Val-Matic Tilted Disc Check Valve - Manual (Page 8)

7
CAUTION
Flow control valves should not be used at
settings below the blue band (second from the
bottom). Lower settings will allow small
particles of silt present in the hydraulic fluid
to clog the valve and cause the BMOD to bind
and result in damage to the valve or dashpot.
OPTIONAL BOTTOM DASHPOT
DESCRIPTION: The Bottom Mounted Oil Dashpot
(BMOD), when required, is installed in the bottom
inspection port of the Tilted Disc Check Valve. This
unit provides control of the disc’s final 10% of travel
to the close position to reduce water hammer
normally associated with rapid flow reversal
conditions that exist on pump shut down. The unit
consists of a high-pressure hydraulic cylinder,
adjustable flow control valve, pressurized oil
reservoir and piping.
A dashpot spacer which provides an air gap,
connects the hydraulic cylinder and the dashpot
cover, to prevent pressurized hydraulic fluid from
entering the valve housing and contaminating the
water system. The dashpot cover contains a
snubber rod bushing and snubber rod which
contacts the disc and the spring retainer assembly
that is attached to the piston rod of the hydraulic
cylinder.
OPERATION: Upon start-up, the forward flow of the
water will open the check valve. The snubber rod is
extended by the piston spring and the pressurized
hydraulic fluid in the cylinder. On pump shutdown,
the reversal of flow will close the check valve. Prior
to the valve fully closing, the disc will make contact
with the snubber rod and the hydraulic fluid will
slowly bleed through the adjustable flow control
valve, thus allowing the disc to move slowly into the
seat. Some reverse flow and pump backspinning
may occur during this process.
INSTALLATION: The BMOD may be installed at the
factory (valves larger than 12”) or it may be installed
in the field as follows.
1. Remove the valve bottom inspection hole cover
(13) and gasket (14).
2. Clean the gasket residue from the face of the
inspection hole port.
3. Place the o-ring (70) into the groove of the
dashpot cover (60).
4. Install the dashpot unit into the inspection hole
port, aligning the snubber rod bushing to the
notch in the inspection hole port.
5. Install the dashpot cover bolts (14) and tighten.
6. Start the unit with the flow control valve (38) in
the full open position (fully counterclockwise).
Figure 3. Bottom Mounted Oil Dashpot
7. The BMOD has been filled with oil at the factory.
Using a bicycle tire pump inject air into the air
fitting (55) until the pressure is 50 psi higher than
the water system pressure on the discharge side
of the check valve. The air pressure acts to
counter-balance the force created by the internal
water pressure acting on the area of the snubber
rod (63). The air pressure and spring (71) work
to extend the snubber rod when the check valve
opens.
8. Start the pump and allow the check valve to fully
open.
9. Shut down the pump and observe the action of
the valve closure. If a slam occurs, the flow
control valve can be gradually turned down
(clockwise), until optimum operation is achieved,
see Figure 9. The BMOD unit is designed to
control the closing time between 1 and 5
seconds.