What is the Set Pressure of a Valve?

1.Concept of Set Pressure

Set pressure, also known as opening pressure, is an important parameter for the operation of a safety valve. The setting of the set pressure directly affects the safety of the equipment’s operation.

2.Determination of Set Pressure

The set pressure of a safety valve is generally not greater than the design pressure of the pressure vessel or pipeline.

In most cases, unless there are special process requirements, the set pressure of a safety valve is 1.10 times the normal working pressure, with a minimum of 1.05 times.

3.Adjustment of Set Pressure

Within the specified working pressure range, the set pressure can be adjusted by rotating the adjustment screw to change the spring pre-compression. To adjust the set pressure, remove the valve cover cap and loosen the locking nut, then adjust the screw.

First, increase the inlet pressure until the valve starts to lift. If the opening pressure is too low, rotate the adjustment screw clockwise to tighten it; if the opening pressure is too high, rotate the screw counterclockwise to loosen it. After adjusting to the required set pressure, tighten the locking nut and replace the cover cap.

If the required set pressure exceeds the spring’s working pressure range, a spring with an appropriate working pressure range should be replaced, and the adjustment should be made accordingly. After changing the spring, the relevant data on the nameplate should be updated.

Important Points to Note When Adjusting Set Pressure

(1) When the medium pressure is close to the set pressure (over 90% of the opening pressure), the adjustment screw should not be rotated, as this may cause the valve disc to rotate, potentially damaging the sealing surface.

(2) To ensure the accuracy of the set pressure, the medium conditions used during adjustment (such as the type of medium and its temperature) should be as close as possible to the actual operating conditions. A change in the medium type, especially when shifting from liquid to gas, can cause a change in set pressure. If the operating temperature increases, the set pressure tends to decrease. Therefore, when adjusting at normal temperature for use in high-temperature conditions, the set pressure at normal temperature should be slightly higher than the required opening pressure.

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