Pressure test methods for check valve safety valve pressure reducing valve

01. Pressure test method for check valve

Test state of the check valve: the axis of the lift check valve is at a position perpendicular to the horizontal; the axis of the swing check valve and the axis of the flap are approximately parallel to the horizontal.

In the strength test, the test medium is introduced from the inlet end to the specified value, and the other end is closed, check the valve body and the valve cover. If there is no leakage, it is qualified.

The sealing test is to introduce the testing medium from the outlet end, and to check the sealing surface, packing and gasket at the inlet end. If there is no leakage, it is qualified.

Pressure test methods for check valve safety valve pressure reducing valve

02. Pressure test method for safety valve

① The strength test of the safety valve is the same as other valves and is tested with water. When testing the lower part of the valve body, the pressure is introduced from the inlet end, and the sealing surface is closed; when the upper part of the valve body and the valve cover are tested, the pressure is introduced from the outlet end, and the other ends are closed. If the valve body and the valve cover have no leakage during the specified time, it is qualified.

② For the sealing test and constant pressure test, the general medium used is:  steam safety valve with saturated steam as test medium; ammonia or other gas valve with air as test medium; water and other non-corrosive liquid valves use water as the test medium. For some safety valves in important positions, 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 methods for leak detection: one is to seal the joints of the safety valve, and a piece of thin paper is sealed on the outlet flange with butter. If the thin paper is swelled, there is leakage and it is not quatified. If not, then it is qualified. The second is to seal the thin plastic plate or other plate with butter on the lower part of the outlet flange, fill the valve flap with water, and check that the water does not bubble. If there is no bubble, it is qualified. The safety valve constant pressure and return pressure test times are not less than 3 times. If it meets the requirements, it is qualified.

For the performance test of the safety valve, please refer to GB/T 12242–1989 Safety Valve Performance Test Method.

03. Pressure test method for pressure reducing valve

① The strength test of the pressure reducing valve is generally carried out in a single piece, and then assemble them.  It can also be tested after assembly. Duration time of the strength test: l min for pressure reducing valve of DN<50 mm; more than 2 min for pressure reducing valve of DN65-150 mm; more than 3 min for DN>150 mm.

After the bellows and the other components are welded, the strength test should be carried out with air at a pressure of 1.5 times the maximum pressure of the pressure reducing valve.

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 testing with steam, it is carried out at the highest working pressure allowed at the operating temperature. 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, after the inlet pressure is adjusted, close the shut off valve behind. The outlet pressure is the highest and lowest. Within 2 min, the rise of the outlet pressure should meet the requirements in Table 4.176-22. At the same time, the volume of the pipe after the valve meets the requirements specified in Table 4.18. For the water and air pressure reducing valve, when the inlet pressure is set and the outlet pressure is zero, the pressure reducing valve is closed for the leak test, and no leakage is qualified within 2 minutes.

 
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