NORMAL USE.  Open the valve by rotating the handwheel in a clockwise direction, as viewed from above.  It will be felt when the valve is fully open, any further forced turning will damage the mechanism.  While closing in the opposite direction, take the same care not to over-stress the mechanism.

Should the handwheel become hard to turn or the mechanism feel rough, servicing will be necessary.  Do not force the handwheel with additional leverage, as the screw system is capable of causing structural damage.

OBSTRUCTIONS.  Resistance of a foreign body in the valve will be felt on the handwheel.  Attempt to clear a blockage by opening and closing several times, as far as possible.  When a valve is brought to the nearly closed position, the resulting high velocity flow is often sufficient to dislodge an obstruction.

If these efforts fail and it becomes necessary to devise a more involved procedure,  pay particular attention to the hazards of working around water intakes

LUBRICATION.  Valves in constant use should have the control thread greased with Shell Alvania EP3, or equivalent, annually.  Thrust bearings are packed with general purpose grease at assembly and need no attention between major overhauls.  Bolts should be replaced with an application of an anti-seize copper compound.  There are no grease nipples on the valve.

DISMANTLING.  Remove the plates covering the two access holes, located midway down the side frames.  Raise the valve door, until the lower bronze rollers can be removed through the access holes.  The rollers will slide out easily, there are no retainers to undo.

Remove four bolts securing the top cross frame.  With suitable lifting tackle, raise the sub-assembly comprising; control column, top cross frame, door.  When the upper door rollers appear above the side frames, they should be removed.  The sub-assembly can now be lifted clear.

SEAL REPLACEMENT.  The extruded rubber seal has serrated edges, to tightly grip within the door recess.  Careful examination will reveal that one side of the rubber is slightly convex, while the other is slightly hollow.  This feature could easily be missed, if not pointed out.  The rubber is inserted, so that the slightly raised side is outermost, to be the sealing surface in contact with the stainless seat.

Remove and save the rivets, remove the old rubber.  Carefully clean the recess with a wire brush, small angle grinder, or by hand with clean coarse emery tape.

Check that the rubber has one end square and neat.  Roughen the back of the rubber by hand, using clean coarse sandpaper.  Apply 'Locktite' 480 Instant Adhesive, or an approved equivalent, to the back of the rubber.

Begin seal replacement by inserting the good end of rubber into the groove, in the same position as occupied by the original ends of the old rubber (between the two close rivet holes).  Hammer the rubber into the recess, working progressively around the ring. When about 200mm from the end, cut the rubber, to be about 3mm 'too long'.  Place this end into position, and hammer the remaining arch into the groove.