement of the valve disc towards the valve seat).

Further, a grinding operation can be performed on the valve in-situ, in conditions that are less arduous and somewhat safer for the operator. The grinding operation can be performed more conveniently and more quickly, as incremental movement of the valve disc towards the valve seat can be performed as necessary during the grinding operation without any interruption to the grinding process.

A still further advantage is that a conventional angle valve can be converted in- situ using the apparatus 10 according to the embodiment and without interruption to operation of the valve. The conversion process can be performed in-situ without the need for specialised equipment or specialised machining processes. For example, the yoke bush 29 of the conventional valve 11 is retained, and the hub 65 is fixed to the yoke bush 29 using the key 37 inserted in the keyway in the yoke bush 29 previously used to fix the locking handle 35 in position. In other words, many existing features of the conventional valve 11 are utilised in the conversion process to facilitate an arrangement which is conducive to a convenient in situ conversion.

It should be appreciated that the scope of the invention is not limited to the scope of the embodiment described.

While the embodiment has been described with respect to apparatus for modifying a conventional short stem angle valve, it should be understood that the invention may have application to other valves, including long stem valves. Further, while the embodiment has been described with reference to modification of existing valves, the invention may also be incorporated into original equipment manufacture; that is, a valve could be constructed to incorporate the invention.

Modifications and changes may be made without departing from the scope of the invention. Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

The Claims Defining the Invention are as Follows:

1. Apparatus for use with a valve to perform a grinding operation on the valve, the valve having a valve body defining a valve seat and a valve member moveable into and out of engagement with the valve seat, the valve member comprising a valve disc and a valve stem, and a bush through which the valve stem extends in threaded engagement therewith whereby relative rotation between the bush and the valve stem causes axial displacement of the valve stem relative to the bush, the apparatus comprising a drive transmission means for providing a driving connection to the bush and the valve stem, the drive transmission means having first and second modes of operation, wherein in the first mode of operation the drive transmission means causes the bush to rotate with the valve stem such that the valve stem rotates without undergoing axial movement and wherein in the second mode of operation the drive transmission means causes relative rotation between the bush and the valve stem such that the valve stem undergoes axial movement while rotating, and means for selectively causing the drive transmission means to operate in either one of the first and second modes of operation during rotation of the valve stem.

2. Apparatus according to claim 1 further comprising means for selectively retarding rotation of the bush relative to the valve stem thereby to provide said relative rotation therebetween.

3. Apparatus according to claim 1 or 2 further comprising a grinding coupling configured as an attachment to the valve, the grinding coupling having a portion adapted for driving connection to the bush.

4. Apparatus according to claim 3 wherein the valve has an operating mechanism comprising a hub mounted on the bush for rotation therewith, and wherein said portion of the grinding coupling is adapted from driving connection to the hub.

5. Apparatus according to any one of the preceding claims further comprising an adaptor configured for driving engagement with the valve stem, whereby rotational torque applied to the adaptor is transmitted to the valve stem.

6. Apparatus according to claim 5 wherein the adaptor is configured to receive driving torque from a driving tool.

7. Apparatus according to claim 5 or 6 wherein the drive transmission means r comprising a drive sleeve for driving engagement with the adaptor fitted onto the valve stem for rotation therewith.

8. Apparatus according to claim 7 wherein the drive sleeve has an internal spline for mating engagement with an external spline on the adaptor.

9. Apparatus according to claim 7 or 8 wherein the drive sleeve comprises a section configured as a shaft and a section configured a worm gear.

10. Apparatus according to claim 9 wherein the drive transmission means further comprises an actuator sleeve rotatably supported on the shaft section of the drive sleeve for rotation in unison with the valve stem, the actuator sleeve being connected to means for selectively retarding or restraining rotation thereof in unison with the valve stem, the actuator sleeve having a gear, a pinion in meshing engagement with the gear, the pinion being mounted on a lay shaft connected to the hub coupling portion, a two-stage worm comprising a first worm and a second worm in meshing engagement with their rotational axes at right angles, the first worm being mounted on the lay shaft for rotation therewith and the second worm supported on a worm shaft disposed normally to the axis of rotation of the actuator sleeve, the second worm also being in meshing engagement with the worm gear on the drive sleeve.

11. Apparatus according to claim 10 wherein the drive transmission means is adapted to normally operate in the first mode and be selectively caused to operate in the second mode upon actuation of said means for selectively retarding or restraining rotation of the actuator sleeve.

