Steam turbine protection valves are part of the overall rotating equipment protection system and include trip, trip throttle and non-return valves. Steam turbine protection valves prevent damage to rotating equipment that could be caused by an emergency operating condition, or in the worst case, catastrophic destruction because of overspeed.
A control valve is part of the turbine governor system that regulates the operating speed of the turbine by controlling the amount of steam admitted into the unit. Control valves can be designed with hydraulic or pneumatic actuators that respond to an electric output signal developed by the turbine governor in response to the load requirement of the driven equipment.
Single or multiple control valves are available, depending on the power output of the turbine.