The commonly used media for valve pressure test are water, oil, air, steam, nitrogen, etc. The pressure test 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 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.
(2) 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 test pressure of the valve 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 sealing test of the gate valve packing and gasket shall be carried out before the sealing test of the gate.
(3) Ball valve
The strength test of the ball valve should be carried out with the ball half-open.
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 fixed ball valve: before the test, rotate the ball several times with no load, the valve is in the closed state, and introduce the test medium from one end to the specified value; use a pressure gauge to check the sealing performance of the lead-in end, and the accuracy of the pressure gauge is 0.5 ~1 level, 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.
(4) Plug valve
① When the strength test of the plug valve is carried out, the medium is introduced from one end, the other passages are closed, and the plug is rotated to the fully open working positions for the test, and the valve body is qualified if no leakage is found.
② During the sealing test, the straight-through plug should keep the pressure in the cavity equal to that of the passage, rotate the plug to the closed position, check from the other end, and then repeat the above test by rotating the plug 180°; three-way or four-way plug valve The pressure in the cavity and one end of the passage should be kept equal, the plugs should be rotated to the closed position in turn, the pressure should be introduced from the right-angle end, and the other ends should be checked at the same time.
Before the plug valve test, it is allowed to apply a layer of non-acid dilute lubricating oil on the sealing surface, and it is qualified if no leakage and enlarged water droplets are found within the specified time. The test time of the plug valve can be shorter, generally 1 ~ 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) Butterfly valve
The strength test of the 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 inflow 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 plate No leakage at the seal is qualified. Butterfly valve used for regulating flow may not be tested for sealing performance.
(6) Diaphragm valve
Diaphragm valve strength test: The medium is introduced from either end, the valve flap is opened, and the other end is closed. After the test pressure rises to the specified value, it is qualified to see that the valve body and bonnet have no leakage. Then reduce the pressure to the tightness test pressure, close the valve disc, and open the other end for inspection, if there is no leakage, it is qualified.
(7) 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 end 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.
(8) Safety valve
① The strength test of the safety valve is the same as 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 valve body and the bonnet, the pressure is introduced from the outlet El end, and the other ends are closed. If the valve body and bonnet have no leakage within the specified time, it is qualified.
② For the sealing test and constant pressure test, the general use medium is: the steam valve uses saturated steam as the test medium; the valve for ammonia or other gases uses air as the test medium; the valve for water and other non-corrosive liquids uses water as the test medium . Nitrogen is often used as the test medium for safety valves in some important positions.
The sealing test is carried out with the nominal pressure value as the test pressure, and the number of times is not less than twice, and no leakage within the specified time is qualified. There are two leak detection methods: one is to seal the joints of the safety valve, and use butter to seal the tissue paper on the flange. The plastic plate or other plate is sealed on the lower part of the outlet flange, and the valve disc is sealed by filling with water, and it is qualified if the water does not bubble.
The number of constant pressure and reseating pressure tests of the safety valve is not less than 3 times, and compliance with the regulations is qualified.
For the performance tests of safety valves, see GB/T 12242–1989 ((Test methods for performance of safety valves).
(9) 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: more than 3min for DN150mm.
After the bellows and the components are welded, apply 1.5 times the higher pressure behind the 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 higher 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 larger and smaller values, without stagnation or jamming. For the steam pressure reducing valve, when the inlet pressure is adjusted away, the valve is shut off after the valve is closed, and the outlet pressure is higher and lower. The volume of the rear pipeline meets the requirements in Table 4.18 to be qualified; for the 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.