1-inch Pressure Reducing Valve Class #1500 Repair – Son Dong Power Plant

Information:
Mark1 valve, Class #1500, 1 inch, used as a pressure reducing valve in the boiler system of the power plant, equipped with an electric actuator with a 4-20mA control signal.

Condition:
Multiple valves were supplied, but one valve experienced hunting.

MOG’s Solutions:

• Inspected on-site and confirmed the hunting phenomenon. Tried adjusting deadband and hysteresis settings in the electric actuator menu and checked for signal cable interference — no improvement in hunting;

• Ordered a new main board; the manufacturer replaced the main board and feedback encoder, but after some time, hunting still occurred;

• Ordered a new actuator; SVAL replaced the actuator on-site — the valve operated normally afterward.

Assessment:
The hunting issue may originate from the servo motor. Although theoretically, most hunting problems are caused by the main board or encoder, in this case, it was not.