Val-Matic Tilted Disc Check Valve - Manual (Page 11)

10
OPTIONAL TOP DASHPOT
DESCRIPTION: The Top Mounted Oil Dashpot
(TMOD), when required, is installed in the top
inspection port of the Tilted Disc Check Valve and is
attached with linkage to the disc. This unit provides
single-stage speed control of valve opening and two-
stage speed control of valve closing to reduce
pressure surges on pump start-up and shut-down.
The dashpot unit consists of a high-pressure oil
hydraulic cylinder, two adjustable flow control valves,
a pressurized oil reservoir, a non-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
spacer also contains the connecting rod bushing,
bushing retainer plate and screws, o-ring seals,
external and internal rod wipers, and the connecting
rod which is connected to the piston rod of the
hydraulic cylinder with a special quick coupling
assembly. The connecting rod is attached to the
check valve disc via links and pins.
OPERATION: Upon start-up, the forward flow of the
water will open the check valve. The hydraulic fluid
within the top portion of the dashpot cylinder is
slowly bled through the top external flow control
valve, until the valve travels to the full open position.
On pump shutdown, the reversal of flow will start to
drive the disc to the closed position. For the first
90% of the disc travel, the hydraulic fluid within the
bottom portion of the dashpot cylinder is slowly bled
through the bottom flow control valve. The cylinder’s
internal cushion plunger then enters the cushion
cavity located in the head of the hydraulic cylinder,
provides a finer speed control (second stage) over
the final 10% of disc travel to the closed position.
INSTALLATION: Follow the installation instructions
for the basic valve for installation of the valve in the
line. Use the following steps to start up the TMOD.
1. The external flow control valves should be set in
the full open position (counterclockwise).
2. The cylinder’s internal cushion adjustment screw
in the face of the head is factory set at 4 turns
from being bottomed out, see Figure 6.
3. The dashpot has been filled with oil in the factory
and no additional fluid is required unless external
leakage is observed. (See maintenance section
on how to check fluid level).
4. Using a bicycle pump, charge the pressurized
reservoir until the air pressure equals 20% of the
water pressure on the discharge or downstream
side of the check valve.
Figure 5. Top Mounted Oil Dashpot (TMOD)
5. Start the pump and observe the action of the
valve through the opening cycle and allow the
water system pressure to stabilize.
6. Shut down the pump and observe by sound and
by observing the indicator the closing action of
the valve.
7. If pressure surging is observed on the valve
opening or if water hammer noises exist on valve
closure, the appropriate external flow control
valve can be gradually turned to a smaller
number setting until optimum valve operation is
achieved, see Figure 9. The unit is designed to
control the operating time between 5 and 30
seconds.
Figure 6. Internal Cushion Adjustment