Patent Publication Number: US-6213148-B1

Title: Valve lock and adapter

Description:
The present invention relates to a valve lock for locking a valve spindle in a selected position relative to a valve body, and to an adapter for interengaging for example a valve lock assembly and a valve spindle. 
     Valve locks are required to provide a means for locking a rotatable valve spindle in a pre-determined position. For example, in industrial installations in which potentially hazardous fluids are pumped through process equipment, it is often necessary to secure a series of valves in a particular configuration. Valves are locked both to prevent unauthorised operation and, where a series of valves are interlocked, to prevent the sequential operation of a series of valves in a potentially dangerous manner. In an interlocked system, there may be for example three valves which must be opened in a pre-determined sequence. In such a system, it is known to provide a key on the first valve in the sequence which can only be removed once that valve has been opened, that key then being used to release a second valve to enable that second valve to be opened, and a further key mounted on the second valve then being released to enable the third valve to be opened. Such key-operated mechanisms are widely used in the process control industry, and one such mechanism is described in British patent specification number 2292207. 
     Where a valve lock has a captive key that can only be removed once the valve has been fully closed, the mechanism requires a valve spindle position indicating mechanism which prevents key removal until the valve spindle has been rotated to a pre-determined axial and rotational position. Such mechanisms are often referred to as “counters” as in effect it is necessary to pre-set the position of the spindle at which the kev is to be released, to count rotations of the spindle away from that initial position, and then to count rotations of the spindle back to the initial position. Thus rotation of the valve spindle is tracked by the counting mechanism such that when the valve spindle is returned to its initial position the valve position counting mechanism indicates that this is the case and releases the key. 
     One problem with the valve position indicator systems of known valve locks is that of setting the “initial” position during first installation. The mechanisms are delivered with the counters engaged with the other parts of the mechanism. Once installed on a valve, the counters must be reset so as to correctly indicate valve spindle positions at which keys are to be released. Generally this is achieved by removing a casing cover and manually resetting counter components, for example by rotating sprockets using a tool such as a screwdriver. It is highly undesirable to have to rely upon such manual intervention in the normal operation of the mechanism. 
     Another problem with the valve position indicator systems of known valve locks is that once they have been set during installation, they are very difficult to reset. This is a severe problem in circumstances where over time the valve spindle position corresponding to the valve being fully closed changes. Such changes often occur as the result of compression over time of valve seals. For example, in a new installation, when the valve is fully closed by applying an appropriate torque to a hand wheel actuator, the valve spindle rotates until resilient valve seals are compressed to an extent sufficient to resist that applied torque. Over time, as the valve seals age and are subjected to repeated compression and relaxation, the same applied torque could result in the valve spindle being turned several times beyond the initial “fully closed” position. Thus if the locking mechanism is not reset, a valve which is locked in the “fully closed” condition may in fact be several turns away from being fully closed. Potentially dangerous leakage can therefore occur through a valve which is nominally fully closed. 
     In a conventional valve lock, the valve spindle is interengaged with a hub of the lock mechanism such that rotation of the hub is directly coupled to the spindle. In the known devices, this interengagement is achieved by fitting a customised body between the spindle and the hub, the body defining a bore the cross-section of which is machined to match the cross-section of the valve spindle and having an outer periphery defining two slots which receive mating ribs on the hub. Such an arrangement works perfectly satisfactorily but raises two problems. Firstly, the interengaging body has to be designed to fit a particular spindle cross-section and therefore the installer has to know in advance of installation the detailed geometry of the valve spindle. As a result a detailed specification of the valve structure has to be prepared for the installer and valve locks cannot be reliably fitted without such advance information. Secondly, given that it is often the case that the valve lock must be mounted in a pre-determined orientation on the valve body, and must be interengaged with the valve spindle once the valve has been fully closed, it is sometimes necessary to partially open the valve by rotating the spindle back from its fully closed position until the spindle is in a position in which it can be inserted in the bore in the interengaging body mounted in the hub. It would be highly advantageous if a device could be provided which would enable a fitter to install a valve lock on a valve spindle without prior knowledge of the spindle geometry and without significant constraint on the relative orientation of the spindle and the valve body when the interengagement is established. 
     It is an object of the present invention to obviate or mitigate one or more of the problems outlined above. 
