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Basic knowledge of safety valve

Jul 30, 2018

Basic knowledge of safety valve

1) valves: general name of mechanical products with movable mechanism installed on pressure vessels, pressurized equipment and connecting pipes to control the flow of media.

2) nominal diameter of the valve: refers to the nominal diameter of the pipe between the valve and the pipe and all other accessories. The unit is mm (represented by DN).

3) safety valve: it is an automatic valve that can discharge a rated amount of fluid only by the force of the medium without any external force to prevent the pressure in the system from exceeding the predetermined safety value.When pressure returns to normal, a valve that closes itself and prevents the medium from continuing to flow out.4) working pressure P: pressure of the valve at the service medium temperature.

5) operating temperature T: the temperature of the valve in the service medium.

6) setting pressure Ps: the predetermined pressure that the safety valve starts to open under operating conditions.Under this pressure, the force to open the disc is balanced with the force to keep the disc in the seat.

7) back seat pressure Pr: refers to the static pressure at the inlet of the valve when the valve reaches the discharge state, the medium pressure drops to a certain value, and the disc recontacts with the seat, i.e. when the opening height becomes zero.8) opening and closing pressure difference: the difference between the setting pressure of the safety valve and the pressure of the return seat is usually expressed as the percentage of the setting pressure. Only when the setting pressure is very low is Mpa used.

9) discharge pressure Pb: setting pressure plus excess pressure (excess pressure refers to the pressure that exceeds the setting pressure of the safety valve, usually expressed as a percentage of the setting pressure)

10) opening height h: the actual lift of the disc away from the closed position.

11) channel area A: refers to the minimum cross-sectional area of the flow passage between the inlet end of the valve and the sealing cover of the closing piece, used to calculate the theoretical displacement without any resistance influence.The diameter of flow passage corresponding to flow passage area A is do (throat diameter).

12) displacement coefficient Kd: the ratio of actual valve displacement to theoretical displacement.

13) sealing test pressure Pt: the pressure specified in the sealing test shall be measured under such pressure to measure the leakage rate through the sealing surface of the closed parts.Generally, 90% of the setting pressure is taken as the sealing test pressure.

14) factory test;Test the strength, sealing and opening pressure of the shell before leaving the factory.


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