Slurry valves normally include a valve body in which a valve element is located. The valve element locates on a valve seat to selectively shut off or allow flow through the body. The valve element is coupled to a stem which is driven to raise and lower the valve element towards and away from the seat. As material flows through the valve, scale can build up on the valve seat and when it is desired to close the valve, the valve is stopped from completely closing by the build-up of the scale.

Conventional slurry valves of the above type have a torque converter for enabling the valve stem to raise and lower to open and close the valve and a sledge jam nut arrangement.

A gear or handle is connected to the valve stem so that when it is desired to grind scale from the valve seat the torque converter is released by removing a pin from the torque converter and unlocking the sledge jam nut by hitting with a sledge hammer. The handle is then hit moved manually or with a sledge hammer to cause rotation of the valve stem so that the valve element grinds against the seat to remove scale from the valve seat. In larger valves the gear is used to drive the valve element to remove the scale.

This grinding operation is manually intensive and also in view of the need to use a heavy object such as a sledge hammer can result in damage to the valve or the person operating the valve.

The object of the present invention is to provide a valve in which grinding can occur but which is less manually intensive and does not require the use of a sledge hammer

to enable the grinding operation.

The invention may be said to reside in a valve including ; a valve body having an inlet and an outlet ; a valve seat in the valve body ; a valve element for seating against the valve seat; a valve stem coupled to the valve element ; first drive means for rotating the valve stem to cause the valve stem to move in the longitudinal direction of the stem to move the valve element to selectively seat against the valve seat to close the valve or move away from the valve seat to open the valve ; second drive means for providing drive to the valve stem ; and actuating means for selectively operating the second drive means in combination with the first drive means to cause the valve element to perform a grinding operation to grind scale build-up off the valve seat.

Thus, according to present invention in order to grind scale from the valve seat it is only necessary to selectively operate the second drive means in combination with the first drive means to cause the grinding operation to occur.

Preferably the second drive means causes the valve stem to rotate with little or no longitudinal movement of the valve stem so that the rotation of the valve stem without the longitudinal movement enables the valve element to perform the grinding operation on the valve seat.

Preferably the first drive means comprises a first spur gear coupled to the valve stem for rotating the valve stem and for allowing the valve stem to move in a longitudinal direction of the valve stem relative to the first spur gear.

Preferably the first drive means further includes a first pinion gear mounted on a shaft, the first pinion gear meshing with the first spur gear so that an actuator can rotate the shaft to rotate the first pinion gear and first spur gear to supply drive to rotate the valve stem.

Preferably the valve stem extends through a screw threaded yoke bush, the stem having a screw thread which engages the screw threads in the yoke bush so that when the stem is rotated by the first drive means, relative to the yoke bush the engagement between the screw thread on the stem and the screw thread in the yoke bush causes the stem to move in the longitudinal direction of the stem.

Preferably the second drive means comprises a second spur gear coupled to the yoke bush for rotating the yoke bush at the same speed as the first drive means rotates the stem so that the combined effect of the rotation of the first spur gear and rotation of the second spur gear causes the valve stem to rotate without movement of the valve stem in the longitudinal direction of the valve stem.

Preferably the second drive means further includes a second pinion gear engaged with the second spur gear.

Preferably the actuating means comprises releasable locking means for locking the spur gear and selectively releasing the spur gear for rotation to rotate the yoke bush.

In one embodiment the releasable locking means comprises a key on the second pinion gear for cooperating with a fixed cooperating key component so as to hold the second pinion gear fixed at a first position to thereby hold the second spur gear fixed and the second pinion gear being moveable to a second position to remove the key from the fixed cooperating key component to release the second spur gear

for rotation to impart rotation to the second spur gear.

Preferably the shaft has a second cooperating key component for engagement with the key on the second pinion gear for locking the second pinion gear to the shaft for rotation with the shaft when the second pinion gear is in the second position.

Preferably the second pinion gear is slideable from the first position in which it is fixed stationary to the second position where it is engaged with the shaft for rotation with the shaft whilst at all times being in mesh with the second spur gear.

