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Pneumatic Diaphragm Control Valve inspection and verification

From:Net   Date:2011-6-7
Single Seat Pneumatic Diaphragm Control Valve is a production process technology automatically adjusts very important part of the system. In order to ensure their safe and normal operation of the installation or after maintenance before use should be based on the actual needs of the necessary checks and verification. 

Executive body checks

A film chamber tightness check 

When the signal pressure regulating valve nameplate range of 0.2 ~ 1kg/cm2 time (article below), will 0.8kg/cm2 pressure compressed air introduced into the film chamber, cut off the gas source, for 5 minutes, the film should not be gas chamber pressure drops Over 0.007kg/cm2 (5mmHg) T40H manual control valve.

2 putter movement and travel checks 

① with the range of 0 ~ 1kg/cm2 film chamber pressure input signal, increasing and decreasing signal pressure reciprocating the plunger moves should be uniform and flexible without catching jumps. 

② compression spring preload adjustment, when the signal pressure is 0.15kg/cm2 putter began to start (with modular instrumentation equipped with a start signal when pressure is 0.2kg/cm2). 

③ The pressure range of 0.2 ~ 1.0kg/cm2 signal pressure increase and decrease, putting stroke should meet the requirements regulating valve stroke. 

Inspection assembly 

A control valve assembly should be checked before valve, valve seat, stem or without defects. After grinding the valve with the valve seat should be tight, the stem should be straight is smooth. 

2 control valve and the actuator assembly, the film chamber input signal of the pressure regulating valve closed, adjust the length of the valve stem in close contact with the valve seat. Off valve for the gas input signal pressure 0.95kg/cm2, with modular instrumentation equipped with a time of 1.0 kg/cm2; gas valve open for input signal pressure is zero. Water rotary valve 

Check valve 

A sealing stuffing and other junction leakage checks 

The temperature of the water is room temperature to adjust the valve nominal pressure of 1.1 times or 1.5 times the maximum operating pressure of the pressure, to be fed in the direction to open the spool valve end, one closed end. Maintaining the pressure for 10 minutes at 1 per minute of the stem 3 to reciprocate. Stuffing box seals and other components connections should not be leakage.

2 Turn off the leak check

① water leak test method 

Generally available for valve seat simple method for detecting water leaks. Input signal to the film chamber pressure regulating valve is closed so that (air to close valve input 1.2kg/cm2 signal pressure, the gas valve open signal pressure is zero). Injected at the inlet valve of the water at room temperature, in the case of non-pressure side should be no other significant drip phenomenon.

② pressure method leakage checks

The accident cut off or require close tightly using a single-seat control valve, angle valve, diaphragm can use this method.

The input signal of the film chamber pressure to regulator valve is closed. The temperature of the water is room temperature, in order to open the valve at a constant pressure of 10kg/cm2 in the direction through the valve into one end of the measuring cup with a stopwatch and measured at the other end of the leakage should not exceed the allowable value. 

Formula for calculating the amount of leakage Where

 Q an allowable leakage (l / min)

C an ability to test the flow control valve

P - during the test pressure (kg/cm2), generally 10kg/cm2

A-allowed leak rate (%)

③ pressure leak test method

For Dg ≤ 3/4 "single-seat control valve, angle valve, air chamber to the film so that the input signal pressure regulating valve is closed, the pressure of 4kg/cm2 compressed air, press to open the way through into the spool valve end, cut off the gas source, for 3 minutes, the pressure drop should be less than 0.15kg/cm2.

Pneumatic control valve thin film checksum

Always check a point deviation

The film 0.2kg/cm2 input signal pressure gas chamber, and then increase the signal pressure to 1.0kg/cm2, the stem should take full stroke, and then reduce the signal pressure to 0.2 kg/cm2. In 1.0kg/cm2 and 0.2kg/cm2 stem travel is measured, the starting point and end point deviation deviation should not exceed the allowable value.

Two full-stroke deviation checksum 

The input signal pressure 0.2 kg/cm2 film chamber, and then increase the signal pressure to 1.0 kg/cm2, the stem should take full itinerary. Measuring whole trip deviation does not exceed the permissible value.

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