12. Apparatus according to claim 10 or 11 wherein said means for selectively retarding or restraining rotation of the actuator sleeve comprises a hand wheel which an operator can restrain or retard.

13. Apparatus according to any one of claims 4 to 12 wherein said portion of the grinding coupling adapted for connection to the hub of the valve operating mechanism comprises a wall and an annular mounting collar projecting outwardly from the wall, the mounting collar being centred with respect to the axis of rotation of the actuator sleeve about the drive sleeve.

14. Apparatus according to claim 13 wherein the mounting collar has an internal spline for mating engagement with an external spline on the hub of the operating mechanism thereby to drivingly interconnect the hub coupling portion and the hub.

15. Apparatus according to claim 13 or 14 wherein the grinding coupling further comprises a housing comprising said wall and a further wall between which the lay shaft is rotatably supported, said wall being rotatably supported the drive sleeve and said further wall being supported on the drive sleeve.

16. A grinding coupling for attachment to a valve having a valve body defining a valve seat and a valve member moveable into and out of engagement with the valve seat, the valve member comprising a valve disc and a valve stem, and a bush through which the valve stem extends in threaded engagement therewith whereby relative rotation between the bush and the valve stem causes axial displacement of the valve stem relative to the bush, the grinding coupling being adapted for attachment to the valve, the grinding coupling comprising a drive sleeve for driving engagement with an adaptor fitted onto the valve stem for rotation therewith, the drive sleeve comprising a section configured as a shaft and a section configured as a worm gear, an actuator sleeve rotatably supported on the shaft section of the drive sleeve for rotation in unison with the valve stem, the actuator sleeve being connected to means for selectively retarding or restraining rotation thereof in unison with the valve stem, the actuator sleeve having a gear, a pinion in meshing engagement with the gear, the pinion being mounted on a lay shaft connected to a portion adapted for driving connection to the bush of the valve, a two-stage worm comprising a first worm and a second worm in meshing engagement with their rotational axis at right angles, the first worm being mounted on the lay shaft for rotation therewith and the second worm being supported on a worm shaft disposed normally to the axis of the actuator sleeve, the second worm also being in meshing engagement with the worm gear on the drive shaft.

17. A grinding coupling according to claim 16 wherein said means for selectively retarding or restraining rotation of the actuator sleeve comprises a hand wheel which an operator can retard or restrain.

18. A grinding coupling according to claim 16 or 17 wherein said portion adapted for driving connection to the bush of the valve comprises a hub coupling portion comprising a wall and an annular mounting collar projecting outwardly from the wall, the mounting collar being centred with respect to the axis of rotation of the actuator sleeve about the drive sleeve, the wall supporting one end of the lay shaft.

19. A grinding coupling to claim 18 wherein the hub coupling portion is configured for driving engagement with a hub provided on the valve, the hub being drivingly mounted on the bush.

20. A valve comprising a valve body defining a valve seat and a valve member moveable into and out of engagement with the valve seat, the valve member comprising a valve disc and a valve stem, a first drive input provided on the valve stem for effecting rotation thereof, the valve stem being threadingly engaged with a bush, a drive transmission means drivingly connecting the bush and the valve stem, the drive transmission means having first and second modes of operation, wherein in the first mode of operation the valve stem is rotated without undergoing axial movement and wherein in the second mode of operation the valve stem is rotated and undergoes axial movement, and means for selectively causing the drive transmission means to operate in either one of the first and second modes of operation during rotation of the valve stem.

21. A valve according to claim 20 further comprising means for selectively retarding rotation of the bush relative to the valve stem thereby to provide said relative rotation therebetween.

22. A valve according to claim 20 or 21 further comprising a locking drive input and an unlocking drive input each of which is drivingly connected to the bush, the drive ratio between the respective drive inputs and the bush being different from each other such that a larger torque is delivered to the bush from the unlocking drive input in comparison to the torque delivered to the bush from the locking drive input for the same torque input.

23. A valve according to claim 23 wherein the locking drive input and an unlocking drive input are each drivingly connected to the bush through a gear train, the gear ratio between the respective drive inputs and the bush being different from each other to provide the different drive ratios.

24. A valve according to claim 24 wherein the gear train comprises a bush drive gear connected to the bush whereby rotation of the bush drive gear imparts rotary motion to the bush.

