Pressure Testing Methods for Various Industrial Valves

Normally, industrial valves are not tested for strength in service, but after repair, body and bonnet or corrosion damaged body and bonnet should be tested for strength. For safety valves, their constant pressure and return pressure and other tests shall comply with their specifications and relevant regulations. Valve strength test and valve sealing test should be done on valve hydraulic test bench before valve installation. Low-pressure valves should be inspected 20% by random, 100% by unqualified, and 100% by medium and high-pressure valves. Water, oil, air, steam, nitrogen and other commonly used media for valve pressure test. The pressure test methods for various industrial valves with pneumatic valves are as follows:

1. Pressure Test Method of Globe Valve and Throttle Valve

Strength tests of globe and throttle valves usually place the assembled valves in the pressure test stand, open the disc, inject the medium to the specified value, and check whether the body and cover are sweating and leaking. Strength tests can also be carried out on a single piece. Sealing test is done only for globe valves. During the test, the stem of the globe valve is in a vertical state, the disc opens, the medium is introduced from the bottom of the disc to the prescribed value, and the filling and gasket are checked. When qualified, the disc is closed and the other end is opened to check whether there is leakage. If the strength and sealing test of the valve are to be done, the strength test can be done first, then the pressure can be lowered to the specified value of the sealing test to check the filler and gasket, and then close the valve disc, open the outlet to check whether the sealing surface is leaking.

2. Pressure Test Method of Gate Valve

The strength test of the gate valve is the same as that of the globe valve. There are two methods for sealing test of gate valves.

(1) The gate is opened to raise the pressure in the valve to the prescribed value; then close the gate and take out the gate valve immediately. Check whether there is leakage at the sealing points on both sides of the gate or inject test medium directly into the plug on the cover to the prescribed value, and check the sealing points on both sides of the gate. The above method is called intermediate pressure test. This method is not suitable for sealing test of gate valves with nominal diameter less than DN32mm.

Another method is to open the gate so that the test pressure of the valve rises to the specified value; then close the gate and open one end of the blind plate to check whether the sealing surface is leaking. Turn your head back and repeat the above tests until you are qualified.

The sealing test of filler and gasket of pneumatic gate valve should be carried out before the sealing test of gate.

3. Pressure Test Method of Ball Valve

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

(1) Sealability test of floating ball valve: the valve is in semi-open state, one end is introduced into test medium, the other end is closed; the ball is rotated several times, the valve is in closed state, the closed end is opened for inspection, and the sealing performance of filler and gasket is checked at the same time, no leakage is allowed. Then the test medium is introduced from the other end to repeat the experiment.

(2) Sealing test of fixed ball valve: before the test, the ball is rotated several times without load, and the fixed ball valve is in closed state, from one end of the test medium to the prescribed value; the sealing performance of the introduction end is checked by pressure gauge, the precision of which is 0.5-1 grade, and the measuring range is 1.6 times of the test pressure. Within the prescribed time limit, no hypotension phenomenon is qualified; then the test medium is introduced from the other end to repeat the above test. Then, the valve is in a semi-open state, both ends are closed, and the inner cavity is filled with medium. Under the test pressure, the filler and gasket should be inspected without leakage.

(3) Three-way ball valves should be tested for sealing at all positions.

4. Pressure Test Method of Cock Valve

When the strength test of the cock valve is carried out, the medium is introduced from one end, the other paths are closed, and the plugs are rotated to all working positions in turn. No leakage is found in the valve body to be qualified.

(2) In sealing test, the straight-through cock should keep the pressure in the cavity equal to that in the channel, rotate the plug to the closed position, check from the other end, and then rotate the plug 180 degrees to repeat the above test; the three-way or four-way cock valve should keep the pressure in the cavity equal to that at the one end of the channel, rotate the plug to the closed position in turn, and introduce the pressure from the right angle to the other end at the same time. Line check.