     According to the present invention, there is provided a valve lock for locking a valve spindle in a selected position relative to a valve body, comprising a housing which in use is mounted on the valve body, a spindle engaging member which rotates with the valve spindle relative to the housing, a latch which is actuable by a key to assume a latched condition in which rotation of the spindle engaging member relative to the housing is permitted in one direction but prevented in the other direction, and a spindle position indicator coupled by a transmission to the spindle engaging member so as to be displaced as a result of rotation of the spindle, wherein the spindle position indicator prevents actuation of the latch by the key except when the spindle position indicator is in a pre-determined orientation, the spindle position indicator is locked in the pre-determined orientation when the latch has been actuated by the key, and the transmission incorporates a slip clutch which enables rotation of the spindle engaging member in the said one direction if the spindle position indicator is locked in the pre-determined orientation and sufficient torque is applied to the spindle engaging member, whereby the selected position can be reset. 
     With valve locks in accordance with the invention, initial setting of the spindle position indicator upon installation can be readily achieved by locking the indicator and then relying upon the ratchet-like latch to enable movement of the spindle to a desired “set” position. Equally, if after prolonged use a user of such a valve lock turns the valve spindle to an extreme position and discovers that the valve lock is not operable in that extreme position, the valve can simply be rotated back to a position at which the lock can be operated, and then advanced again after the spindle position indicator has been locked in position. The spindle position indicator can then be released once the valve has reached its extreme position, the indicator thus having been reset automatically without physical intervention by the user other than a simple manipulation of the valve lock key and rotation of the valve spindle. 
     The term “slip clutch” is used herein to mean any mechanical device which can be incorporated in the transmission so as to normally faithfully transmit rotation of the spindle to displacement of the position indicator but which enables relative slippage between them when the position indicator is locked and a sufficient torque is applied to the spindle. 
     The transmission may comprise a first sprocket driven by formations supported on the spindle engaging member and a second sprocket in driving engagement with the spindle position indicator, the slip clutch being located between the first and second sprockets such that the first sprocket can rotate relative to the second if sufficient torque is applied. The second sprocket may comprise two sets of axially spaced teeth and the spindle position indicator may comprise two axially spaced coaxial sprockets meshing with respective sets of teeth, actuation of the latch being prevented unless both the first and second spindle position indicator sprockets are in pre-determined rotational positions, the number of teeth in the sets of teeth and the number of teeth in the first and second spindle position indicator sprockets being selected to prevent actuation of the latch at more than one position of the spindle. 
     Preferably the housing is provided with a viewing window through which portions of the coaxial sprockets are visible, one or more of the sprockets carrying a marker to indicate when the sprockets are in the pre-determined rotational positions. The first and second spindle position indicator sprockets may define slots which are aligned with key displaceable members only when the sprockets are in the pre-determined relative positions, the slots when so aligned permitting rotation of the key displaceable members, and rotation of the key displaceable members also causing actuation of the latch. The key displaceable members may be mounted to extend radially from a shaft which extends between two flanges in which the slots are defined, the shaft being rotatable about its major axis by the key. The shaft may bear against the latch and be shaped such that rotation of the shaft to a position in which the key displaceable members are engaged in the slots actuates the latch. The shaft may support an indicator which is visible when the shaft is rotated to the position in which the key displaceable members are engaged in the slots. 
     The slip clutch preferably comprises first and second members, surfaces of which are biased together by a spring, the surfaces being non-planar such that relative movement between them requires relative displacement between the two members and compression of the spring. The two surfaces may define mating peaks and troughs. 
     Preferably two spindle position indicators and two latches are arranged such that one latch when actuated prevents rotation of the spindle engaging member in one direction and the other latch when actuated prevents rotation of the spindle engaging member in the other direction, each spindle position indicator being coupled to the spindle engaging member by a respective transmission incorporating a respective slip clutch. This enables the valve lock to be secured at two spindle positions. 
     Preferably the spindle engaging member supports an annular array of teeth and the or each latch comprises a pivotal lever which is biased to a first position in which it engages the teeth and is moveable by the key to a second position in which it is spaced from the teeth, the lever being arranged such that when in the first position rotation of the teeth in one direction is permitted but rotation in the opposite direction is prevented as a result of the lever jamming an engagement with the teeth. A latch override member is preferably provided which may be driven into the housing to move the latch to the second position, means being provided to retain the driven member within the housing to indicate that the latch has been overridden. 
