The safety valve needs to go through the following operations when opening the pressure in the early stage:
(1) Opening pressure adjustment
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.
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.
3 Within 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.
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 is damaged.
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.
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 setting value should be the required opening pressure value minus the additional back pressure value.
(2) Adjustment of discharge pressure and return pressure
1 Adjusting the valve discharge pressure and the return pressure must perform the action test of the valve to the full opening height. Therefore, it is only possible after the large-capacity test device or after the safety valve is installed on the protected device. The adjustment method varies depending on the valve structure.
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 fixing screw and extend a tool such as a thin iron rod from the exposed screw hole to push the gear teeth on the adjusting ring to make the adjusting ring rotate 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, adjust: the amplitude of the rotation of the circle should not be too large (generally rotate a few teeth). After each adjustment, the fixing screws should be screwed so that the end 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.
3 For the structure with the upper and lower adjustment rings (the guide sleeve and the valve seat have one adjustment ring), 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 jumps.
Seat adjustment: The ring is mainly used to reduce the valve ratio, the opening stage and adjust the discharge pressure, and also affect the return pressure.
The upper adjustment ring is used to change the angle of the fluid medium after the lower side of the valve flap is reflected, thereby changing the force of the fluid, thereby adjusting the return pressure. When the upper adjustment ring is raised, the folding angle is reduced and the fluid force is reduced, 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 pressure of the seat back, 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 reduce the discharge pressure, but the degree of influence is not as good as The seat pressure is as obvious.
(3) Seal
After the safety valve has been adjusted, it should be sealed to prevent any changes to the adjusted condition. When refurbishing the safety valve, note the position of the adjustment screw and adjustment ring before disassembling the valve to facilitate adjustment after trimming. Sealed again after re-adjustment.