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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.
A pressure wave, which represents a rapid pressure and associated flow change, travels at sonic velocity for the liquid pipe medium, and the wave is partially transmitted and reflected at all discontinuities in the pipe system (pipe junctions, pumps, open or closed ends, surge tanks, etc.)
Valves and their types and identifications (e.g. isolation, shutoff, relief and safety valves, valve interlocks) Control inputs and outputs (sensors and final elements, interlocks) Miscellaneous - vents, drains, flanges, special fittings, sampling lines, reducers and swages; Interfaces for class changes; Computer control system
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.
A control valve is a valve used to control fluid flow by varying the size of the flow passage as directed by a signal from a controller. [1] This enables the direct control of flow rate and the consequential control of process quantities such as pressure, temperature, and liquid level.
When the pilot valve reaches set pressure it opens and releases the pressure from the dome. The piston is then free to open and the main valve exhausts the system fluid. The control pilot opens either to the main valve exhaust pipe or to atmosphere. Snap acting At set pressure the valve snaps to full lift.
This means that they are installed as a component of the completion string and run in during completion. Retrieving the valve, should it malfunction, requires a workover. The full name for this most common type of downhole safety valve is a Tubing Retrievable Surface Controlled Sub-Surface Valve, shortened in completion diagrams to TRSCSSV.
A blowdown valve (BDV) is a type of shutdown valve designed to depressurize a pressure vessel by directing vapour to a flare, vent or blowdown stack in an emergency. BDVs fail-safe to the open position upon failure of the control system. [1] The type of valve, type of actuation and performance measurement are similar to an ESD valve.