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Pressure test method for industrial valves

  • Author:Cowinns
  • Source:Cowinns
  • Release on :2020-02-07
Pressure test method for industrial valves

In general, industrial valves are not tested for strength when they are used, but after repair, the valve body and bonnet or corrosion-damaged valve body and bonnet should be tested for strength. For the safety valve, its constant pressure and return seat pressure and other tests shall meet the requirements of its instructions and relevant regulations. Before the valve is installed, the valve strength test and valve seal test should be performed on the valve hydraulic test bench. The low-pressure valve should be spot-checked at 20%. If it fails, it should be checked at 100%. The medium- and high-pressure valves should be checked at 100%. The commonly used media for valve pressure test are water, oil, air, steam, nitrogen, etc. The pressure test methods for various industrial valves including pneumatic valves are as follows:


Pressure test method of globe valve and throttle valve

     For the strength test of the shut-off valve and the 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. A single piece can also be used for strength testing. The tightness test is only done for globe valves. During the test, the valve stem of the shut-off valve is in a vertical state, the valve disc is opened, and the medium is introduced to the specified value from the bottom end of the valve disc. Check the packing and gasket; when it is qualified, close the valve disc and open the other end to check for leakage. If both the valve strength and tightness test are to be done, the strength test can be performed first, then the pressure is reduced to the specified value of the tightness test, and the packing and gasket are checked; then the valve flap is closed, and the outlet end is opened to check whether the sealing surface is leaking.


Pressure test method of gate valve

     The strength test of the gate valve is the same as that of the stop valve. There are two methods for the sealing test of the gate valve. ① The gate is opened so that the pressure in the valve rises to the specified value; then the gate is closed and the gate valve is immediately taken out to check whether there are leaks 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 ram. The above method is called intermediate pressure test. This method is not suitable for sealing tests on gate valves with a nominal diameter below DN32mm. ② Another method is to open the gate to increase the valve test pressure to the specified value; then close the gate and open the blind plate at one end to check whether the sealing surface is leaking. Turn down and repeat the test until it is qualified. The tightness test at the packing and gasket of the pneumatic gate valve shall be carried out before the tightness test of the gate.
     
  

Pressure test method of ball valve

   The strength test of the pneumatic ball valve should be carried out with the ball valve half open.

   ① Floating ball valve sealing test: Put the valve in a half-open state, introduce test medium at one end, and close the other end; rotate the ball several times, open the closed end when the valve is closed, and check the sealing performance at the same time as the filler and gasket. There must be no leakage. Then introduce the test medium from the other end and repeat the test.

   ② Sealing test of fixed ball valve: Before the test, rotate the ball several times with no load, the fixed ball valve is closed, and draw the test medium from one end to the specified value; check the sealing performance of the lead-in end with a pressure gauge, and use the accuracy of the pressure gauge to 0 .5 to 1 level, the range is 1.6 times the test pressure. Within the specified time, if there is no pressure drop, it is qualified; then introduce the test medium from the other end and repeat the above test. Then, the valve is in a half-open state, the two ends are closed, and the inner cavity is filled with the medium. Check the packing and gasket under the test pressure, and there must be no leakage.

③ The three-way ball valve should be tested for tightness at various positions.


Pressure test method of plug valve

   ① During the strength test of the plug valve, the medium is introduced from one end, the remaining passages are closed, and the plug is sequentially rotated to the fully opened working positions for testing. The valve body is qualified if no leakage is found.

  ② In the tightness test, the straight-through plug 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; The pressure in the cavity and the end of the passage should be kept equal, and the plugs should be rotated to the closed position in turn. The pressure is introduced from the right end and checked from the other end at the same time.

It is allowed to apply a layer of non-acid thin lubricating oil on the sealing surface before the plug valve test bench. No leakage or enlarged water droplets are found to be qualified within the specified time. The test time of the plug valve can be shorter, and it is generally 1-3 minutes according to the nominal diameter.

  Gas stopcocks shall be tested for air tightness at 1.25 times the working pressure.


Pressure test method of butterfly valve

     The strength test of pneumatic butterfly valve is the same as that of globe valve. The test of the butterfly valve's sealing performance should be introduced from the medium flowing end, 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 in the packing and other seals, close the butterfly plate, open the other end, and check the butterfly Passage without leakage at the plate seal is acceptable. The butterfly valve used to adjust the flow rate does not need to be tested for sealing performance. One kind Cowinns Viton lined butterfly valve has better function than metal to metal seated butterfly valve.


Pressure test method of diaphragm valve

     Diaphragm valve strength test. Introduce medium from either end, open the disc, and close the other end. After the test pressure rises to the specified value, it is acceptable to see that the valve body and valve cover have no leakage. Then reduce the pressure to the tightness test pressure, close the disc, open the other end for inspection, and no leakage is acceptable.


Pressure test method of check valve

     Check valve test status: The lift check valve flap axis is in a position perpendicular to the level; the swing check valve channel axis and the flap 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. It is acceptable to see that the valve body and valve cover have no leakage. For the leak test, the test medium is introduced from the outlet end, and the sealing surface is checked at the inlet end, and there is no leakage at the packing and gaskets.
     
     

Pressure test method of safety valve

①   The strength test of the safety valve, like other valves, such as ductile iron wafer butterfly valve is performed 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 valve cover, the pressure is introduced from the outlet El end, and the other ends are closed. The valve body and valve cover are qualified if there is no leakage within the specified time. ② Tightness test and constant pressure test, the commonly used medium is: steam safety valve with saturated steam as the test medium; ammonia or other gas valves with air as the test medium; water and other non-corrosive liquid valves with water as the test medium. Nitrogen is often used as the test medium for some important safety valves. For the sealing test, the nominal pressure value is used as the test pressure. The number of times is not less than two times, and no leakage is qualified within the specified time. There are two methods for leak detection: one is to seal the joints of the safety valve, and the thin paper is sealed on the El flange with butter. Plastic plates or other plates are sealed under the outlet flange, the valve flaps are filled with water, and it is qualified to check that there is no bubbling in the water. The safety valve constant pressure and back seat pressure test number of times is not less than 3 times, and it is qualified if it meets the regulations. For performance tests of safety valves, see GB / T 12242 "Test Methods for Safety Valve Performance".
     
     

Pressure test method of pressure reducing valve

     ① The strength test of the pressure reducing valve is generally assembled after a single test, and it can also be tested after assembly. Strength test duration: lmin for DN <50mm; greater than 2min for DN65 ~ 150mm; greater than 3min for DN> 150mm.

     After the bellows and the component are welded, the maximum pressure after applying the pressure reducing valve is 1.5 times, and the strength test is performed with air.

  ② The tightness test shall be carried out according to the actual working medium. When testing with air or water, the test is performed at 1.1 times the nominal pressure. When testing with steam, the test is performed at the maximum working pressure allowed at 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 be sensitively and continuously changed within the range of the maximum and minimum values ​​without stagnation or jamming. For steam pressure reducing valve, when the inlet pressure is adjusted, close the valve and close the valve. The outlet pressure is the highest and lowest value. Within 2 minutes, the increase in the outlet pressure should meet the requirements in Table 4.176-22. At the same time, the pipeline 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 adjusted and the outlet pressure is zero, the pressure reducing valve is closed to perform a leak test, and no leakage is qualified within 2 minutes.