     Preferably the spindle engaging member defines a socket uniform. non-circular cross-section in planes perpendicular to an axis about which the spindle is rotatable, and the plurality of plates are engaged between the socket and spindle, each plate defining a peripheral edge which is shaped to fit the socket cross-section in each of the plurality of rotational positions relative to the spindle axis, and each plate defining an opening having a straight edge positioned relative to the plate to abut a plane surface defined by the spindle. 
     The present invention also provides a valve spindle adapter assembly comprising a housing which in use is mounted on a valve body from which extends a spindle that is rotatable relative to the valve body about a pre-determined axis, a hub mounted on the housing so as to be rotatable about the spindle axis, and means for inter-engaging the hub and the spindle such that the hub and spindle rotate together, the spindle extending into a socket defined by the hub, and the socket being of uniform non-circular cross-section in planes perpendicular to the spindle axis, wherein the means for inter-engaging the hub and spindle comprises a plurality of plates each defining a peripheral edge which is shaped to fit the socket cross-section in each of a plurality of rotational positions relative to the spindle axis. each plate defining an opening having a straight edge positioned to abut said one planar surface of the spindle. 
     With such an adapter, a limited number of different plates with identical peripheral dimensions but different opening dimensions may be supplied to enable a fitter to interengage a standard valve lock hub with a wide range of different valve spindle configurations. 
    
    
     An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a plan view of the embodiment of the invention after removal of a housing cover; 
     FIG. 2 is plan view of a housing cover which in use is mounted on the assembly as illustrated in FIG. 1; 
     FIG. 3 shows a latch which is shown in FIG. 1 in an alternative position; 
     FIG. 4 illustrates the end of a key-actuated shaft which is incorporated in the embodiment of FIG. 1; 
     FIGS. 5 to  8  illustrate the detailed structure of a transmission component of the assembly shown in FIG.  1 . 
     FIG. 9 illustrates component parts of a spindle position indicator shown in FIG.  1 . 
     FIG. 10 illustrates the inter-relationship between the spindle position indicator described with reference to FIG.  9  and the transmission described with reference to FIGS. 5 to  8 ; 
     FIG. 11 is a plan view of position indicators shown in FIG. 1 in a pre-determined configuration in which associated keys can be actuated; 
     FIG. 12 is a plan view of a plate which may be used with the arrangement shown in FIG. 1 to interengage a valve spindle and a locking mechanism hub; 
     FIG. 13 shows the use of plates as shown in FIG. 12 to interengage a hexagonal section spindle; and 
     FIG. 14 shows the use of plates as shown in FIG. 12 to interengage a square section spindle and the illustrated embodiment of the invention. 
    
    
     Referring to FIG. 1, a valve lock in accordance with the present invention is shown after removal of a cover plate which is shown in FIG.  2 . In use, the illustrated valve lock is clamped in any convenient manner to the body of a valve to be controlled (not shown) such that a spindle of the valve extends into and is engaged by the assembly. Only the spindle of the valve is shown in FIG.  1 . The valve lock comprises a housing  1  which is clamped to the valve body, an annular valve spindle engaging member or hub  2 , a transmission  3  which engages the hub  2  so as to be driven in rotation thereby, a first spindle position indicator  4  which is coupled to the transmission  3 , and a second spindle position indicator  5  which is also coupled to the transmission  3 . The indicator  4  interacts with a locking shaft  6  controlled by a key  7  and the indicator  5  interacts with a locking shaft  8  controlled by a key  9 . The mechanism is arranged such that the valve spindle can be locked in either of two pre-determined positions, one of which is determined by indicator  4  and the other of which is determined by indicator  5 . The position determined by indicator  4  corresponds in the case of the illustrated valve lock to a position in which a valve spindle  10  engaged by the illustrated assembly has been turned as far as possible in a clockwise direction so as to close the valve. The position determined by indicator  5  corresponds to the opposite case, that is the valve spindle having been turned as far as possible in the anti-clockwise direction to the fully open condition. 
     The hub  2  has an axially uniform cross-section defining a surface  11  similar to that found inside a socket of the type used for rotating a nut. Thus in cross-section the surface  11  defines twelve recesses. As described in detail below, a space  12  is thus defined between the surface  11  and the spindle  10  into which plates may be inserted to interengage the spindle  10  and hub  2 . Thus in the assembled condition, the spindle  10  and the hub  2  rotate together. 
