![]() ![]() Point 1 : This solenoid valve arrangement would be designated 1oo2 from the perspective of starting the turbine, since only one out of the two solenoids needs to trip in order to initiate the turbine start-up. ![]() ![]() This much is evident from the curved arrows showing air flowing to the “Vent” ports in a de-energized (DE) condition.Īn additional valve (PY-590) guarantees the piston actuator’s upward motion by simultaneously applying air pressure to the bottom (point 2) of the actuator if ever air is vented from the top.Īs an additional feature, the left-hand solenoid valve (SOV-590A) has a manual “Reset” lever on it, symbolized by the letter “R” inside a diamond outline. If either (point1) of the two solenoid valves de-energizes, instrument air pressure will vent from the top of the piston actuator to atmosphere, causing the steam valve to “fail” to the full-open position and send steam to the turbine. Take the following segment of an actual P&ID for a steam turbine-driven pump control system for example, where a pair of 3-way solenoid valves control instrument air pressure to a piston-actuated steam valve to start the turbine in the event that an electric motor-driven pump happens to fail: The choice to use a solenoid’s energized or de-energized state to perform a specific function is left to the system designer, but nevertheless it is important for all maintenance personnel to know in order to perform work on a solenoid-controlled system. Solenoid valves may be used in such a way that they spend most of their time de-energized, energizing only for brief periods of time when some special function is required.Īlternatively, solenoids may be maintained in an energized state, and de-energized to perform their design function. ![]()
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