In one embodiment the first and second pinion gears are provided on a common shaft. However, in another embodiment the first and second pinion gears are provided on separate shafts.

In another embodiment of the invention the locking means comprises a locking pinion gear in mesh with the second spur gear and/or second pinion gear.

In this embodiment the locking pinion gear has a locking profile coupled to the locking pinion gear for receipt in a fixed locking recess, the locking profile being engagable in a first position in the locking recess to lock the second spur gear and therefore the second pinion gear, and the locking pinion gear and locking profile being moveable to a second position to release the locking profile from the locking recess to enable rotation of the second spur gear and therefore allow the second pinion gear to drive the second spur gear.

Preferably the locking pinion gear has a locking shaft and the locking profile is provided on the locking shaft, the locking pinion and locking shaft being slidable from the

first position to the second position.

Preferably the shaft or shafts have an engagement head for engagement with a tool to rotate the shaft or shafts to impart rotation to the first and second pinion gears and hence to the first and second spur gears.

Preferably the locking profile is of hexagon shape.

However other shapes could be used.

In one embodiment of the invention a gear box is provided for engaging the shafts carrying the first and second pinion gears and for transmitting drive to the first and second shafts.

In one embodiment of the invention the first and second spur gears can be driven at a different drive ratio so as to cause the valve stem to move in the longitudinal direction of the valve stem at very slow speed compared to the rotational speed of the valve stem so that a grinding operation can be performed as the valve stem closes the valve element against the valve seat in view of the slow longitudinal movement of the valve stem and the relatively high rotational speed of the valve stem and valve element.

The invention in a further aspect may also be said to reside in a valve including ; a valve body having an inlet and an outlet; a valve seat in the valve body; a valve element for seating against the valve seat; a valve stem coupled to the valve element; first drive means for rotating the valve stem to cause the valve stem to move in the longitudinal direction of the stem to move the valve element to selectively seat against the valve seat to close the valve or move away from the valve seat to open the valve; and

second drive means for providing drive to the valve stem so that when the first drive means rotates the stem the second drive means provides a counter drive to prevent longitudinal movement of the valve stem so that the valve stem rotates but does not move longitudinally so that the rotation of the stem and therefore the rotation of the valve element can grind scale build up off the valve seat.

Once again, according to this aspect of the invention it is only necessary to operate the two drive means in order to grind scale from the valve seat.

Preferably the second drive means causes the valve stem to rotate with little or no longitudinal movement of the valve stem so that the rotation of the valve stem without the longitudinal movement enables the valve element to perform the grinding operation on the valve seat.

Preferably the first drive means comprises a first spur gear coupled to the valve stem for rotating the valve stem but for allowing the valve stem to move in a longitudinal direction of the valve stem relative to the first spur gear.

Preferably the first drive means further includes a first pinion gear mounted on a shaft, the first pinion gear meshing with the first spur gear so that an actuator can rotate the shaft to rotate the first pinion gear and first spur gear to supply drive to rotate the valve stem.

Preferably the valve stem extends through a screw threaded yoke bush, the stem having a screw thread which engages the screw threads in the yoke bush so that when the stem is rotated by the first drive means, relative to the yoke bush the engagement between the screw thread on the stem and the screw thread in the yoke bush causes the stem to move in the longitudinal direction of the stem.

Preferably the second drive means comprises a second spur gear coupled to the yoke bush for rotating the yoke bush at the same speed as the first drive means rotates the stem so that the combined effect of the rotation of the first spur gear and rotation of the second spur gear causes the valve stem to rotate without movement of the valve stem in the longitudinal direction of the valve stem.

Preferably the second drive means further includes a second pinion gear engaged with the second spur gear.

Preferably the actuating means comprises releasable locking means for locking the spur gear and selectively releasing the spur gear for rotation to rotate the yoke bush.

In one embodiment the releasable locking means comprises a key on the second pinion gear for cooperating with a fixed cooperating key component so as to hold the second pinion gear fixed at a first position to thereby hold the second spur gear fixed and the second pinion gear being moveable to a second position to remove the key from the fixed cooperating key component to release the second spur gear for rotation to impart rotation to the second spur gear.

