Precautions when adjusting the opening pressure of a safety valve

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When adjusting the opening pressure, the following points should be taken into account: When the medium pressure approaches the opening pressure (reaching over 90% of the opening pressure), the adjustment screw should not be rotated, to prevent the valve disc from rotating as well and thus damaging the sealing surface. 　　　To ensure the accuracy of the opening pressure value, the medium conditions used for adjustment, such as the type of medium and its temperature, should be as close as possible to the actual operating conditions. The opening pressure often changes when the type of medium changes, especially when transitioning from a liquid phase to a gas phase. As the operating temperature increases, the opening pressure decreases. Therefore, when it is adjusted at normal temperature for use at high temperatures, the set pressure value at normal temperature should be slightly higher than the opening pressure value required. Adjustment of discharge pressure and return pressure 　　　 After the opening pressure has been adjusted, if the discharge pressure or return pressure does not meet the requirements, the adjustment ring on the valve seat can be used for fine-tuning. Unscrew the fixing screw of the adjustment ring, insert a tool such as a thin iron rod into the exposed screw hole, and this will allow you to move the teeth on the adjustment ring, causing it to rotate left and right. When the adjustment ring rotates to the right in a counterclockwise direction, its position rises, and both the discharge pressure and the return pressure decrease ； Conversely, when the adjusting ring rotates clockwise to the left, its position drops, and both the discharge pressure and the return pressure increase. With each adjustment, the rotation amplitude of the adjusting ring should not be too large (generally within 5 teeth). After each adjustment, the set screw should be tightened so that its tip sits in the groove between the two teeth of the adjustment ring, thereby preventing the ring from rotating; however, no lateral pressure should be applied to the adjustment ring. Then, a movement test is conducted. For safety reasons, before adjusting the control ring, the pressure at the inlet of the safety valve should be reduced appropriately (generally to less than 90% of the opening pressure) to prevent the valve from opening suddenly during adjustment and causing an accident. 　　　It must be noted that conducting tests on the discharge pressure and seat-back pressure of safety valves is only possible when the flow rate from the gas source is high enough to prevent the valve from opening (i.e., when the rated discharge capacity of the safety valve is reached). Moreover, the test benches commonly used to verify the opening pressure of safety valves have very limited capacity; in such cases, the valve cannot be opened fully, and its return pressure is also inaccurate. When calibrating the opening pressure on such a test bench, in order to make the starting action more noticeable, the adjustment ring is usually set at a relatively high position; however, this is not appropriate under the actual operating conditions of the valve, and it is necessary to readjust the position of the adjustment ring. Sealing 　　　After all adjustments to the safety valve have been completed, it should be sealed to prevent any unauthorized changes to the adjusted settings. When leaving the factory, safety valves are usually adjusted using ambient air at the upper limit of the working pressure rating (i.e., high pressure), unless otherwise specified. Therefore, users generally need to make adjustments based on the actual working conditions. Then re-seal it with lead.