Maintenance Procedures. Distribution system valves are usually left open
and operated only during emergencies. To make sure that distribution valves operate
when needed, each valve in the system should be operated twice a year and any
indicated maintenance carried out. To check the operation of the valve, first close the
valve completely and then open it completely. Back off on the valve about one turn to
avoid locking the valve in an open position. If the valve does not operate properly,
perform necessary maintenance and repair at once.
Valve Seating. The usual cause for a valve not seating properly in
the closed position is foreign matter lodged on the valve seat. Open the valve slightly
to give a high-velocity flow across the valve seat. If necessary, open a hydrant to
increase flow enough to flush foreign matter from the valve seat.
Packing. Check and lubricate the valve-stem packing. Dry
packing will impede valve closure at all points of the stem movement. Lubricate dry
packing by pouring a mixture of half kerosene and half lubricating oil down a 1/2-inch
(13-mm) pipe to discharge the mixture onto the stem below the operating nut. If the
packing leaks, dig up the valve, tighten the packing gland, or replace the packing as
necessary. To reduce leakage while replacing packing, open the valve as wide as
O-Ring Seals. Most modern valves use O-ring seals rather
than packing. If water is leaking around the stem, replace the O-rings.
Valve Stem. Valve stems may be out of alignment or broken, or
may have stripped threads. If the valve stem is out of alignment, the valve operates
easily near open or closed positions, but not when the valve is partially closed.
A broken or stripped stem permits unlimited turning of the stem without closing the
valve. All of the above conditions require replacing the valve stem. Follow the
manufacturer's instructions for removing and inserting the stem. If the valve-stem nut is
missing or damaged, replace it.
Valve Seat Refacing. When a gate-valve seat leaks, remove the
valve and reface the valve seat. The procedure to follow should be detailed in the
manufacturer's instructions and includes these general terms:
Remove the bonnet. Inspect and clean all working parts.