(1) Adjustment of opening pressure
① Before leaving the factory, the opening pressure of safety valves should be adjusted one by one to the set value required by the user. If the user proposes the working pressure level of the spring, it should generally be adjusted according to the lower limit value of the pressure level before leaving the factory.
② Before installing the safety valve on the protected equipment or before installation, the user must readjust it at the installation site to ensure that the set pressure value of the safety valve meets the requirements.
③ Within the working pressure range of the spring 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 inlet pressure of the valve should be reduced to less than 90% of the opening pressure to prevent the valve disc from being driven to rotate and damaging the sealing surface.
⑤ To ensure accurate opening pressure values, the medium conditions during adjustment, such as medium type and temperature, should be as close as possible to the actual operating conditions. Changes in the type of medium, especially when the accumulation state of the medium is different
(For example, when transitioning from a liquid phase to a gas phase), the opening pressure often changes. When the working temperature increases, the opening pressure generally decreases. Therefore, when adjusting at room temperature for high temperatures, the set pressure value at room temperature should be slightly higher than the required opening pressure value. The degree of height is related to the valve structure and material selection, and should be based on the manufacturer's instructions.
⑥ Conventional safety valves are used to fix the additional back pressure. When the opening pressure is adjusted after inspection (the back pressure is atmospheric pressure at this time), the setting value should be the required opening pressure minus the additional back pressure.
(2) Adjustment of discharge pressure and reseating pressure
① To adjust the discharge pressure and reseating pressure of the valve, an action test must be conducted to reach the full opening height of the valve. Therefore, it is only possible to perform the test on a large capacity test device or after the safety valve is installed on the protected equipment. The adjustment method varies depending on the valve structure.
② For structures with recoil discs and valve seat adjustment rings, the valve seat adjustment ring is used for adjustment. Unscrew the fixing screw of the adjustment ring, insert a thin iron rod or other tool from the exposed screw hole, and then move the gear teeth on the adjustment ring to rotate left and right. When the adjusting ring is rotated counterclockwise to the left, its position increases, and the discharge pressure and reseating pressure both decrease. On the contrary, when the adjusting ring is rotated clockwise to the right, its position decreases, and the discharge pressure and reseating pressure both increase. During each adjustment, the adjustment should not be too large (usually by turning a few teeth). After each adjustment, the fixing screw should be tightened so that its end is located in the groove between the two teeth of the adjustment ring, which can prevent the adjustment ring from rotating and not generate radial pressure on the adjustment ring. For safety reasons, before moving the adjustment ring, the inlet pressure of the safety valve should be appropriately reduced (generally lower than 90% of the opening pressure) to prevent the valve from suddenly opening during adjustment and causing accidents.
③ For structures with upper and lower adjustment rings (with one adjustment ring on each guide sleeve and valve seat), the adjustment is more complex. The valve seat adjustment ring is used to change the size of the channel between the valve disc and the adjustment ring, thereby changing the degree of pressure accumulation in the chamber between the valve disc and the adjustment ring during the initial opening of the valve. When the valve seat adjustment ring is raised, the degree of pressure accumulation increases, thereby reducing the proportional opening stage of the valve and quickly reaching a sudden rapid opening. Therefore, raising the valve seat adjustment ring can reduce the discharge pressure to some extent. It should be noted that the valve seat adjustment ring should not be raised too close to the valve disc. In that way, leakage at the sealing surface may cause the valve to suddenly open prematurely, but due to insufficient medium pressure at this time to keep the valve disc in the open position, the valve disc will then close again, causing frequent valve jumps.
Seat adjustment: The ring is mainly used to reduce the valve proportion, adjust the opening stage and discharge pressure, while also affecting the reseating pressure.
The upward regulating ring is used to change the angle at which the flowing medium bends after being reflected on the lower side of the valve disc, thereby changing the magnitude of the fluid force and adjusting the reseating pressure. When the upper ring is raised, the turning angle decreases, and the fluid force decreases accordingly, resulting in an increase in the reseating pressure. On the contrary, when the upper adjustment ring is lowered, the reseating pressure decreases. Of course, raising the adjusting ring not only changes the reseating pressure, but also affects the discharge pressure. Raising the upper adjusting ring increases the discharge pressure, while lowering the upper adjusting ring reduces the discharge pressure. However, the degree of its impact is not as significant as the reseating pressure.
(3) Lead sealing
After adjusting the safety valve, it should be sealed with lead to prevent arbitrary changes to the adjusted condition. When repairing the safety valve, the position of the adjusting screw and adjusting ring should be noted before disassembling the valve, in order to facilitate the adjustment work after the repair. After readjustment, lead sealing should be applied again.