Before the valve is installed, the valve strength test and valve sealing test should be performed on the valve hydraulic test bench. 20% of low-pressure valves should be inspected randomly, and 100% should be inspected if they are unqualified; 100% of medium and high-pressure valves should be inspected. The commonly used media for valve pressure testing are water, oil, air, steam, nitrogen, etc. The pressure testing methods for industrial valves including pneumatic valves are as follows:
Butterfly valve pressure test method
The strength test of the pneumatic butterfly valve is the same as that of the globe valve. In the sealing performance test of the butterfly valve, the test medium should be introduced from the flow end of the medium, the butterfly plate should be opened, the other end should be closed, and the injection pressure should 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 the butterfly valve. No leakage at the plate seal is qualified. Butterfly valve used for regulating flow may not be tested for sealing performance.
Pressure test method of check valve
Check valve test state: the axis of the lift check valve disc is in a position perpendicular to the horizontal; the axis of the swing check valve channel and the disc axis are in a position approximately parallel to the horizontal line.
During the strength test, the test medium is introduced from the inlet to the specified value, and the other end is closed, and it is qualified to see that the valve body and valve cover have no leakage.
In the sealing test, the test medium is introduced from the outlet end, and the sealing surface is checked at the inlet end, and no leakage at the packing and gasket is qualified.
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 the tightness test of the gate valve.
① Open the gate to make the pressure in the valve rise to the specified 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 test medium into the plug on the valve cover to the specified value , check the seals on both sides of the gate. The above method is called intermediate pressure test. This method should not be used for sealing tests on gate valves with a nominal diameter below DN32mm.
② Another method is to open the gate to make the valve test pressure rise to the specified value; then close the gate, open one end of the blind plate, and check whether the sealing surface is leaking. Then turn back and repeat the above test until it is qualified.
The tightness test of the packing and gasket of the pneumatic gate valve shall be carried out before the tightness test of the gate.
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 can also be tested after assembly. Duration of strength test: 1min for DN<50mm; more than 2min for DN65～150mm; more than 3min for DN>150mm.
After the bellows and components are welded, apply 1.5 times the maximum pressure of the pressure reducing valve, and conduct a strength test with air.
② The airtightness test shall be carried out according to the actual working medium. When testing with air or water, test at 1.1 times the nominal pressure; when testing with steam, use the maximum working pressure allowed under the working temperature. The difference between the inlet pressure and the outlet pressure is required to be not less than 0.2MPa. The test method is: 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, without stagnation or jamming. For the steam pressure reducing valve, when the inlet pressure is adjusted away, the valve is closed after the valve is closed, and the outlet pressure is the highest and lowest values. Within 2min, the increase in the outlet pressure should meet the requirements in Table 4.176-22. At the same time, the pipeline behind the valve should be The volume conforms to the requirements in Table 4.18 to be qualified; for water and air pressure reducing valves, when the inlet pressure is set and the outlet pressure is zero, the pressure reducing valve is closed for a tightness test, and no leakage within 2 minutes is qualified.
Pressure test method for 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 specified value, and the valve body and valve cover are checked for sweat and leakage. The strength test can also be carried out on a single piece. The tightness test is only for the shut-off valve. During the test, the valve stem of the globe valve is in a vertical state, the valve disc is opened, the medium is introduced from the bottom end of the valve disc to the specified value, and the packing and gasket are checked; after passing the test, the valve disc is closed, and the other end is opened to check whether there is leakage. If the strength and tightness test of the valve are to be done, the strength test can be done first, then the pressure is reduced to the specified value of the tightness test, and the packing and gasket are checked; then the valve disc is closed, and the outlet end is opened to check whether the sealing surface is leaking.
Ball valve pressure test method
The strength test of the pneumatic ball valve should be carried out in the half-open state of the ball valve.
① Floating ball valve sealing test: put the valve in a half-open state, introduce the test medium at one end, and close the other end; rotate the ball several times, open the closed end when the valve is in the closed state, and check the sealing performance at the packing and gasket at the same time. There should be no leakage. The test medium is then introduced from the other end and the above test is repeated.
② Sealing test of the fixed ball valve: before the test, rotate the ball several times without load, the fixed ball valve is in the closed state, and the test medium is introduced from one end to the specified value; the sealing performance of the introduction end is checked with a pressure gauge, and the accuracy of the pressure gauge is 0 .5 to 1, the range is 1.6 times the test pressure. Within the specified time, if there is no depressurization phenomenon, it is qualified; then introduce the test medium from the other end, and repeat the above test. Then, put the valve in a half-open state, close both ends, and fill the inner cavity with the medium. Check the packing and gasket under the test pressure, and there must be no leakage.
③ The three-way ball valve shall be tested for tightness at each position.
Post time: Mar-02-2022
