SINGLE SCREW VALVES
Before closing a valve with dust or other contamination on the control screw, it is essential to clean and lubricate the thread.  It is very likely that operating with a dirty thread will cause over-heating, and possibly seizure, of the bronze nut.  It will certainly shorten the working life of these components.  It may be necessary to close the valve in stages, bringing all of the thread within reach.  Clean and re-lubricate with Shell Alvania EP3, or equivalent grease.
Be alert for the possibility of obstructions, either in the valve or in the guide roller tracks, reversing the control mechanism several times, if necessary, in an effort to free-up the movement.

TWIN SCREW VALVES
The notes above apply equally to this model.  The following additional details also require attention:
Before using a twin screw valve after several months of disuse, it is necessary to open the two access hatches, at the top of the valve body, and remove an amalgam of algal by-products and water-borne contaminants, which will be adhering to the two screw threads.
Doing this will require opening the valve in stages, to access all parts of the thread.  Clean the screws, and lubricate with Shell Alvania EP3, or equivalent grease.

ANNUAL MAINTENANCE

SINGLE SCREW VALVES
1.      Apply one squirt of grease, to one nipple, on the right-angle gear box.
No other planned maintenance should be necessary.

TWIN SCREW VALVES
1.      Remove the top dust cover and grease the bearings at four nipple locations.
2.      Grease the exposed gear teeth, with Shell Alvania EP3, or equivalent.
3.      Check oil level in the central gearbox, topping up with any common gear-box oil.  This can also be done at other times, through an access hole in the top of the dust cover.

SEAL REPLACEMENT

SEAL KIT
Seals are supplied fully made up, needing only the punching of holes for the clamp screws, locations of which are traced through the clamp plates from a dismantled valve.  The following kit is supplied:
1.      Two seals, fully assembled.
2.      ‘Bitumastic’ compound for all bolt and screw threads.
3.      ‘Locktite’ 480 Instant Adhesive, for on-site repair of accidental seal damage.
4.      One 15mm wad punch.

CAUTION.  Before dismantling a valve, please note the following:
When re-assembling, and fitting the top drive head assembly to the two main control screws, it is possible to get the threads out of step with each other.  One side of the head assembly will then be higher than the other, by either one rotation, or half a rotation, of a thread.  The head must not be bolted to the valve in this condition.
There are two ways this problem can arise:
Þ    One screw may engage its thread before the other.
Þ    One of the screws may have been replaced on the door rotated 180° from its original  position, as marked in step five, below, of the dismantling procedure.

If this problem has occurred, it is not necessary to dismantle the valve, adjustment can be made from within the drive train as follows:
1.      Remove the dust cover.
2.      On one of the small mitre pinions, loosen the grub screw and remove the key.
3.      Rotate the main input drive shaft by hand, one way or the other, until the head assembly becomes parallel with the top flange of the body, and also, the keyways are again aligned in the pinion.  Refit the key and grub screw.

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.