• Pressure adjustment and operating procedures for safety valves

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Pressure adjustment and operating procedures for safety valves

  • Apr 17, 2019
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1. The adjustment of opening pressure

1.1 Before the safety valve is delivered from the factory, the opening pressure should be adjusted one by one to the user's required setting value. If the user proposes a spring working pressure level, it should generally be adjusted according to the lower limit of the pressure level.

1.2 The user must re-adjust the safety valve at the installation site before installing the safety valve on the protected equipment or before installation to ensure that the set pressure value of the safety valve meets the requirements.

1.3 In the range of the spring working pressure level indicated on the nameplate, the opening pressure can be adjusted by rotating the adjusting screw to change the spring compression amount.

1.4 Before rotating the adjusting screw, the valve inlet pressure should be reduced to less than 90% of the opening pressure to prevent the valve flap from being rotated when the adjusting screw is rotated, so that the sealing surface damage is avoided.

1.5 In order to ensure that the opening pressure value is accurate, the medium conditions during adjustment, such as the type of medium and temperature, should be as close as possible to the actual operating conditions. The type of medium changes, especially when the medium is in a different accumulation state (for example, from a liquid phase to a gas phase), and the opening pressure often changes. When the operating temperature rises, the opening pressure generally decreases. Therefore, when it is adjusted at normal temperature and used for high temperature, the set pressure value at normal temperature should be slightly higher than the required opening pressure value. The degree to which it is high is related to the valve structure and material selection, and should be based on the manufacturer's instructions.

1.6 Conventional safety valve is used to fix the additional back pressure. When the opening pressure is adjusted after inspection (the back pressure is atmospheric pressure), the set value should be the required opening pressure value minus the additional back pressure value.

2. Adjustment of discharge pressure and return pressure

2.1 The action test of the valve to the full opening height must be performed when adjusting the valve discharge pressure and the return pressure. Therefore, it is only possible to perform on a large-capacity test device or after the safety valve is mounted on the protected device. The adjustment method varies depending on the valve structure.

2.2 For the structure with the recoil disc and the seat adjusting ring, the valve seat adjusting ring is used for adjustment. Unscrew the adjusting ring and fix the screw, and a tool such as a thin iron rod is inserted from the exposed screw hole, and the teeth on the adjusting ring can be pushed to rotate the adjusting ring to the left and right. When the adjustment ring is rotated counterclockwise to the left, its position is raised, and the discharge pressure and the return pressure are reduced. Conversely, when the adjustment ring is rotated clockwise to the right, its position is lowered, and the discharge pressure and the return pressure are increased. For each adjustment, the amplitude of the rotation of the circle should not be too large (usually rotating several teeth). After each adjustment, the fixing screws should be screwed to ensure the end portion is located in the groove between the two teeth of the adjusting ring, which can prevent the adjusting ring from rotating and does not generate radial pressure on the adjusting ring. For safety reasons, the safety valve inlet pressure should be appropriately reduced (generally less than 90% of the opening pressure) before the adjustment ring is turned to prevent the valve from suddenly opening during the adjustment, resulting in an accident.

2.3 For a structure with upper and lower adjustment rings (one adjustment ring on each of the guide sleeve and the valve seat), the adjustment is more complicated. The seat adjustment ring is used to change the size of the passage between the valve flap and the adjustment ring, thereby changing the amount of pressure accumulated in the chamber between the valve flap and the adjustment ring when the valve is initially opened. When the valve seat adjustment ring is raised, the degree of pressure buildup is increased, so that the phase of the valve proportional opening is reduced and the sudden rapid opening is achieved relatively quickly. Therefore, raising the seat adjustment ring can reduce the discharge pressure. It should be noted that the seat adjustment ring must not rise too close to the valve flap. In this way, the leakage at the sealing surface may cause the valve to suddenly open prematurely, but since the medium pressure is not enough to keep the valve flap in the open position, the valve flap is closed again, and the valve chatters.

The upper adjustment ring is used to change the angle at which the flowing medium is refracted after reflected on the underside of the valve flap, thereby the acting force of the fluid changes, in order to adjust the return pressure.

When the upper adjustment ring is raised, the folding angle is reduced, and the fluid force is reduced accordingly, thereby increasing the return pressure. Conversely, when the upper adjustment ring is lowered, the return pressure is lowered. Of course, while the upper adjustment ring changes the return pressure, it also affects the discharge pressure, that is, raising the upper adjustment ring causes the discharge pressure to increase, and lowering the upper adjustment ring to lower the discharge pressure, but the degree of influence is not as obvious as the return pressure.

3. Seal
After the safety valve has been adjusted, it should be sealed to prevent any changes to the adjusted condition. When repairing and maintaining the safety valve, the position of the adjusting screw and the adjusting ring should be recorded before disassembling the valve to facilitate the adjustment after repairing. Seal it again after re-adjustment.