25. A valve according to claim 24 or 24 wherein the gear train is supported on a base plate.

26. A valve according to any one of claims 23 to 26 further comprising a hub mounted on the bush for rotation therewith, the hub being configured to define the bush drive gear.

27. A valve according to claim 25, 26 or 27 wherein the gear train comprises the bush drive gear in meshing engagement with a first pinion to which the locking drive input is driving connected, the pinion being connected to an intermediate gear for rotation therewith, the intermediate gear being in meshing engagement with a second pinion to which the unlocking drive input is drivingly connected..

28. A valve according to claim 28 wherein the unlocking drive input is drivingly connected to the second pinion through a ratchet adapted to transmit rotational torque to the second pinion upon rotation of the unlocking drive input in one direction and adapted to free-wheel upon rotation of the unlocking drive input in the other direction so as not to transmit any rotational torque to the second pinion.

29. A valve according to claim 27, 28 or 29 wherein the hub has a peripheral flange configured as a spur gear which provides the bush gear.

30. A valve according to any one of claims 27 to 30 wherein the hub has an annular portion which defines a central cavity for receiving a retaining nut to threadingly engage the bush and retain the hub in position on the bush.

31. A valve according to claim 31 wherein the outer periphery of the annular portion is configured as an external spline.

32. A valve according to any one of claims 27 to 32 when dependent on claim 26 wherein the hub has an inner face confronting the base plate on which the gear train is supported.

33. A valve according to claim 31 wherein the hub is in frictional engagement with the base plate.

34. A valve according to any one of claims 28 to 34 wherein the first pinion and the intermediate gear are each be defined by a first rotatable element.

35. A valve according to claim 35 wherein the first rotatable element also defines a stub shaft which is rotatably supported within a first support sleeve on the base plate.

36. A valve according to claim 36 wherein the end of the first rotatable element opposite to the stub shaft incorporates the locking drive socket.

37. A valve according to any one of claims 28 to 37 wherein the second pinion is defined by a second rotatable element.

38. A valve according to claim 38 wherein the second rotatable element also defines a stub shaft which is rotatably supported within a second support sleeve on the base plate.

39. A valve according to claim 39 wherein the end of the second rotatable element opposite to the stub shaft is connected to the unlocking drive socket.

40. A valve according to any one of claims 23 to 40 further comprising a cover about the gear train, and wherein the locking and unlocking drive sockets and also the annular portion of the hub each extend outwardly to the exterior of the cover.

41. A method of performing a grinding operation on a valve having a valve body defining a valve seat and a valve member moveable into and out of engagement with the valve seat, the valve member comprising a valve disc and a valve stem, and a bush through which the valve stem extends in threaded engagement therewith whereby relative rotation between the bush and the valve stem causes axial displacement of the valve stem relative to the bush, the method comprising advancing the valve disc into abutting engagement with the valve seat and rotating the valve disc while engagement with the valve seat to effect a grinding operation, and selectively during rotation of the valve stem also causing the valve stem to move axially to further advance the valve disc towards the valve seat.

42. Apparatus for use with a valve having a valve body defining a valve seat and a valve member moveable into and out of engagement with the valve seat, the valve member comprising a valve disc and a valve stem, and a bush through which the valve stem extends in threaded engagement therewith whereby relative rotation between the bush and the valve stem causes axial displacement of the valve stem relative to the bush, wherein the apparatus comprises drive transmission means for providing a driving connection to the bush and the valve stem, the drive transmission means having first and second modes of operation, the first mode of operation of the drive transmission means causing the bush to rotate with the valve stem such that the valve rotates without undergoing axial movement and the second mode of operation of the drive transmission means causing relative rotation between the bush and the valve stem such that the valve stem undergoes axial movement while rotating, and means for selectively causing the drive transmission means to operate in either one of the first and second modes of operation during rotation of the valve stem, and wherein the apparatus further comprises an operating mechanism comprising a locking drive input and an unlocking drive input each of which is drivingly connected to the bush, the drive ratio between the respective drive inputs and the bush being different from each other such that a larger torque is delivered to the bush from the unlocking drive input in comparison to the torque delivered to the bush from the locking drive input for the same torque input.

43. Apparatus for use with a valve to perform a grinding operation on the valve, the apparatus being substantially as herein described with reference to the accompanying drawings.

44. A grinding coupling substantially as herein described with reference to the accompanying drawings.

45. A valve substantially as herein described with reference to the accompanying drawings.

46. A method of performing a grinding operation substantially as herein described.