Today, Xiaobian will introduce to you the pressure test method of industrial valves, the commonly used medium for valve pressure test is water, oil, air, steam, nitrogen, etc., and the pressure test methods of various industrial valves including pneumatic valves are as follows:

1. Pressure test method of globe valve and throttle valve

For the strength test of globe valves and throttle valves, the assembled valve is usually placed in a pressure test rack, the valve disc is opened, the medium is injected to the specified value, and the valve body and valve cover are checked for sweat and leakage. Strength tests can also be performed on a single piece. The tightness test is only done for the shut-off valve. During the test, the stem of the globe valve is in a vertical state, the valve disc is opened, the medium is introduced from the bottom of the valve disc to the specified value, and the packing and gasket are checked; After qualifying, close the valve disc and open the other end to check whether there is leakage. If the valve strength and tightness test are to be done, the strength test can be done first, and then the pressure can be lowered to the specified value of the tightness test, and the packing and gasket can be checked; Then close the disc and open the outlet to check whether the sealing surface is leaking.

2. Pressure test method of gate valve

The strength test of gate valves is the same as that of shut-off valves. There are two methods for the tightness test of gate valves.

(1) The ram is opened, so that the pressure in the valve rises to the specified value; Then close the gate, immediately take out the gate valve, check whether there is leakage at the seals on both sides of the gate or directly inject the test medium into the plug on the valve cover to the specified value, and check the seals on both sides of the gate. The above method is called intermediate pressure test. This method is not suitable for sealing test in gate valves with nominal diameter below DN32mm.

(2) Another method is to open the ram to raise the valve test pressure to the specified value; Then close the gate, open the blind plate at one end, and check whether the sealing surface is leaking. Then turn your head and repeat the test until you are qualified.

The tightness test at the packing and gasket of the pneumatic gate valve should be carried out before the gate tightness test.

3. Pressure test method of ball valve

The strength test of the pneumatic ball valve should be carried out in the semi-open state of the ball.

(1) Floating ball valve tightness test: the valve is in a half-open state, one end is introduced into the test medium, and the other end is closed; Turn the ball several times, open the closed end when the valve is closed, and check the sealing performance of the packing and gasket at the same time, and there shall be no leakage. Then introduce the test medium from the other end and repeat the above test.

(2) Tightness test of fixed ball valve: rotate the ball several times without load before the test, and the fixed ball valve is in a closed state, and the test medium is led to the specified value from one end; Use a pressure gauge to check the sealing performance of the inlet end, and use the pressure gauge with an accuracy of 0.5~1 grade, and the range is 1.6 times of the test pressure. Within the specified question, there is no blood pressure reduction phenomenon is qualified; Then introduce the test medium from the other end and repeat the above test. Then, the valve is in a half-open state, both ends are closed, the inner cavity is filled with medium, and the packing and gasket are checked under the test pressure without leakage.

(3) Three-way ball valves should be tested for tightness in various positions.

4. Pressure test method of plug valve

(1) When the plug valve is tested for strength, the medium is introduced from one end, the rest of the channels are closed, and the plug is rotated to the fully open working position in turn for the test, and the valve body is qualified if no leakage is found.

(2) During the tightness test, the straight-through should keep the pressure in the cavity and the passage equal, rotate the plug to the closed position, check it from the other end, and then rotate the plug 180° to repeat the above test; Three-way or four-way plug valves should keep the pressure in the chamber equal to one end of the path, rotate the plug to the closed position in turn, and the pressure is introduced from the right-angle end, and the other ends are checked at the same time.

A layer of non-acidic dilute lubricating oil is allowed to be applied on the sealing surface in front of the plug valve test bench, and no leakage and enlarged water droplets are found within the specified time. The test time of the plug valve can be shorter, and it is generally l~3min according to the nominal diameter.

The plug valve for gas should be tested for air tightness at 1.25 times the working pressure.

