In many process plants, a shutoff valve in a safety loop is usually equipped with a solenoid valve for emergency shutdown and with limit switches for position feedback. The mere shutoff valves remain unused in one position during normal operation over a period of many months or years even. A special test procedure was developed, which allows partial stroking of the valves without causing any drastic interruptions in the production process. The valve is only partially stroked to test it, which does not perceptibly impair plant operation. This allows the plant operator to verify whether the valve will shut down in the event of emergency.
Samson’s (Germany) Type 37303 Electropneumatic Positioner, which has also been enhanced to include an ESD function, has been designed to perform partial stroke tests on the valve. The combination of certified components and positioner functions meets all the necessary safety requirements. The positioner can be mounted on the valve in addition to the solenoid valve or to replace it. It allows the valve to be moved precisely to follow the set point within the valve’s working range. The partial stroke test completely integrated into the positioner detects a sticking valve caused, for example, by corrosion. Test schedules are made flexible and can be prolonged, if necessary. The required test validation can be performed simply by using the corresponding instrumentation and initiating it over a commonly available SIS logic solver.
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