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Safety Valve / Pressure Relief Valve

Pressure safety valve is sometimes known as Pressure Relief Valve. Its purpose is to prevent a pressure in a pressurized vessel or line to go above the set point by venting to atmosphere or diverting the flow to an alternate channel.

It can be used for all mediums including air, liquids, gases, water and oil.

As it is considered a critical component, some authorities (eg. SINGLAS) may require periodic testing to certify that it is in working order. One of the common tests involve a ‘pop test’.

Important engineering considerations involve sizing and material selection.

Model

Application

Max Min Temperature (°C)

Material

Connection

Size

Pressure

Medium

Max Capacity kg/h

Body and Cover Material

Secondary Pressure Range

Type of Trap

Glass O.D / Length

Pipe Size

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Safety Valve / Pressure Relief Valve

    Description

    What is a Pressure Safety Valve

    These valeves protect pressure vessels from overpressure by opening automatically when the set pressure is reached.

    Parts of a Safety Valve

    1. Nozzle – Connection of the safety valve

    9. Adjusting Screw – This is where you adjust the set pressure

    4. Cap – Prevents access to the adjustment screw

    11. Spring – Holds the disc down to close the safety valve

    5. Disc – Blocks the orifice to close the safety valve

    Sizing of Safety Valves: Basics

    Proper sizing involves complex calculations to determine the required orifice size. It depends various factors such as the type of fluid, temperature, maximum set pressure and the required relief capacity of the safety valve. This ensures that during an emergency, the relief valve is able to vent enough fluid to reduce the pressure.

    Determining the Set Pressure

    The set pressure usually depends on the maximum working pressure of the equipment or line the safety valve is supposed to protect. Ideally, it should be set around 10% below this point.

    The calculation of the orifice size is usually done using software. Some manufacturers also provide a capacity chart to determine the required orifice size.



    Contact us for help in selection and sizing of here

    Calculating the orifice size

    Maintenance & Calibration Procedure

    It is important and sometimes mandatory by law to perform calibration and testing of the relief valve. The purpose is to ensure that the valve is in proper working condition and will not fail when it needs to discharge pressure.

    In Singapore, it is mandatory for all safety valves installed at boilers and pressure vessels to undergo re-certification regularly. This is regulated by SINGLAS.

    A pressure relief valve may fail due to:

    • Repeated opening and closing
    • Dust, rust and other debris from the pipe
    • The valve has remained closed for long periods of time
    • Normal wear and tear

    Calibration Procedure

    Performing calibration and servicing requires a proper test bench that can deliver air or water at different pressure to perform the required tests. During a pop test, the pressure is slowly increased until the valve opens slightly. This has to be done carefully to prevent damage to the valve. A leakage test must also be carried out to ensure that the valve is not leaking.

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