     The outer surface of the hub  2  supports two axially spaced rings each defining twenty one teeth  13 , the teeth of one ring being aligned with the teeth of the other. Three pins  14  extend across the axial gap between the two rings of teeth  13 , the pins  14  driving the transmission  3 . Latches  15  and  16  are biased by springs  17  into engagement with the outer surface of the hub so as to define two ratchet mechanisms with the teeth  13 . In the position of the latches  15  and  16  shown in FIG. 1, the hub  2  is free to rotate in both directions. Each of the latches is pivotal from the positions shown in FIG. 1 into engagement with the adjacent teeth  13 , FIG. 3 showing the position of the latch  16  after it has been so displaced. With the latch  15  in the position shown in FIG.  1  and the latch  16  in the position shown in FIG. 3, the hub  2  could be rotated in the anti-clockwise direction but not in the clockwise direction, and vice-versa. 
     The end of the shaft  8  remote from the key  9  is supported in an upstanding plate  18  through which it projects into engagement with one end of the latch  16 . Rotation of the shaft  8  through 90° about its major axis as a result of rotation of the key  9  enables the latch  16  to move between the positions shown for that component in FIGS. 1 and 3. It will be seen from FIGS. 1 and 4 that the end of the shaft  8  defines a recess  19  which, when the shaft  8  has been rotated to the position shown in FIG. 3, is aligned with a pin  20  mounted in a tube  21  supported on the housing  1 . Thus if the shaft  8  and latch  16  are in the position shown in FIG. 3, the latch can be displaced to the position shown in FIG. 1 by driving the pin  20  into the housing. Thus, in an emergency a locked open valve can be released by driving in the pin  20  to override the locking mechanism. An indicator device  22  is mounted on the pin  20  so as to be snapped off when the pin is driven in, thereby making it possible to see when the pin  20  has been displaced. In addition, a clip  23  is retained in slots cut in the tube  21  and, in the position of the pin shown in FIG. 1, engages in a groove formed in the pin  20 . When the pin  20  is driven into the housing, the force is sufficient to cause the clip to ride up out of the groove in which it is initially engaged and then to snap back into a groove  24  formed adjacent the driven end of the pin  20 . This retains the pin  20  within the housing and makes unauthorised retraction of the pin difficult. 
     The shaft  8  supports a plate  25  which as described below is used to lock the indicator  5 . In the position of the key  9  and shaft  8  shown in FIG. 1, the plate  25  is in a position in which it does not obstruct rotation of the indicator  5 . Rotation of the shaft  8  through 90° to the position shown in FIG. 3 would however enable the plate  25  to engage in slots provided in the indicator as described below. The shaft  8  also supports an indicator lever  26  which adopts the position shown in broken lines in FIG. 1 when the key  9  is turned clockwise, and which would be visible beneath an indicator window  27  (the position of which is shown in broken lines  27  in FIG.  1  and is shown in full in FIG. 2) when the key  9  is rotated in the anti-clockwise direction. 
     The shaft  6  supports a plate  28  and indicator lever  29  and can be engaged by a release pin  30  in exactly the same manner as the shaft  8  supports the plate  25  and indicator  26  and interacts with the pin  20 . A viewing window  31  is also provided above the shaft  6 . 
     FIGS. 5 to  8  illustrate the structure of the transmission  3  of FIG. 1 The transmission comprises six components, that is a central section  32 , an upper section  33  supporting eight upper teeth  34  and nine lower teeth  35 , a lower section  36  supporting nine upper teeth  37  and eight lower teeth  38 , upper and lower cam members  39  and  40  which are slidably received within the central section  32 , and a compression spring  41  which is located within the central section  32  and biases the cam members  39  and  40  apart. The cam members  39  and  40  are hexagonal to fit within a hexagonal passage within the central section  32  and each define ramp surfaces  42  which mate with ramp surfaces  43  defined on the upper and lower sections  33  and  36  respectively. Each of the ramp surfaces defines three peaks separated by troughs such that for example components  33  and  39  normally assume one of three relative orientations. 
     The central section  32  supports a sprocket  44  which engages with the pins  14  (FIG.  1 ). The sprocket  44  of the central section comprises nine teeth. Generally the central section  32  and the end sections  33  and  36  rotate as a single body. Thus a single rotation of the hub  2  of FIG. 1 drives the three pins  14  past the transmission, causing the central section  32  to rotate through 120°. This causes the teeth  34 ,  35 ,  37  and  38  to advance through 120°. 