Preferably the shaft has a second cooperating key component for engagement with the key on the second pinion gear for locking the second pinion gear to the shaft for rotation with the shaft when the second pinion gear is in the second position.

Preferably the second pinion gear is slideable from the first position in which it is fixed stationary to the second position where it is engaged with the shaft for rotation with the shaft whilst at all times being in mesh with the second spur gear.

In another embodiment of the invention the locking means comprises a locking pinion gear in mesh with the second spur gear and/or second pinion gear.

In this embodiment the locking pinion gear has a locking profile coupled to the locking pinion gear for receipt in a fixed locking recess, the locking profile being engagable in a first position in the locking recess to lock the second pinion gear and therefore the second spur gear and the second pinion gear, and the locking pinion gear and locking profile being moveable to a second position to release the locking profile from the locking recess to enable rotation of the second pinion gear and therefore the second spur gear.

Preferably the locking pinion gear has a locking shaft and the locking profile is provided on the locking shaft, the locking pinion and locking shaft being slidable from the first position to the second position.

Preferably the shaft or shafts have an engagement head for engagement with a tool to rotate the shaft or shafts to impart rotation to the first and second pinion gears and hence to the first and second spur gears.

Preferably the locking profile is of hexagon shape.

A further aspect of the invention may be said to reside in a valve including a valve body having an inlet and an outlet ; a valve seat in the valve body ; a valve element for seating against the valve seat ; a valve stem coupled to the valve element, the valve stem having a screw thread ; a valve stem engaging member having a screw thread for engaging the screw thread on the valve stem ;

first drive means for rotating the valve stem to cause the valve stem to move in the longitudinal direction of the stem because of the screw threaded engagement between the valve stem and the engagement member to move the valve element to selectively seat against the valve seat to close the valve or move away from the valve seat to open valve ; and valve seat grinding means for rotating the engagement member to decrease the rate of movement of the valve stem and therefore the valve member towards the valve seat so that rotation of the valve stem and valve member and the decreased rate of movement of the valve stem and member causes grinding of the valve member against the valve seat.

Preferably the engaging member comprises a yoke bush through which the valve stem passes, the screw thread on the engaging member being an internal screw thread in the yoke bush and the screw thread on the valve stem being an external screw thread on the valve stem for engagement with the screw thread in the yoke bush.

In one embodiment the grinding means rotates the engaging member at the same speed as the first drive means rotates the valve stem so that the valve stem does not move in a longitudinal direction of the valve stem but rotates so that the valve member can grind against the valve seat to grind scale build up off the valve seat.

However, in other embodiments the grinding means may drive the engagement member at a speed different to the speed of rotation of the valve stem so that the valve stem and therefore the valve member are caused to move slowly towards the valve seat whilst rotating at a relatively higher speed compared to the downward movement of the valve stem so that as the valve member closes against the valve seat the valve member grinds against the valve seat to

grind scale build up off the valve seat.

Preferably the grinding means comprises a second spur gear coupled to the yoke bush for rotating the yoke bush, the second spur gear being in mesh with a second pinion gear provided on a shaft such that when the shaft is rotated the second pinion gear is rotated to drive the second spur gear to rotate the yoke bush.

Preferably the first drive means comprises a first spur gear coupled to the valve stem for rotating the valve stem but for allowing the valve stem to move in a longitudinal direction of the valve stem relative to the first spur gear.

Preferably the first drive means further includes a first pinion gear mounted on a shaft, the first pinion gear meshing with the first spur gear so that an actuator can rotate the shaft to rotate the first pinion gear and first spur gear to supply drive to rotate the valve stem.

Preferably the grinding means includes releasable locking means for actuating the grinding means.

In one embodiment the releasable locking means comprises a key on the second pinion gear for cooperating with a fixed cooperating key component so as to hold the second pinion gear fixed at a first position to thereby hold the second spur gear fixed and the second pinion gear being moveable to a second position to remove the key from the fixed cooperating key component to release the second spur gear for rotation to impart rotation to the second spur gear.

