Changeover Valve for Testing Device

Changeover Valve for Testing Device

Function

• The function of the changeover valve is to shut off the flow of trip fluid into the trip fluid circuit while the protective devices are being tested for proper operation by means of the Automatic Turbine Tester (ATT) and to allow control fluid ‘a’ to flow in so that the stop valves do not close when the safety devices respond.

Mode of Operation

• During normal operation, the control fluid ‘a1’ in the space under the lower piston (8) of the changeover valve keeps the valve in the upper end position shown here.
•  In this way, connection ‘x’ is connected with connection ‘x1’ and trip fluid can flow into the trip fluid circuit. 
• The space above the piston (6) (connection ‘a’) remains depressurized during normal operation.
• When safety devices are checked for proper operation, the space below the lower piston (8) is depressurized by means of a solenoid valve and control fluid ‘a’ enters the space above the upper piston, which moves the valve into the lower position. 
• Due to the connection now made between connections ‘a’ and ‘x1’, control fluid ‘a’ can flow freely into the trip fluid circuit, which keeps the stop valves open for the duration of the test. Two limit switches (1) transmit the position of the valve to the control room.