     The structure of the spindle position indicator  4  is shown in FIG.  9 . The structure of the spindle position indicator  5  of FIG. 1 is identical to that illustrated in FIG. 9 except for the fact that the mechanism is inverted. FIG. 10 shows the inter-relationship between the transmission  3  and the position indicators  4  and  5 . 
     Referring to FIG. 9, each of the position indicators comprises a shaft  45  supporting a nine-tooth sprocket  46  which is secured to a member  47  so as to rotate therewith. The member  47  defines a radially extending flange  48 . Journalled on the shaft  45  is a central sprocket assembly comprising an eight-tooth sprocket  49  and a radially extending flange  50 . In the assembled condition of the spindle position indicator a space is defined between the flanges  48  and  50 , that space accommodating the sprocket  44  of the transmission assembly. The space defined between the sprockets  48  and  50  also receives the shaft  6  or  8  of the key actuated assembly. 
     As can best be seen from FIG. 11 which represents a plan view of the two position indicators  4  and  5  of FIG. 1, the flanges  48  and  50  define slots  51  and  52  which in a single pre-determined orientation of the slots  51  and  52  are aligned with the plates  28  and  25  mounted on the shafts  6  and  8 . The plates are dimensioned such that when they project perpendicular to the planes defined by the flanges  48  and  50 , as illustrated in the case of indicator  4  in FIG. 11, they project into the slots  51  and  52 , thereby preventing rotation of flanges  48  and  50  and the sprockets  46  and  49 . Rotation of the shaft  8  through 90° would cause the plate  25  to assume the position shown in FIG. 11 in the case of the indicator  5  where the plate  25  is received wholly in the space defined between the flanges  48  and  50 . Thus with the plate  25  in the orientation shown for indicator  5  in FIG. 11, the flanges  48  and  50  of indicator  5  are free to rotate. It will be appreciated that whereas in FIG. 11 both of the indicators are shown in a configuration in which they may be locked in position, in practice this would not normally be the case as the indicator  4  could only be locked in position with the valve fully closed and the indicator  5  could only be locked in position with the valve fully open. 
     The valve lock described with reference to FIGS. 1 to  11  can be readily mounted on a valve so as to enable that valve to be locked in both fully open and fully closed position. The assembly would normally be delivered with both of the indicators  4  and  5  locked, that is with the indicator  4  and  5  in the position shown in FIG. 11 but with the shaft  8  rotated through 90° as compared with the position shown in FIG.  11 . Once installed, this relative configuration of the two indicators would not occur again. Prior to mounting the assembly on a valve, the valve spindle would be fully closed by turning the spindle as far as possible in a clockwise direction. The housing  1  would then be clamped to the valve body, the hub  2  would be interengaged with the spindle  10  as described in detail below, and the key  7  would be rotated to the position shown in FIG. 1 to enable anti-clockwise rotation of the hub  2 . 
     The hub  2  would then be rotated until the valve was in the fully open position, the latch  16  and the teeth  13  operating in the manner of a ratchet and pawl. Rotation of the hub  2  in the anti-clockwise direction drives the transmission  3  which in turn drives the indicator  4 . Thus the movements of the components of the indicator  4  track those of the hub  2 . The indicator  5  remains locked however and one of the clutch mechanisms in the transmission  3  enables the sprocket  44  to rotate without rotating the indicator  5 . Once the valve is fully open, the key  9  can be turned, any subsequent rotation of the hub then being tracked by both indicator  4  and indicator  5 . 
     With the mechanism set as described above, with the keys in the position shown in FIG. 1 the valve can be opened or closed at will. If it is desired to lock the valve in the fully closed position, the spindle is rotated as far as possible in a clockwise direction, thereby returning the left hand indicator  4  to its initial condition in which the shaft  6  can be rotated to lock the flanges  48  and  50  together. Rotation of the shaft also causes the latch  15  to engage, thereby preventing anti-clockwise rotation of the spindle to reopen the valve. Similarly, if it is desired to lock the valve in the open position, this can be achieved by fully opening the valve and then turning the key  9 . The keys  7  and  9  are captive except when the associated shaft  6  or  8  has been rotated to engage the respective latch  15  or  16 . 
     The levers  26  and  29  are visible through the windows  27  and  31  and thereby enable a user to readily identify whether or not the shafts  6  and  8  have been rotated to the locked condition. Similarly, one or both of the sprockets  46  and  49  of indicator  4  can carry for example a fluorescent or other visible marker to indicate when the slots  51  and  52  have been aligned to enable rotation of the shaft  6 . A marker or markers may also be provided on the flange  48  of indicator  5  for a similar reason. Thus in the event of a user being unable to turn the key when it is believed that the valve is in the position in which it should be locked, the relative positions of the position indicators  4  and  5  can be easily checked. 
