Batescrew Extreme Head Valves
Operation Annual Maintenance Seal Replacement
NOTE: Power operated
systems should be torque-limited to 860 Nm, equal to
the effort of one man operating a 500mm handwheel.
SINGLE SCREW VALVES
TWIN SCREW VALVES
SINGLE SCREW VALVES
TWIN SCREW VALVES
Before dismantling a valve, please note the following:
If this problem has occurred, it is not necessary
to dismantle the valve, adjustment can be made from within the drive
train as follows:
SEAL REPLACEMENT PROCEDURE.
1. Remove all bolts around the top flange. Gently take the weight of the head assembly with the 5 tonne chain block. Run the control mechanism in reverse (as for closing the valve), whilst taking up the weight with the hoist. When the Head is clear of the two control screws, it can be lowered over the side onto the special support bracket.
2. With the probe rod attached, lower the grappling tool into the valve. Locate the central lifting lug on top of the door and insert the gooseneck, using the probe rod. This takes a certain amount of ‘fishing’. Check that the two load bearing pins have been inserted in the telescopic side posts of the gantry. The two half tonne chain blocks are for erection of the gantry only and will not carry the working load.
3. Raise the door with the 5 tonne block, keeping manual control of the two screws. One man will be needed on each screw and a third on the chain block. Two loops have been provided on the top rail of the gantry to hold the screws, once they have reached this level. The probe rod can be allowed to hang loose.
4. When the top of the door is exposed, check the grappling tool, hammering it fully home if necessary, engage the safety latch and remove the probe rod.
5. Mark each control screw in two ways: RH/LH and Front/Back. It will be essential to replace the screws, each on its correct side of the valve, also with each screw facing its original direction (not rotated half a turn). Each screw must have these two markings applied, before removal. See the note above in ‘CAUTION’. After marking, remove both screws and the detach the probe rod.
6. Anything dropped into the valve chamber, if larger than a seal retaining screw, will have to be recovered before re-assembly. We therefore recommend that the door be fully removed at this stage and a heavy tarpaulin draped into the valve and secured externally. Leave enough slack to allow the door to be lowered somewhat, bringing the top of the seal within reach.
7. Mark the seal clamp plates, for later replacement in the same positions, and remove. On some valves there will be loose backing plates under the seals, these must also be marked.
8. Using the clamp plates as templates, trace screw positions onto the seals and punch the holes. Keep seals and plates together in matched sets.
9. Fit the new seals to the door, applying ‘Bitumastic’ to all threads.
10. After removing the tarpaulin, the valve can be re-assembled. It would be well worth the effort to tie all spanners etc. with light cord, before removing the tarpaulin.
11. Replace the two control screws, on the correct sides (they are left and right hand threads), and with each screw facing the correct way, marked in step5. Re-fit the probe rod to the grappling tool and disengage the safety latch.
12. Lower the door and screws, then remove the lifting tackle.
13. Hoist the drive head assembly into position and rotate the input shaft by hand, to engage the threads. Both screws must engage on the same revolution.
14. Run the threads down, keeping the weight with the chain block, until the Head is close to the top flange. Check that it is parallel with the flange, if not, see the notes in ‘CAUTION’ above, for a simple method of correction .
15. Finishing the job from this stage and dismantling the gantry, is straight forward.