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Valve explain
Jul 17, 2018

Nominal pressure: indicates the maximum allowable pressure of the safety valve at normal temperature. The safety valve for high temperature equipment should not consider the reduction of the allowable stress of the material at high temperatures. Safety valves are designed and manufactured to nominal pressure standards.


Opening pressure: also called rated pressure or setting pressure, refers to the inlet pressure of the safety valve flap when it starts to rise under operating conditions. Under this pressure, there is a measurable opening height, and the medium is visually or audibly perceptible. Continuous discharge status.


Discharge pressure: The inlet pressure at which the valve flap reaches the specified opening height. The upper limit of discharge pressure is subject to the requirements of relevant national standards or specifications.


Excessive pressure: The difference between the discharge pressure and the opening pressure, usually expressed as a percentage of the opening pressure.


Respiratory pressure: After the discharge, the valve flap is re-contacted with the valve seat, that is, the inlet pressure when the opening height becomes zero.


Opening and closing pressure difference: the difference between the opening pressure and the returning pressure, usually expressed as a percentage of the return pressure and the opening pressure, and is expressed by the pressure difference between the two when the opening pressure is low.


Back pressure: The pressure at the outlet of the safety valve.


Rated discharge pressure: The upper limit of the discharge pressure specified by the standard.


Seal Test Pressure: The inlet pressure at which the seal test is conducted, at which the leak rate through the seal face of the closure is measured.


Opening height: The actual lift of the flap away from the closed position.


Flow path area: refers to the minimum cross-sectional area of the flow path between the inlet end of the valve flap and the sealing surface of the closing member. It is used to calculate the theoretical displacement without any resistance effect.


Runner diameter: corresponds to the diameter used for the runner area.


Curtain area: The area of a cylindrical or conical surface formed between the sealing faces of the valve flap when it is above the valve seat.


Discharge area: The minimum cross-sectional area of the fluid passage when the valve is discharged. For a fully-inspired safety valve, the discharge area is equal to the flow area; for a micro-open safety valve, the discharge area is equal to the curtain area.


Theoretical Displacement: The calculated displacement of the ideal nozzle with the cross-sectional area of the flow passage equal to the area of the safety valve runner.


Displacement coefficient: the ratio of actual displacement to theoretical displacement.


Rated displacement factor: The product of the displacement coefficient and the reduction factor (0.9).


Rated displacement: Refers to the part of the actual displacement that is allowed to be the basis for the safety valve.


Equivalent calculation displacement: refers to the calculated displacement of the safety valve when the conditions of pressure, temperature, medium properties and the like are the same as the applicable conditions of the rated displacement.


Frequency hopping: The safety valve flap quickly and abnormally moves back and forth, and the valve flap contacts the valve seat during motion.


Flutter: The safety valve flap moves back and forth quickly and abnormally, and the valve flap does not touch the valve seat during motion.