     It is often the case that after a period of use the seals of a valve become compressed or worn such that whereas initially a pre-set number of rotations of the spindle from a valve fully open position was sufficient to fully close the valve, further turns are now necessary. In such circumstances locking the valve in the position which initially corresponded to the fully closed condition would not ensure that the valve was sealed. The described assembly enables this serious problem to be overcome by allowing the user to reset the “fully locked” spindle position to take account of such valve compression. 
     If a user fully closes a valve and finds that the key  7  cannot be turned, and confirms that this is because the spindle has been rotated beyond the initial “fully closed” spindle setting, that setting can be adjusted by locking the position indicator  4  when the slots  51  are aligned before the valve is fully closed and then closing the valve fully whilst the latch  16  is in the position shown in FIG.  1 . The latch  15  then simply rides over the teeth  13  until the valve has been fully closed. The setting of the position indicator  5  is not disrupted as that position indicator rotates with the hub  2 , but the setting of the indicator  4  is effectively reset as necessary. Thus the valve lock is readily reset without requiring any tools and without requiring any operator skill other than a simple appreciation that if the indicator  4  can only be locked before the valve is fully closed, it should be locked in whatever position is possible and then the valve should be fully closed to reset the indicator. 
     Referring to FIG. 12, this is a simple plan view of a plate  53  which may be used to interengage the hub  2  and spindle  10  of FIG.  1 . The plate is in the form of a simple sheet of steel into which a slot  54  has been cut with arcuate end edges  55  and parallel side edges  56 . The peripheral edge  57  of the plate is hexagonal and may therefore be positioned in one of twelve positions relative to the hub  2  of FIG.  1 . Thus assuming that the housing  1  of FIG. 1 has been mounted on a valve body and the spindle has been rotated to the valve fully closed position as described above in accordance with the standard fitting procedure, the spindle  10  will adopt a rotational position relative to the hub  2  which cannot be accurately predicted. A plate  53  as shown in FIG. 12 in which the edges  56  are spaced by the distance between the opposed faces of the hexagonal spindle shaft may however be placed in the socket defined by the hub  2  in any one of twelve orientations and therefore the hub  2  and spindle  10  may be readily interengaged in a position which at most requires relative rotation between the spindle and the shaft of {fraction (1/24)} of a full revolution, that is 15°. Subsequent plates can then be dropped in with different orientations such that each of the three pair of faces of the hexagon abut the edges  56  of at least one plate. FIG. 13 shows such an arrangement with the topmost plate  53  being shown in full lines covered edges of the slots  54  in two lower plates being shown in dotted lines. Thus, providing a sufficiently high stack of plates is inserted into the socket defined by the hub  2 , a very secure interconnection can be achieved between the spindle and the hub. 
     The dimensions of a spindle may not be known in advance. However, a relatively limited range of plates  54  will be sufficient to enable all spindle shapes and sizes to be accommodated. The only variable that would be of relevance would be the spacing between the edges  56 . A fitter provided with a stock of plates with a range of sizes in terms of the spacing between the edges  56  would be able to accommodate any hexagonal spindle. Similarly, if other spindle shapes were encountered, for example a square spindle as shown in FIG. 14, the same set of plates  53  with different spacings between the edges  56  can be used to interengage the spindle  10  and the hub  2 . 
     It will be appreciated that although the described embodiment is adapted to lock a valve in a fully opened or a fully closed position, a single latch, transmission and position indicator could be provided to lock a valve in only one of its extreme positions. Furthermore, the illustrated arrangement could be set up to lock a valve in one extreme position and an intermediate position in which for example the valve is half open. This could be achieved by removing the latching mechanism provided for locking in one extreme position, and extending one or both of the slots in the two parts of the associated position indicator mechanism. With such modifications, the device would still enable ready resetting of the extreme position in which the valve can be locked shut. 
     It will also be appreciated that a further key operated lock mechanism could be provided on the side of the housing remote from the two keys of the illustrated embodiment so as to directly engage the hub. With such an arrangement a supervisor could for example prevent any manipulation of the valve spindle. 
     It will be appreciated that the housing could incorporate sensing devices capable of generating an electrical signal indicative of the valve lock condition to enable the signalling of that condition to a remote location.