PST partial stroke test system
Overview

The PST part-stroke test system is a safety protection scheme for emergency shut-off valves. Its principle is to allow ESD (normally open shut-off valve) valves to perform periodic partial stroke actions. For example: the ESD valve closes 10-30% of the stroke from the fully open position, and performs periodic actions at a certain time interval to better check the movement of the valve stem and judge whether its function is normal. PST is a reliable detection method that does not affect the normal operation of ESD valves.

Application

The ESD valve will be fixed in a certain state and not change when the SIS system is operating normally. Due to this reason, the phenomenon of "fixation" leads to failure. Therefore, tests must be performed to expose those undetected dangerous failures and prevent the ESD valve from being dangerous. The cut-off function (or open function) cannot be performed correctly when the condition occurs. This system does not contain electronic equipment and works purely pneumatically, which is safe, sensitive and reliable.

Features

◎Compared with full-stroke test, partial stroke test (PST) can reduce PFD (probability of failure) value, increase SIL (high safety integrity level), and increase the reliability of ESD valve;
◎Part-stroke test can extend the time interval of full-stroke test, supplement the full-stroke test, reduce test cost;
◎Provide maintenance basis;
◎Due to the PST test, the bypass valve of the ESD valve can be eliminated, reducing the process cost;
◎Automated partial stroke test can enhance the safety of the test and reduce the probability of human error caused by manual testing.

Control schematic diagram

To The circuit of the single-acting actuator controlled ESD valve with the PST part stroke test function is shown in Figure 1. The solenoid valve receives the electric signal to control the actuator switch. When doing the PST part stroke test, press the PST combination valve button to exhaust the lower cavity of the actuator , The actuator moves to the closed position, when it runs to the preset position (usually the preset position is 10%-30% of the closing stroke), the PST combination valve is switched, the lower cavity of the actuator is aired, and the actuator returns to the open position to complete the PST test .

The circuit of the double-acting actuator controlled ESD valve with the PST part stroke test function is shown in Figure 2. Similarly, the solenoid valve receives the electric signal to control the actuator switch. When doing the PST part stroke test, press the PST combination valve button and the pneumatic control valve Pilot exhaust, air control valve switch, the actuator runs to the closed position, when running to the preset position (usually the preset position is 10%-30% closing stroke), the PST combination valve switches, the air control valve pilot receives the air signal , The valve position is switched, and the actuator returns to the open position.

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