A non-acid thin lubricating oil is allowed on the sealing surface in front of the cock valve test bench. No leakage and enlarged water droplets are found within the specified time. The test time of the cock valve can be shorter. Generally, the nominal diameter is 1-3 minutes.

The cock valve for gas shall be tested for air tightness at a working pressure of 1.25 times.

5. Pressure Test Method of Butterfly Valve

The strength test of pneumatic butterfly valve is the same as that of globe valve. The sealing performance test of butterfly valve should introduce the test medium from the end of medium flow, the butterfly plate should be opened, the other end should be closed, and the injection pressure should reach the prescribed value; after checking the filler and other seals without leakage, close the butterfly plate, open the other end, and check that no leakage at the butterfly plate seal is qualified. Butterfly valves used to regulate flow can not be tested for sealing performance.

6. Pressure Test Method of Diaphragm Valve

The strength test of diaphragm valve introduces medium from either end, opens the disc, and closes the other end. When the test pressure rises to the specified value, the valve body and cover will be qualified without leakage. Then the pressure is lowered to the sealing test pressure, the valve disc is closed, the other end is opened for inspection, and no leakage is qualified.

7. Pressure Test Method of Check Valve

Check valve test status: lift check valve disc axis is perpendicular to the horizontal position; swing check valve channel axis and disc axis are approximately parallel to the horizontal position.

In the strength test, the test medium is introduced from the inlet end to the specified value, and the other end is closed to see that the valve body and cover are qualified without leakage.

Sealability test introduces test medium from the outlet, and inspects the sealing surface at the import end. No leakage at the filler and gasket is qualified.

8. Pressure Test Method of Safety Valve

The strength test of safety valve, like other valves, is done 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 valve body and the cover, the pressure is introduced from the outlet El end and the other ends are closed. No leakage of valve body and cover is qualified within the specified time.

(2) Sealing test and constant pressure test, generally using medium: steam safety valve with saturated steam as test medium; ammonia or other gas valves with air as test medium; water and other non-corrosive liquid valves with water as test medium. Nitrogen is commonly used as test medium for safety valves in some important positions.

The nominal pressure is used as the test pressure in the sealing test, and the next number is not less than two times. No leakage is qualified in the prescribed time. There are two methods for leak detection: one is to seal the joint of the safety valve, seal the thin paper on the El flange with butter, and the other is to seal the thin plastic plate or other plate on the lower part of the export flange with butter, and seal the valve disc with water to check that the water is not bubbling to be qualified. Safety valve constant pressure and return pressure test times not less than 3 times, meet the requirements for qualified.

The various performance tests of safety valves can be found in GB/T 12242-1989 safety valve performance test method.

9. Pressure Test Method of Pressure Reducing Valve

(1) The strength test of pressure relief valves is usually assembled after single-piece test or after assembly test. The duration of strength test was: lmin with DN < 50 mm; lmin with DN65 ~ 150 mm was more than 2 minutes; and lmin with DN > 150 mm was more than 3 minutes.

After the bellows and components are welded, the strength test is carried out with air at 1.5 times the maximum pressure after the pressure relief valve is applied.

(2) Sealing test shall be carried out according to the actual working medium. When tested with air or water, the test is carried out at 1.1 times the nominal pressure, and when tested with steam, at the maximum allowable working pressure at the working temperature. The difference between inlet pressure and outlet pressure is not less than 0.2 MPa. The test method is as follows: after adjusting the inlet pressure, the adjusting screw of the valve is gradually adjusted so that the outlet pressure can change sensitively and continuously in the range of maximum and minimum, without stagnation and blockage. For steam relief valves, when the inlet pressure is adjusted away, the outlet pressure of the shut-off valve is the highest and lowest. Within 2 minutes, the rise of the outlet pressure should be in accordance with Table 4.176-22. Meanwhile, the volume of the pipe behind the valve should be in accordance with Table 4.18. When the inlet pressure is adjusted and the outlet pressure is zero, the shut-off pressure relief valve should be sealed. The test shows that no leakage is qualified within 2 minutes.