5. Pressure test method of butterfly valve

The strength test of pneumatic butterfly valves is the same as that of globe valves. The sealing performance test of the butterfly valve should be introduced into the test medium from the human end of the medium flow, the butterfly plate should be opened, the other end should be closed, and the injection pressure should be reached the specified value; After checking that there is no leakage in the packing and other seals, close the butterfly plate, open the other end, and check that there is no leakage in the seal of the butterfly plate. Butterfly valves used to regulate flow rates do not need to be tested for sealing performance.

6. Pressure test method of diaphragm valve

The diaphragm valve strength test introduces the medium from either end, opens the valve disc, closes the other end, and after the test pressure rises to the specified value, the valve body and the valve cover are qualified to see that there is no leakage. Then the pressure is lowered to the tightness test pressure, the valve disc is closed, and the other end is opened for inspection, and no leakage is qualified.

7. Pressure test method of check valve

Check valve test status: the axis of the valve disc of the lifting check valve is in a position perpendicular to the horizontal; The swing-off check valve channel axis and disc axis are approximately parallel to the horizontal line.

During the strength test, the test medium is introduced from the inlet end to the specified value, and the other end is closed, and the valve body and valve cover are qualified to see that there is no leakage.

The tightness test introduces the test medium from the outlet end, and the sealing surface is checked at the inlet end, and there is no leakage at the packing and gasket to be qualified.

8. Pressure test method of safety valve

(1) The strength test of the safety valve is the same as that of other valves, which is tested with water. When testing the lower part of the valve body, the pressure is introduced from the inlet I=I end, and the sealing surface is closed; When testing the upper part of the body and bonnet, the pressure is introduced from the outlet end and the other ends are closed. No leakage of the valve body and bonnet within the specified time is qualified.

(2) For tightness test and constant pressure test, the general medium used is: saturated steam is used as the test medium for steam safety valve; Valves for ammonia or other gases use air as the test medium; Valves for water and other non-corrosive liquids use water as the test medium. For safety valves in some important positions, nitrogen is often used as the test medium.

The sealing test is carried out with the nominal pressure value as the test pressure, and the number of times is not less than two, and no leakage within the specified time is qualified. There are two ways to detect leakage: one is to seal the connections of the safety valve, seal the tissue paper with butter on the flange, and the tissue paper is bulging for leakage, and not bulging for qualification; The second is to use butter to seal the thin plastic plate or other plates in the lower part of the outlet flange, fill the water to seal the valve disc, and check that the water does not bubble to be qualified. The number of constant pressure and return pressure tests of the safety valve shall not be less than 3 times, and it shall be qualified if it meets the regulations.

For the performance test of the safety valve, please refer to GB/T 12242–1989 Safety Valve Performance Test Method.

9. Pressure test method of pressure reducing valve

(1) The strength test of the pressure reducing valve is generally assembled after the single piece test, and the test can also be carried out after assembly. Duration of strength test: DN<50mm lmin; DN65~150mm is greater than 2min; DN>150mm >3min.

After the bellows is welded to the component, the strength test is carried out with air at 1.5 times the maximum pressure after applying the pressure reducing valve.

(2) The tightness test shall be carried out according to the actual working medium. The test is carried out at 1.1 times the nominal pressure in the case of air or water test, and the maximum allowable working pressure at operating temperature in the case of steam test. The difference between the inlet pressure and the outlet pressure is not less than 0.2MPa. The test method is as follows: after the inlet pressure is adjusted, gradually adjust the adjusting screw of the valve, so that the outlet pressure can change sensitively and continuously within the range of the maximum and minimum values, and there shall be no stagnation and jamming. For the steam pressure reducing valve, when the inlet pressure is adjusted away, the valve is cut off after the valve is closed, the outlet pressure is the highest and lowest value, within 2min, the appreciation of the outlet pressure should be in accordance with the provisions of Table 4.176-22, at the same time, the volume of the pipeline behind the valve is qualified in accordance with the provisions of Table 4.18;