Pressure test methods for various valves

In general, industrial valves are not subject to strength test during use, but the repaired valve body and bonnet or the valve body and bonnet with corrosion damage shall be subject to strength test. For safety valves, the set pressure, reseating pressure and other tests shall comply with the specifications and relevant regulations. Strength and sealing test shall be conducted for the valve installation. 20% of the low-pressure valves shall be randomly inspected, and 100% of the valves shall be inspected if they are unqualified; Medium and high pressure valves shall be 100% inspected. The commonly used media for valve pressure test include water, oil, air, steam, nitrogen, etc. the pressure test methods for various industrial valves including pneumatic valves are as follows:

1 pressure test method of ball valve

The strength test of pneumatic ball valve shall be conducted when the ball is half open.

① Sealing test of floating ball valve: the valve shall be in the half open state, one end shall be introduced into the test medium, and the other end shall be closed; Turn the ball several times. When the valve is closed, open the closed end for inspection. At the same time, check the sealing performance of the packing and gasket. No leakage is allowed. Then introduce the test medium from the other end and repeat the above test.

② Sealing test of fixed ball valve: before the test, rotate the ball several times without load, the fixed ball valve is closed, and the test medium is introduced from one end to the specified value; Check the sealing performance of the lead-in end with a pressure gauge. The accuracy of the pressure gauge is 0.5 ~ 1 grade, and the measuring range is 1.5 times of the test pressure. If there is no pressure drop within the specified time limit, it is qualified; Then introduce the test medium from the other end and repeat the above test. Then, the valve shall be in the half open state, both ends shall be closed, and the inner cavity shall be filled with medium. Under the test pressure, the packing and gasket shall be checked to ensure no leakage.

③ Three way ball valves shall be tested for tightness at each position.

2 pressure test method of check valve

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

During the strength test, the test medium shall be introduced from the inlet end to the specified value, and the other end shall be closed. It is qualified if there is no leakage in the valve body and bonnet.

For the tightness test, the test medium is introduced from the outlet end, and it is qualified if there is no leakage at the sealing surface, filler and gasket at the inlet end.

3 pressure test method of pressure reducing valve

① The strength test of pressure reducing valve is generally assembled after single piece test, and it can also be tested after assembly. Strength test duration: lmin when dn<50mm; More than 2min for DN65 ~ 150mm; More than 3min for dn>150mm. After the bellows and components are welded, the strength test shall be conducted with air at 1.5 times the maximum pressure behind the pressure reducing valve.

② The sealing test shall be conducted according to the actual working medium. In case of air or water test, the test shall be conducted at 1.1 times the nominal pressure; The steam test shall be carried out at the maximum allowable working pressure under the working temperature. The difference between inlet pressure and outlet pressure shall not be less than 0.2MPa. The test method is as follows: after the inlet pressure is set, gradually adjust the adjusting screw of the valve to make the outlet pressure change sensitively and continuously within the range of maximum and minimum values, without stagnation and jamming. For the steam pressure reducing valve, when the inlet pressure is adjusted, close the block valve behind the valve, and the outlet pressure is the highest and lowest value. Within 2min, the appreciation of its outlet pressure shall comply with the provisions in table 4.176-22. At the same time, it is qualified if the volume of the pipeline behind the valve complies with the provisions in table 4.18; For water and air pressure reducing valves, when the inlet pressure is set and the outlet pressure is zero, close the pressure reducing valve for sealing test, and it is qualified if there is no leakage within 2min.

4 pressure test method of butterfly valve

The strength test of pneumatic butterfly valve is the same as that of stop valve. For the sealing performance test of butterfly valve, the test medium shall be introduced from the medium flow end, the butterfly plate shall be opened, the other end shall be closed, and the injection pressure shall reach the specified value; After checking that there is no leakage at the packing and other seals, close the butterfly plate, open the other end, and check that there is no leakage at the seal of the butterfly plate. The butterfly valve used for regulating flow may not be subject to sealing performance test.

5. Pressure test method of plug valve

① During the strength test of the plug valve, the medium shall be introduced from one end, the rest of the channels shall be closed, and the plug shall be rotated to the fully open working position in turn for the test. If no leakage is found in the valve body, it is qualified.

② During the sealing test, keep the pressure in the chamber equal to that in the passage, rotate the plug to the closed position, check from the other end, and then rotate the plug 180 ° to repeat the above test; The three-way or four-way plug valve shall keep the pressure in the chamber equal to that at one end of the passage, rotate the plug to the closed position in turn, introduce the pressure from the right angle end, and check from other ends at the same time.

Before the plug valve test, it is allowed to apply a layer of non acid thin lubricating oil on the sealing surface, and it is qualified if no leakage and expanded water drops are found within the specified time. The test time of plug valve can be shorter, which is generally 1 ~ 3min according to the nominal diameter.

The plug valve for gas shall be subject to air tightness test at 1.25 times the working pressure.

6 pressure test method of diaphragm valve

For the strength test of diaphragm valve, the medium is introduced from either end, the valve disc is opened, and the other end is closed. After the test pressure rises to the specified value, it is qualified if there is no leakage in the valve body and bonnet. Then reduce the pressure to the sealing test pressure, close the valve disc, open the other end for inspection, and it is qualified if there is no leakage.

7 pressure test method for stop valve and throttle valve

For the strength test of stop 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 specified value, and the valve body and bonnet are checked for sweating and leakage. The strength test can also be carried out on a single piece. The sealing test is only for the stop valve. During the test, the valve rod of the stop valve is vertical, the valve disc is opened, the medium is introduced from the lower end of the valve disc to the specified value, and the packing and gasket are checked; Close the valve disc after it is qualified, and open the other end to check whether there is leakage. If the strength and sealing test of the valve are required, the strength test can be conducted first, then the pressure can be reduced to the specified value of the sealing test, and the packing and gasket shall be checked; Then close the valve disc and open the outlet end to check whether the sealing surface leaks.

8 pressure test method for gate valve

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

① The ram is opened to raise the pressure in the valve to the specified value; Then close the ram, take out the gate valve immediately, check whether there is leakage at the seals on both sides of the ram, or directly inject the test medium into the plug on the bonnet to the specified value, and check the seals on both sides of the ram. The above method is called intermediate pressure test. This method is not suitable for sealing test on gate valves with nominal diameter below dn32mm.

② The other method is to open the ram to raise the valve test pressure to the specified value; Then close the ram, open the blind plate at one end, and check whether the sealing surface leaks. Repeat the above tests until they are qualified.

The sealing test at the packing and gasket of the pneumatic gate valve shall be conducted before the sealing test of the ram.

9 pressure test method of safety valve

① Like other valves, the strength test of safety valve is conducted 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 bonnet, the pressure is introduced from the outlet El end, and the other ends are closed. It is qualified if the valve body and bonnet have no leakage within the specified time.

② For the sealing test and constant pressure test, the commonly used medium is: saturated steam is used as the test medium for the 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. Nitrogen is often used as the test medium for safety valves at some important positions.