Preferably the shaft has a second cooperating key component for engagement with the key on the second pinion gear for locking the second pinion gear to the shaft for rotation with the shaft when the second pinion gear is in the second

position.

Preferably the second pinion gear is slideable from the first position in which it is fixed stationary to the second position where it is engaged with the shaft for rotation with the shaft whilst at all times being in mesh with the second spur gear.

In another embodiment of the invention the locking means comprises a locking pinion gear in mesh with the second spur gear and/or second pinion gear.

In this embodiment the locking pinion gear has a locking profile coupled to the locking pinion gear for receipt in a fixed locking recess, the locking profile being engagable in a first position in the locking recess to lock the second spur gear and therefore the second pinion gear, and the locking pinion gear and locking profile being moveable to a second position to release the locking profile from the locking recess to enable rotation of the second spur gear and therefore allow the second pinion gear to drive the second spur gear.

Preferably the locking pinion gear has a locking shaft and the locking profile is provided on the locking shaft, the locking pinion and locking shaft being slidable from the first position to the second position.

In one embodiment of the invention the first and second pinion gears have motors which directly drive the first and second pinion gears or are engaged with the shafts on which the pinion gears are mounted, actuation of the motors driving the pinion gears to drive the spur gears.

In other embodiments, the first spur gear may be replaced by a drive motor which can be a hydraulic motor, electric motor or a pneumatic motor for directly driving the valve

stem for rotation to move the valve stem and the valve element in the longitudinal direction of the valve stem to open and close the valve.

In this embodiment a further motor could be engaged with the shaft carrying the second pinion gear for driving the second pinion gear and therefore the second spur gear or holding the second pinion gear and therefore the second spur gear stationary.

In this embodiment the motors may be operated from a remote location via wiring, hydraulic or pneumatic piping so as to operate the valve from a remote location. This has particular application to the operation of the valve which may be installed in difficult to reach locations such as in wells, holes, trenches or the like. Preferably the cables are connected to a control box having switches for operating the motors to open and close the valve and also to perform the grinding operation.

A further aspect of the invention relates to a gear box for supplying drive to cause grinding of the valve element against the valve seat to remove scale build up on the valve seat.

This aspect of the invention may be said to reside in a gear box for use with a valve which has a valve stem, a valve element for seating on a valve seat, a first spur gear for rotating the valve stem, a second spur gear for providing counter drive so that the longitudinal movement of the stem is slowed down or completely prevented, the first spur gear having a meshing first pinion gear provided on a first shaft and the second spur gear having a meshing second pinion gear provided on a second shaft, the first and second shafts having engagement portions, said gear box including ; an input shaft for receiving input rotary power,

the input shaft having a first gear; second and third gears for driving by the first gear; second and third shafts mounted on the second and third gears, complementary engagement heads on the second and third shafts for engagement with the engagement heads on the first and second pinion shafts; and wherein when the complementary engagement heads are engaged with engagement heads on the first and second pinion shafts and drive is supplied to the first shaft the second and third shafts are driven to supply drive to the first and second pinion shafts to inturn supply drive to the first and second spur gears.

In one embodiment of the invention a locking pinion gear is provided on a locking shaft, the shaft being moveable from a first position in which the locking pinion gear enables rotation of the second pinion gear and second spur gear to a second position in which the locking shaft is locked against rotation and the locking pinion gear is in mesh with the second pinion gear and/or the second spur gear to lock the second spur gear against rotation; and said gear box having a locking pinion shaft engagement member for engaging the locking shaft when the complimentary engagement heads are located in engagement with the engagement heads of the first and second pinion shafts so that the member moves the locking shaft from the second position to the first position to enable rotation of the second pinion gear and the second spur gear.

Preferably the engagement member comprises an engagement pin for abutting an end of the locking shaft and pushing the locking shaft from the second position to the first position.

Preferably the locking shaft has a locking profile which is engagable in a locking recess for locking the locking shaft

against rotation.

Preferably the locking profile is of hexagon shape.

