Commonly used media for valve pressure test are water, oil, air, steam, nitrogen, etc. The pressure test methods for various valves are as follows.
(1) Strength test of globe valve and throttle valve stop valve and throttle valve, usually put the assembled valve in the pressure test frame, open the valve flap, inject the medium to the specified value, check whether the valve body and the valve cover are taken. Sweat and leaks. The strength test can also be carried out in one piece. The seal test is only used as a shut-off valve. During the test, the valve stem of the shut-off valve is in a vertical state, the valve flap is opened, the medium is introduced from the lower end of the valve flap to the specified value, and the packing and the gasket are inspected; after being qualified, the valve flap is closed, and the other end is opened to check for leakage. If both the valve strength and the tightness test are to be done, the strength test may be performed first, then the pressure is reduced to the specified value of the seal test, and the packing and the gasket are inspected; then the valve flap is closed, and the outlet end is opened to check whether the sealing surface leaks.
(2) Gate valve
The strength test of the gate valve is the same as that of the shut-off valve.
There are two methods for sealing the gate valve.
1 The shutter is opened to raise the pressure inside the valve to the specified value; then close the gate, immediately take out the gate valve, check whether there is leakage at the seal 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 is not suitable for sealing tests on gate valves with nominal diameters below DN32mm.
2 Another method is to open the shutter to raise the valve test pressure to the specified value; then close the shutter, open the blind plate at one end, and check whether the sealing surface leaks. Then go back and repeat the above test until it is qualified.
The seal test of the gate valve packing and gasket shall be carried out before the seal 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 tightness test: the valve is in a half-open state, one end is introduced into the test medium, and the other end is closed; the ball is rotated several times, the closed end is opened when the valve is closed, and the sealing performance at the packing and the gasket is checked. There must be no leakage. The test medium was then introduced from the other end and the above test was repeated.
2 Fixed ball valve tightness test: Before the test, the ball is idling several times, the valve is closed, the test medium is introduced from one end to the specified value; the pressure at the inlet is used to check the sealing performance of the inlet, and the accuracy of the pressure gauge is 0.5. ~1 level, the range is 1.6 times the test pressure. In the specified time, no depressurization is acceptable; then the test medium is introduced from the other end, and the above test is repeated. Then, the valve is in a half-open state, the ends are closed, the inner cavity is filled with the medium, and the packing and the gasket are inspected under test pressure, and there is no leakage.
3 Three-way ball valves should be tested for leaks at various locations.
(4) Plug valve
1 When the plug valve is tested for strength, the medium is introduced from one end, the remaining passages are closed, and the plugs are sequentially rotated to the fully open working positions for testing. No leakage is found in the valve body.
2 In the sealing test, the straight-type cock should keep the pressure in the cavity equal to the passage pressure, rotate the plug to the closed position, check from the other end, and then rotate the plug 180° to repeat the above test; three-way or four-way plug valve The pressure inside the chamber should be kept equal to the end of the passage. The plug should be rotated to the closed position in turn, the pressure is introduced from the right angle end, and the inspection is performed simultaneously from the other end. Before the plug valve test, a non-acid thin lubricating oil is allowed to be applied on the sealing surface, and no leaks and enlarged water droplets are found to be qualified within the specified time. The test time of the plug valve can be shorter, generally specified as 1 to 3 minutes 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 shut-off valve.
The sealing performance test of the butterfly valve shall be introduced into the test medium from the end of the medium flow. The disc shall be opened, the other end closed, and the injection pressure shall be the specified value. After checking the packing and other seals without leakage, close the disc and open the other end to check the butterfly. No leakage at the plate seal is acceptable. As a butterfly valve for regulating the flow rate, the sealing performance test may not be performed.
(6) Diaphragm valve
The diaphragm valve strength test introduces the medium from either end, opens the valve flap, and the other end is closed. After the test pressure rises to the specified value, the valve body and the valve cover are not leaked. Then, the pressure is reduced to the sealing test pressure, the valve flap is closed, and the other end is opened for inspection, and no leakage is acceptable.
(7) Check valve
Check valve test state: the lift check valve disc axis is in a position perpendicular to the horizontal; the swing check valve passage axis and the flap axis are in a position approximately parallel to the horizontal line.
In the strength test, the test medium is introduced from the inlet end to the specified value, and the other end is closed, and the valve body and the valve cover are not leaked.
The sealing test was introduced into the test medium from the outlet end. At the inlet end, the sealing surface was inspected, and no leakage at the packing and gasket was qualified.
(8) Safety valve
1 The strength test of the safety valve is the same as other valves and is tested with water. When the lower part of the valve body is tested, the pressure is introduced from the I=I end, and the sealing surface is closed. When the upper part of the valve body and the bonnet are tested, the pressure is introduced from the El end and the other ends are closed. The valve body and the valve cover have no leakage during the specified time.
2 Sealing test and constant pressure test, generally used medium: steam valve with saturated steam as test medium; ammonia or other gas valve with air as test medium; water and other non-corrosive liquid valves with water as test medium . For some important positions of safety valves, nitrogen is commonly used as the test medium.
The sealing test is carried out with the nominal pressure value as the test pressure, the number of which is not less than two, and no leakage is acceptable within the specified time. There are two kinds of leak detection methods: one is to seal the joints of the safety valve, and the thin paper is sealed on the El flange with butter, the tissue is bulged as a leak, and the bulge is not qualified; the second is to use a butter to thin The plastic plate or other plate is sealed on the lower part of the outlet flange, and the valve flap is filled with water to check that the water does not bubble.
The safety valve constant pressure and return pressure test times are not less than 3 times, and the requirements are qualified.
For the performance test of safety valve, see GB/T 12242--1989 ((Safety Valve Performance Test Method).
(9) Pressure reducing valve
1 The strength test of the pressure reducing valve is generally assembled after a single piece of test, and can also be tested after assembly. Strength test duration: DN 150 mm greater than 3 min.
After the bellows and the assembly are welded, the maximum pressure of the valve is applied 1.5 times and the strength test is performed with air.
2 The sealing test is carried out according to the actual working medium. When testing with air or water, the test is carried out at 1.1 times the nominal pressure; when using the steam test, the highest working pressure allowed at the operating temperature is carried out. The difference between the inlet pressure and the outlet pressure is not less than 0.2 MPa. The test method is as follows: after the inlet pressure is set, the adjusting screw of the valve is gradually adjusted, so that the outlet pressure can be sensitively and continuously changed within the range of maximum and minimum values, and there is no stagnation or jamming phenomenon. For the steam pressure reducing valve, when the inlet pressure is adjusted, the valve is closed after the valve is closed, and the outlet pressure is the highest and lowest values. Within 2 minutes, the outlet pressure should be increased in accordance with Table 4.176-22, and the valve behind the valve The volume meets the requirements specified in Table 4.18. 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 leak test, and no leakage is qualified within 2 minutes.
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