What are the inspection items for pneumatic diaphragm control valves?

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1. To check for leaks in the sealing packing and other connections, water at room temperature is introduced into one end of the control valve at a pressure equal to 1.1 times the nominal pressure of the valve or 1.5 times its maximum operating pressure; the other end is kept closed. The pressure is maintained for 10 minutes, during which time the valve stem moves back and forth 1 to 3 times per minute. There should be no leaks at the connections of the sealing stuffing box and other components. 2. Leakage inspection during shutdown ① For double-seat control valves, a simple water injection method can generally be used to check for leaks. Applying signal pressure to the diaphragm chamber causes the control valve to close (an input signal pressure of 1.2 kg/cm2 acts on air-actuated valves, while the signal pressure for air-operated valves is zero). Water at room temperature is injected at the inlet of the control valve; under no pressure, there should be no significant dripping at the other end. ② The hydraulic pressure method for checking leakage volume can be used for single-seat control valves, angle control valves, and diaphragm valves that are intended for emergency shutdown or require tight sealing. Applying signal pressure to the diaphragm chamber causes the control valve to close. Water at room temperature is fed into one end of the control valve under a constant pressure of 10 kg/cm2 in the direction that opens the valve core; the leakage rate at the other end is measured using a stopwatch and a measuring cup, and it should not exceed the allowable value. The formula for calculating the leakage rate: For single-seat control valves and angle control valves with a diameter of Dg≤3/4", a signal pressure is applied to the diaphragm chamber in order to close the valve. Compressed air at a pressure of 4 kg/cm2 is introduced into one end of the valve in a manner that opens the valve core; after the air supply is cut off, the pressure drop over a period of 3 minutes should be less than 0.15 kg/cm2.