Preferred embodiments of the invention will be described, by way of example with reference to the accompanying drawings in which; Figure 1 is cross-sectional view through a valve according to one embodiment of the invention; Figures 1A, 1B, IC and 1D are cross-sectional views along the lines 1A-1A, 1B-lB, 1C-1C and iD-1D respectively shown on Figure 1; Figure 2 is view similar to Figure 1 but with the valve in a second condition for performing a grinding operation; Figure 3 is a view of a valve according to a second embodiment of the invention; Figure 4 is a view similar to Figure 3 but with the valve in a second condition for performing a grinding operation; Figure 5 is cross-sectional view through a gear box used in one embodiment of the invention; Figure 6 is view along the line A-A of Figure 5; and Figure 7 is a view of a valve according to the second embodiment showing the gear box of Figure 5 in place.

Figure 1 shows a cross-sectional view through a valve embodying in the invention. The valve includes a valve body 10 which has an inlet 12 and an outlet 14. A yoke 16 is connected to the valve body 10. A valve stem 18 is arranged within the yoke 16 and extends through an opening 20 in the valve body 10. The valve stem 18 carries a valve disc 22 at its lower end. The valve disc 22 can be secured to the stem 18 by a nut 24. The body 10 has a valve seat 26. The valve seat 26 is in the form of a annulus which

defines the opening 12 and is connected to the remainder of the valve body 10 in any suitable manner. In alternative embodiments the seat 26 can be formed integral with the remainder of the valve body 10. The stem 18 is secured in the opening 20 in the body 10 by packing rings 28 which are retained in place by a gland nut 30. The rings 28 form a seal to prevent fluid passing from the interior of the valve body 10 into the yoke 16.

The yoke 16 has a retainer cap 30 at its upper end which has an opening 32. The yoke 16 also has an internally projecting shoulder 34. A yoke bush 36 is provided in the yoke 16 about the stem 18 and extends through the opening 32. As clearly shown in Figure 1 the stem 18 passes all the way through the bush 36 and has an end portion 38 which projects out of the bush 36. Seals 39 are provided to seal the bush 36 to the yoke 16 and thrust bearings 40 are provided on both sides of the shoulder 36. The lower bearing 40 shown in Figure 1 is retained by a ledge 41 formed in the yoke 16 and the upper bearing 40 is retained by the retainer cap 30. The bearings 40 provide thrust bearings for taking the reaction of the valve stem 18 when the valve stem 18 is driven to open and close the valve disc 22 as will be explained in more detail hereinafter.

The opening 32 also has a bearing 44 for supporting the bush 36 for rotation relative to the retainer cap 30 as will be described in more detail hereinafter.

The yoke bush 36 has an internal screw thread 46 which engages with an external screw thread 48 on the stem 18.

The valve stem 18 has key slots 50 (only one shown in Figure 1) which are best seen in Figure 1A. A first spur gear 52 is provided on the stem 18 and engaged with the stem 18 by engaging the stem 18 with internal opening 54 of the spur gear 52. The internal opening 54 has key openings 51 into which keys 51a are fixed and which engage the key

slots 50 so as to fix the gear 52 onto the stem 18 so that when the gear 52 rotates, rotation is supplied to the stem 18. The stem 18 is able to move in the longitudinal direction shown by double headed arrow A in Figure 1 relative to the gear 52 by sliding of the keys 51a in the key slots 50.

The yoke bush 32 also has key slots 56 in its outer periphery and a second spur gear 58 which has an opening 60 is provided on the bush 32 by engaging the key way slots 56 with keys 61 provided in the opening 56 of the second spur gear 58.

The spur gear 52 and spur gear 58 are separated by a bearing 66.

The retainer cap 30 supports a hollow sleeve 70 which can be secured to the retainer cap 30 by welding or any suitable fashion. The sleeve 70 receives a shaft 72 which has a hexagonal head 74. A bearing or bush 76 is provided between the shaft 72 and the sleeve 70. The shaft 72 has a first pinion gear 80 which is supported on a large diameter portion 82 of the shaft 72. A retaining washer 84 is provided for retaining the pinion gear 80 in place. The washer 84 also assists in holding spur gear 52 in place.

