Pressure test method of various valves - Wuzhong instrument

The commonly used medium for valve pressure testing is water, oil, air, steam, nitrogen, etc., and the pressure testing methods of various valves are as follows.

(1) Globe valve and throttle valve For the strength test of globe valve and throttle valve, the assembled valve is usually placed in the pressure test frame, the valve disc is opened, the medium is injected to the regular 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 experiment, the stem of the globe valve is straight, the disc is open, and the medium is introduced from the bottom end of the disc to the regular value, and the packing and gasket are checked; After passing the test, close the disc and open the other end to see if there is any 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 value of the tightness test rule, and the packing and gasket can be checked; Then close the disc and open the outlet to see if the sealing surface is leaking.

Pressure test method of various valves - Wuzhong instrument

Pressure test method of various valves - Wuzhong instrument

(2) Gate valves

The strength test of the gate valve is the same as that of the shut-off valve.

There are two ways to test the tightness of gate valves.

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

(2) Another method is to open the ram to raise the test pressure of the valve to the regular 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 above experiment until you are qualified.

The tightness test at the gate valve packing and gasket should be performed before the gate tightness test.

(3) Ball valves

The strength test of the ball valve should be carried out under the condition that the ball is half open.

(1) Floating ball valve tightness test: the valve is in a half-open state, one end is introduced into the experimental medium, and the other end is closed; Roll the ball several times, open the closed end when the valve is in a closed state, and check the sealing function at the packing and gasket together, and there shall be no leakage. Then the experimental medium is introduced from the other end,www.sypv.comRepeat the above experiment.

(2) Tightness test of fixed ball valve: before the experiment, roll the ball several times without load, and the valve is in a closed state, and lead the experimental medium to the regular value from one end; Use the pressure gauge to check the sealing function of the introduction end, and use the pressure gauge to have an accuracy of 0.5-1 level, and the range is 1.6 times of the experimental pressure. In the rules of the question, there is no blood pressure reduction phenomenon is qualified; Introduce the experimental medium from the other end and repeat the above experiment.

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 experimental pressure without leakage.

(3) Three-way ball valves should be tested for tightness in all directions.

(4) 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 full open operation direction for the experiment, 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 experiment; Three-way or four-way plug valves should keep the pressure in the chamber equal to one end of the path, rotate the plug in order to the closed position, and the pressure should be introduced from the right-angle end and viewed from the other ends.

Before the plug test, it was promised to apply a layer of non-acidic dilute lubricating oil on the sealing surface, and no leakage and enlarged water droplets were found within the specified time. The test time of the plug valve can be shorter, generally according to the nominal diameter rule of l-3min.

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

(5) Butterfly valve

The strength test of the butterfly valve is the same as that of the globe valve.

The sealing function test of the butterfly valve should introduce the experimental medium from the human end of the medium flow, the butterfly plate should be open, the other end should be closed, and the injection pressure should be to the regular value; After checking that there is no leakage in the packing and other seals, close the butterfly plate, turn over the other end, and check that there is no leakage in the sealing of the butterfly plate. As a butterfly valve for regulating the flow rate, it is not necessary to do a sealing function test.

(6) Diaphragm valve

The diaphragm valve strength test introduces the medium from either end, opens the valve disc, closes the other end, and after the experimental pressure rises to the regular value, see that the valve body and valve cover have no leakage to be qualified. 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) Check valve

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

During the strength test, the experimental medium is introduced from the inlet end to the regular value, and the other end is closed, and the valve body and valve cover are not leaked.

The sealing test introduces the experimental 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) Safety valve

(1) The strength test of the safety valve is the same as that of other valves, and the test is done with water. In the lower part of the experimental valve body, the pressure is introduced from the inlet I=I end, and the sealing surface is closed; In the upper part of the test body and bonnet, the pressure is introduced from the outlet end and the other ends are closed. If there is no leakage in the valve body and bonnet within the specified time, it is qualified.

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

The sealing test is carried out with the nominal pressure value as the experimental pressure, and the number of times is not less than two, and there is no leakage within the regular time is qualified. There are two ways to detect leakage: one is to seal the joints of the safety valve, and use butter to seal the tissue paper on the flange. 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 the compliance rules shall be qualified.

For the functional tests of the safety valve, please refer to GB/T 12242--1989 ((Safety Valve Functional Test Method).

(9) Pressure reducing valves

(1) The strength test of the pressure reducing valve is generally assembled after a single test, and it can also be assembled after the test. The duration of the intensity test is as follows: DN<50mm lmin, DN65-150mm more 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 behind the valve.

(2) The tightness test shall be carried out according to the actual operating medium. In the case of air or water experiments, the test is carried out at 1.1 times the nominal pressure, and in the case of steam test, the maximum operating pressure agreed at the operating temperature. The difference between the inlet pressure and the outlet pressure is not less than 0.2MPa. The experimental method is as follows: after the inlet pressure is adjusted, the conditioning screw of the valve is gradually adjusted, so that the outlet pressure can change sensitively and continuously within the maximum and minimum scales, and there shall be no stagnation and jamming. For the steam pressure reducing valve, when the inlet pressure is adjusted away, the outlet pressure is the highest and lowest value after the closed valve, and the value-added of the outlet pressure should conform to the rules in Table 4.176-22 within 2min, and the volume of the pipeline behind the valve is qualified in the rules in Table 4.18;

Pressure test method of various valves - Wuzhong instrument

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