Val-Matic Tilted Disc Check Valve - Manual (Page 14)

13
OPTIONAL TOP DASHPOT (Cont’d)
Figure 8. Quick Change Coupling
The Quick Change Coupling provides for easy
removal and maintenance of the dashpot assembly
while the check valve is under pressure. The
coupling also provides a self-aligning connection
which prolongs the life of the seals and bushings in
the cylinder and dashpot assembly.
The coupling is formed in two half-sections. The
sections are joined together around the ends of the
cylinder rod and the connecting rod and secured
with an outer slip-type coupling retainer.
TROUBLESHOOTING VALVE WITH TOP
MOUNTED OIL DASHPOT: The top mounted oil
dashpot is linked directly to the disc. Flow control
valves (38) control the opening and closing speeds
in the 5-30 second range. The last 10% of closure is
also controlled by the cylinder cushion control.
1. Valve Does Not Close Fully: Check air pressure
in reservoir; should be at least 20% of the water
system pressure on the downstream side of the
valve or 10 psig minimum. The pressure can be
increased until the valve closes but the opening
stroke may be reduced. Add grease to dashpot
fitting (23). Open lower flow control valve (38)
further to allow greater oil flow. Readjust flow
control valve until slam is diminished. A
differential pressure across of the disc of at least
50 psig is typical for dashpot valves. If the
pressure is lower, the dashpot is probably not
needed and may interfere with valve operation.
2. Valve Slams Closed: Dashpot should prevent
slamming by controlling the valve closure.
Throttle down the bottom flow control valve (38)
to slow down valve closure. If problem persists,
check oil level in unit per the Instruction Manual.
3. Valve Does Not Open: Open top flow control
valve (38) fully counterclockwise. Check pressure
differential across disc; upstream pressure must
be greater than downstream pressure. Verify that
downstream shutoff valve is open and there is no
line blockage. Add grease to valve and dashpot
grease fittings (23). Lower pressure on air tank
(pressure should be 20% of water system
pressure). Pressure can be temporarily reduced
to 0 psig to assist in valve opening. Drain the
pipe on both sides of the valve, remove
inspection cover (13), and inspect disc ring (8)
and seat ring (10) for damage or wedged debris.
If debris is wedged in the valve, it may de
necessary to jack open the disc with a hydraulic
jack. See “Inspection of Valve” on page 1 of this
guide for further information.
4. Noisy Operation or Vibration: Flow noise is
normal. Loud flow noise similar to hammering
may be cavitation from dropping high pressures
across valve during opening and closing. Open
flow control valves (38) to provide shorter
operating times.
5. Pump Backspins: Valve is closing too slowly.
Open bottom flow control valve (38) further. If
surges in the pipeline result, surge relief devices
on the pipeline probably need attention.
6. Pressure Surges: Throttle down bottom flow
control valve (38) further to increase closing time.