The pinion gear 80 has teeth 86 which mesh with teeth 88 of the first spur gear 52. The end of the shaft 72 adjacent the pinion gear 80 is also provided with a hexagonal head 90.

A second slideable pinion gear 92 is also mounted on the shaft 72. In the position shown in Figure 1 the second pinion gear 92 is in a locking position in which it is keyed to the retaining cap 30 or sleeve 70 by keys 94 fixed into key slots 95 (best seen in Figure 1D) sleeve 70 or cap 30. The keys 94 locate in key slots 110 in the periphery of opening 93 through the gear 92 so as to lock the gear 92

in a fixed position so it will not rotate with the shaft 72. Thus the shaft 72 can rotate relative to gear 92 in the opening 93 through the gear 92.

As is shown in Figure 1 the second pinion gear 92 is shown lowered slightly with respect to the second spur gear 58 but nevertheless teeth 98 of the second pinion gear 92 are still in mesh with teeth 100 of the second spur gear 58.

That is, the gears 92 and 58 as shown in Figure 1 are overlapped and not in complete alignment with one another but nevertheless the engagement of part of the teeth 98 with part of the teeth 100 will lock the second spur gear 58 fixed so that it cannot rotate whilst the gear 92 is in the locked position provided by engagement of the key 94 with the key slot 95 on the sleeve 70 or cap 30.

In order to operate the valve to open and close the valve disc 22, to enable flow through the inlet 12 and out of the outlet 14, the shaft 72 is rotated by engaging a suitable tool (not shown) with one of the hexagonal heads 74 or 90 and operating the tool so as to rotate the shaft 72. The tool can be in the form of a drill or the like which is provided with a special adaptor head which is known in this field. Rotation of the shaft 72 will rotate the first pinion gear 80 which, because of the engagement of the teeth 86 and 88, will rotate the first spur gear 52.

Rotation of the first spur gear 52 will be imparted to the stem 18 by virtue of the engagement of gear 52 with the stem 18 provided by the key slots 50 and 51 and the key 51a. When the stem 18 is rotated the rotation of the stem 18 will cause the stem 18 to raise or lower in the direction of double headed arrow A by virtue of the screw thread engagement provided by the screw threads 58 and 56.

The movement of the stem 18 relative to the gear 52 is accommodated by the key connection of the gear 52 to the stem 18 so that the stem 18 can raise and lower relative to the gear 52 whilst been rotated by the gear 52. Thus, by

rotating the shaft 72 in one direction the stem 18 can be caused to rise to open the valve and by rotating the shaft 72 in the opposite direction the stem 18 can lower to close the valve.

During opening and closing of the valve disc 22 in the manner described above, the yoke bush 36 is held stationary by the spur gear 58 and the locked pinion gear 92 so that the yoke bush effectively provides a reaction for rotation of the stem 18 so that the screw thread engagement between the stem 18 and the yoke bush 36 will cause a stem 18 to move in the longitudinal direction shown by double headed arrow A relative to the yoke bush 36.

When it is desired to grind scale from the valve seat 26 the valve disc 22 is moved to the closed position so that it is abutting or pushed hard as possible against any scale which has built up on the seat 26. The second pinion gear 92 is moved from the position shown in Figure 1 to the position shown in Figure 2. As shown in Figure 2 the second pinion gear 92 has been moved by sliding the pinion gear 92 upwardly so that it now is in full engagement with the second spur gear 58. The key slots 110 have now been removed from engagement with the keys 95. The key slots 110 now move into engagement with keys 111 fixed in slots 113 provided on the periphery of the shaft 72. When the keys 111 are engaged in the slots 110 the second pinion gear 92 is fixed onto the shaft 72 for rotation with the shaft 72. Thus, when the shaft 72 is rotated drive is supplied from the second pinion gear 92 to the second spur gear 58 which in turn rotates the yoke bush 36 by virtue of the engagement of the gear 58 with the yoke bush 36.

