How to Adjust and Verify Safety Valves

1. There are two methods for safety valve verification: on-site verification (online verification) and verification bench verification: 1. On-site verification should be performed as far as possible when conditions permit, because on-site verification is more suitable for actual operating conditions, and therefore more reliable. The advantages of on-site calibration: it is convenient to calibrate the welded safety valve, and the back-seating pressure can be measured, and the measurement is accurate. The disadvantage is that the calibration time is long, and the system has to be repeatedly boosted, which is uneconomical and dangerous, and cannot be tested for sealing. 2. Calibration bench calibration: Before leaving the factory, a safety valve calibration bench at room temperature is generally used to set the opening pressure of the air medium and test the tightness. The safety valve normal temperature calibration bench can only do opening pressure setting and sealing test. Two: Adjustment of safety valve 1. Adjustment of opening pressure of safety valve ① Before leaving the factory, the opening pressure of safety valve should be adjusted one by one to the setting 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 of the pressure level before leaving the factory. ② Before installing the safety valve on the protected equipment or before installation, the user must re-adjust at the installation site 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 changing the spring compression amount by rotating the adjusting screw. ④Before rotating the adjusting screw, the inlet pressure of the valve should be reduced to below 90% of the opening pressure to prevent the valve disc from being driven to rotate when the adjusting screw is rotated, resulting in damage to the sealing surface. ⑤ In order to ensure the accuracy of the opening pressure value, the medium conditions during adjustment, such as medium type, temperature, etc., should be as close to the actual operating conditions as possible. When the type of medium changes, especially when the accumulation state of the medium is different (for example, from liquid phase to gas phase), the opening pressure often changes. When the working temperature increases, the opening pressure generally decreases. Therefore, when it is adjusted at normal temperature and used at high temperature, the set pressure value at normal temperature should be slightly higher than the required opening pressure value. How high is related to the valve structure and material selection, and should be based on the manufacturer's instructions. ⑥ When the conventional safety valve is used to fix the additional back pressure, when the opening pressure is adjusted after the inspection (the back pressure is atmospheric pressure at this time), the setting value should be the required opening pressure value minus the additional back pressure value. 2. Adjustment of discharge pressure and reseating pressure of safety valve ① To adjust the discharge pressure and reseating pressure of the valve, the action test must be carried out to reach the full opening height of the valve. This is only possible after securing the device. The adjustment method varies according to the valve structure. ②For the structure with recoil disc and valve seat adjustment ring, the valve seat adjustment ring is used for adjustment. Unscrew the fixing screw of the adjustment ring, and extend a tool such as a thin iron rod from the exposed screw hole, and then the gear teeth on the adjustment ring can be toggled to make the adjustment ring rotate left and right. When the adjustment ring is rotated counterclockwise to the left, its position increases, and both the discharge pressure and the return pressure will decrease. Conversely, when the adjusting ring is rotated clockwise to the right, its position decreases, and both the discharge pressure and the return pressure will increase. Every time you adjust, adjust: the range of rotation of the circle should not be too large (generally, you can rotate a few teeth). After each adjustment, the fixing screw should be screwed on so that its end is located in the groove between the two teeth of the adjusting ring, which can not only prevent the adjusting ring from rotating, but also does not generate radial pressure on the adjusting ring. For the sake of safety, before turning the adjusting 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 an accident. ③For the structure with upper and lower adjustment rings (one adjustment ring on the guide sleeve and valve seat), the adjustment is more complicated. 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 when the valve is initially opened. When the valve seat adjustment ring is raised, the degree of pressure accumulation increases, so that the stage of proportional opening of the valve is reduced and the sudden rapid opening is achieved faster. Therefore, raising the seat adjustment ring can reduce the discharge pressure somewhat. It should be noted that the seat adjustment ring should not be raised too close to the disc. In that way, leakage at the sealing surface may cause the valve to open suddenly and prematurely, but because the medium pressure is not enough to keep the valve disc in the open position, the valve disc closes again, and the valve jumps frequently. Valve seat adjustment: 'The ring is mainly used to reduce the valve ratio, open the stage and adjust the discharge pressure, and also affect the return pressure. The upper adjusting ring is used to change the turning angle of the flowing medium after reflection on the underside of the valve disc, thereby changing the magnitude of the fluid force, thereby adjusting the seat pressure. When the upper adjusting ring is raised, the turning angle decreases, and the fluid force decreases accordingly, so that the return pressure increases. Conversely, when the upper adjusting ring is lowered, the reseating pressure decreases. certainly,When the upper adjusting ring changes the reseating pressure, it also affects the discharge pressure, that is, raising the upper adjusting ring will increase the discharge pressure, and lowering the upper adjusting ring will reduce the discharge pressure, but the effect is not as good as the reseating pressure. So obvious.