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Partial stroke testing (or PST) is a technique used in a control system to allow the user to test a percentage of the possible failure modes of a shut down valve without the need to physically close the valve. PST is used to assist in determining that the safety function will operate on demand.
Proof test - A manual test that allows the operator to determine whether the valve is in the "as good as new" condition by testing for all possible failure modes and requires a plant shutdown Diagnostic Test - An automated on-line test that will detect a percentage of the possible failure modes of the shutdown valve.
One example of SIS is a temperature sensor that provides a signal to a controller, which compares the sensed process temperature to the desired temperature setpoint and sends a signal to an emergency on-off valve actuator which stops the flow of heating fluid to the process if the process temperature is exceeded by an unsafe margin.
Shut-off / On-off valve: These valves are either completely open or closed. Examples: Gate valve, ball valve, globe valve, angle valve, pinch valve, diaphragm valve; Check valve: Allows flow only in a single direction; Steam conditioning valve: Regulates the pressure and temperature of inlet media to required parameters at outlet.
A relief valve DN25 on cooling water pipe from heat exchanger Schematic diagram of a conventional spring-loaded pressure relief valve. A relief valve or pressure relief valve (PRV) is a type of safety valve used to control or limit the pressure in a system; excessive pressure might otherwise build up and create a process upset, instrument or equipment failure, explosion, or fire.
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Increased pressure or decreased pressure closes the valve (without using any external power sources). Installing a bypass pipe with a pushbutton to open valve (normally spring closed valve) between the inlet and outlet of the security valve can let the upstream and downstream pressure can be equalized on both sides of the security valve, so it ...
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