Rotation of the yoke bush 36 provides a rotation to counter the upward or downward drive provided by the screw thread engagement of the stem 18 with the yoke bush 36. Thus, rather than the stem 18 raising or lowering under the influence of the rotation of the first spur gear 52 the

rotation of the second spur gear 58 causes the stem 18 to simply remain in the same vertical position but nevertheless rotate about its longitudinal axis so that the valve disc 22 rotates on the seat 26 to grind the seat 26 and therefore remove any scale which has built up on the seat 26.

When it is again desired to return the valve to the orientation in which it allows opening and closing of the valve disc 22 the second pinion gear 92 is simply moved from the position shown in Figure 2 back to the position shown in Figure 1 where it is released from the shaft 72 and locks onto the key 94 in the sleeve 70 or retainer cap 30. This will again lock the second spur gear 58 stationary and rotation of the shaft 72 will rotate the stem 18 within the stationary bush 36 thereby causing the stem 18 to raise or lower to open and close the valve disc 22.

In the embodiment described with reference to Figures 1 and 2, the gear ratio between the first pinion 80 and first spur gear 88 and the gear ratio between the second pinion gear 92 and second spur gear 58 are the same so that when the valve is in the orientation shown in Figure 2 the bush 36 and stem 18 are driven at the same rational speed so that the stem 18 remains in the same vertical position and does not raise or lower in its longitudinal direction.

However, it would be possible to provide a different gear ratio between the second spur gear 58 and second pinion gear 92 compared to that between the first spur gear 52 and first pinion gear 80 so that when drive is supplied from the pinion gear 92 to the gear 58 some upward or downward movement of the stem 18 is provided. If this is the case the upward and downward movement of the stem 18 will be greatly reduced in speed compared to that which occurs when the second spur gear 58 is locked fixed. Thus, the downward motion can be very slow whilst the rotation of the

stem 18 is quite high so that the valve disc 22 performs a grinding operation as it moves down and seats on the valve seat 26 because of the slow downward movement of the stem 18 and therefore valve disc 22 and the rotation of the stem 18 and valve disc 22. Obviously, the difference in ratio can be obtained by simply changing the number of teeth on the gear 58 so that it, for example, has one less tooth than the number of teeth on the spur gear 52.

In the preferred embodiment of the invention the pinion gear 92 is a generally tight fit on the shaft 72 and its respective keys so that friction will hold the spur gear 92 in the position shown in Figure 2 in engagement with the second spur gear 58. However, in other embodiments spring biased ball and detent arrangements (not shown) could also be provided to hold the gear 92 in the upper position shown in Figure 2 should that be necessary.

Figures 3,4 and 7 show a second embodiment of the invention which is generally the same as the embodiment shown in Figure 1 and Figure 2 and in which like reference numerals indicate like parts. However, in this embodiment the first pinion gear 80 and the second pinion gear 92 are provided on separate shafts 120 and 122. The shafts 120 and 122 both have hexagonal heads 74.

In this embodiment the pinion gears 80 and 92 are in permanent full engagement with their respective spur gears 52 and 58. A locking pinion 128 is provided on a shaft 130. The shaft 130 projects through a hexagonal hole 134 provided in retaining cap 30. The shaft 130 has a hexagonal shaped profile 136 about part of its periphery which matches the hexagonal hole 134 provided through the retaining cap 30. The shaft 130 also carries a lower retaining washer or O-ring 140.

When the hexagonal profile 136 is engaged within the

hexagonal hole 134 the shaft 130 is locked fixed and cannot rotate. Since the locking pinion gear 128 is in mesh with the second spur gear 58 or the second pinion gear 92 the spur gear 58 is locked in position and therefore cannot rotate. Thus, opening and closing of the valve can be performed in the same manner as described with reference to Figures 1 and 2 by rotating the shaft 120 so that the first pinion 80 rotates the first spur gear 52 to drive the stem 18 upwardly and downwardly in Figure 3 to open and close the valve disc 22.

When it is desired to perform a grinding operation the shaft 130 is pushed upwardly as shown in Figure 4 in the direction of arrow B so that the hexagonal profile 136 is removed from the hexagonal hole 134 and with the O-ring or washer 140 abutting the retainer cap 30 about the periphery of the hole 134 as shown in Figure 4. Thus, the shaft 130 is no longer locked fixed and can rotate about its longitudinal axis. Thus, when drive is supplied to the second shaft 122 the second pinion gear 92 can rotate to inturn rotate the second spur gear 58. As shown in Figure 2 the locking pinion 128 is still partially in mesh with the pinion gear 92 or the spur gear 58 so that it will just freely rotate in engagement with those gears. The rotation of the spur 58 will cause the yoke bush 36 to rotate as in the previous embodiment so as to prevent upward and downward movement of the valve stem 18 and thereby enable the valve disc 22 to perform a grinding operation on the seat 26.

Figures 5 and 6 show a gear box arrangement for use with the embodiment of Figures 3,4 and 7. With reference to Figures 5 and 6 the gear box has an outer casing 150 which supports input shaft 152. The input shaft 152 carries a gear 154. The shaft 152 may be secured in place by retainer washers 156. The shaft 152 has a hexagonal socket 158 on its lower end as shown in Figure 5.

The casing 150 also supports two output shafts 158 and 160 which are also retained in place by retaining washers 162.

The shafts 158 and 160 carry secondary gears 170 and 172 both of which are in mesh with the gear 154. The shafts 158 and 160 at their upper ends support hexagonal sockets 174.

The housing 150 also supports a pin 176 which is retained within the casing 150 by retaining washers 178.

As best shown in Figure 6 the gears 154,170 and 172 are retained on the respective shafts by keys 178 which locate in slots 180. However, the gears could be secured to their respective shafts in any manner such as been made integral with the shafts or by welding or the like.

In order to drive the gear box a tool (not shown and which may be the same as the tool previously described) is engaged with hexagonal head 158 so as to provide drive to the shaft 152. Rotation of the shaft 152 will rotate the gear 154 which will inturn rotate the gears 170 and 172 to rotate the sockets 174.

Figure 7 shows how the gear box is engaged with the valve.

The gear box is moved into position so that the sockets 174 engage with the heads 74 on the shafts 120 and 122. As the gear box is moved into this position, as is clearly shown in Figure 7, the pin 176 engages the bottom of the shaft 130 and pushes the shaft 130 upwardly so that the profile 136 is removed from the hexagonal hole 134 in the retaining cap 30. Thus, the locking pinion 128 is now free to rotate since the profile 136 has left the hole 134. The tool can now be engaged with the head 158 so as to provide drive to the gear box to rotate the sockets 174 in the manner previously described so as to rotate the heads 74 and their respective shafts 120 and 122. This will rotate the spur

gears 52 and 58 so that the grinding operation is performed in the manner previously described. Thus, the gear box enables simultaneous rotation of the shafts 120 and 122 to perform the grinding operation by simply engaging the gear box with the head 74 and applying the tool to the head 158.

Once again, in this embodiment of the invention the gear ratio between the first pinion gear 80 and first spur gear 52 and that between the second pinion gear 92 and second spur gear 58 can be different so that rather than the stem 18 remaining stationary during grinding a slow downward movement of the stem 18 can take place. Alternatively, rather than provide the change in gear ratio between the first and second pinion gears 80 and 92 and the respective spur gears 52 and 58, the change in reduction can be provided in the gear box by changing the gear ratio between the gears 154 and 170 compared to that between the gear 154 and 172. This can be accomplished by simply reducing the number of teeth on the gear 172 for example.

It should also be understood that the stem 18 can be driven upwardly and downwardly in the direction of double headed arrow A in Figure 1 by causing the spur gear 58 to rotate the yoke bush 36 whilst holding the stem 18 against rotation by fixing the first spur gear 52 and the first pinion gear 80. Rotation of the yoke bush will therefore provide the opening and closing movement of the valve stem 18. The grinding operation can be performed by releasing the first spur gear 52 or driving it at a different speed to the spur gear 58 so as to impart rotation to the stem 18 to perform the grinding operation.

Since modifications within the spirit and scope of the invention may readily be effected by persons skilled within the art, it is to be understood that this invention is not limited to the particular embodiment described by way of example hereinabove.