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Views: 33 Author: Amy Xiong Publish Time: 2024-11-14 Origin: www.wktipvf.com
Under normal circumstances, the strength test of the valve body is not performed when industrial valves are in use, but the body and valve cover after repair or the valve body and valve cover damaged by corrosion should be subjected to strength test. For safety valves, their constant pressure, backseat pressure and other tests should be strength tested. Comply with its instructions and related procedures. Before the valve is installed, the valve strength test and valve sealing test should be conducted on the valve hydraulic test bench. 20% of low-pressure valves shall be randomly inspected. If they are unqualified, 100% shall be inspected; medium and high-pressure valves shall be 100% inspected. Commonly used media include water, oil, air, steam, nitrogen, etc. Mainstream industrial valves include pressure testing methods for pneumatic valves. as follows:
To conduct strength tests on valves and throttles,usually place the completed valve in a pressure test stand, open the valve,inject the medium to the specified value, and check whether the valve body and valve cover are sweating or leaking.Strength testing can also be performed on a single piece.The sealing test only involves one valve.During the test,the designated valve stem is in a vertical state, the valve disc is opened, and the medium is introduced from the bottom of the valve disc to the specified value in sequence.Check the gasket and gasket; close the valve after passing the test.If the valve strength and sealing tests are required, You can do a strength test first, then reduce the pressure to the specified value for the sealing test,and check the circuit and gasket; then close the valve and open the outlet end to check whether the sealing surface is leaking.
The strength test of gate valves is the same as that of stop valves. There are two methods for industrial gate valve sealing test.
Open the gate to raise the pressure in the valve 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 is not suitable for sealing tests on gate valves with nominal diameters below DN32mm.
Another method is to open the gate to raise the test pressure of the valve 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 the head down and repeat the above test until it is qualified. The sealing test of the pneumatic gate valve packing and gasket should be carried out before the gate sealing test.
When conducting the strength test for pneumatic ball valves, it is essential to perform the test with the ball positioned at a semi-open state.
For floating ball valve sealing test: Place the valve in a semi-open state, insert the test medium into one end, and close the other end. Rotate the ball multiple times and open the closed end while closing the valve. During this process, inspect the sealing effectiveness of the packing and gasket. There should be no leaks. Then, inject the test medium from the other end and repeat the same test.
For fixed ball valve sealing test: Rotate the ball several times until it's in a no-load state, then close the fixed ball valve. Introduce the test medium from one end to the specified pressure level and employ a pressure gauge with an accuracy of 0.5 - 1 and a measurement range of 1.6 times the test pressure to evaluate the sealing efficiency at the inlet end. If there is no decompression within the specified time frame, the valve is considered qualified. Subsequently, inject the test medium from the other end and repeat the test.
To further assess the sealing integrity, place the valve in a half-open state, close both ends, and fill the inner cavity with the medium. This allows for an examination of the packing and gaskets under the test pressure, and there should be no leakage.
The strength test of the pneumatic butterfly valve is the same as that of the globe control valve. The sealing performance test of the butterfly valve should introduce the test medium from the medium inflow 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 at the packing and other seals, close the butterfly plate, open the other end, and check the butterfly plate It is qualified if there is no leakage at the seal. Butterfly valves used to regulate flow may not be tested for sealing performance.
Test status of the check valve:the disc axis of the lift check valve is in a position perpendicular to the horizontal;the channel axis and disc axis of the swing check valve 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 there is no leakage from the valve body and bonnet.In the tightness test,the test medium is introduced from the outlet end,and the sealing surface is checked at the inlet end. If there is no leakage at the packing and gasket,it is qualified.
The medium is inserted from one end during the strength test of the plug valve,the other passages are closed,and the plug is turned to fully open working position for the test.If there is no leakage, then the valve body qualifies.At the time of the sealing test,the straight-through cock must maintain the pressure in the cavity similar to that of the passage,turn the plug to the closed position,inspect from the other end,and then turn the 180 ° plug to repeat the above test;the three-way or four-way plug valve.Pressure in the cavity and one end of the passage should be maintained at the same time, the plugs should be turned to the closed position, the pressure from the right-angle end,as well as the other end,should be examined at the same time.Stop the test bench before allowing the sealing surfaces coated with a non-acid dilute lubricant to be sealed within a predetermined time without leaking and the expansion of the water droplets is permissible.The test time of the plug valve may be shorter, normally 1~3min depending on the nominal diameter.The gas plug valve shall be checked for airtightness at 1.25 times the operating pressure.
The diaphragm valve strength test introduces medium from either end, opens the valve disc, and closes the other end.After the test pressure rises to the specified value,the valve body and valve cover are deemed to be qualified if there is no leakage.Then reduce the pressure to the sealing test pressure,close the valve disc,and open the other end for inspection. If there is no leakage,it is qualified.
The strength test of the safety valve is the same as that of other valves, using 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 testing the upper part of the valve body and valve cover, the pressure is introduced from the outlet end and the other ends are closed. The valve body and valve cover are deemed to be qualified if there is no leakage within the specified time.
For sealing tests and constant pressure tests, the generally used media are: safety valves for steam use saturated steam as the test medium; valves for ammonia or other gases use air as the test medium; valves for water and other non-corrosive liquids use water as the test medium . Nitrogen is commonly used as the test medium for safety valves in some important locations.
The sealing test shall be carried out with the nominal pressure value as the test pressure, and the number of tests shall be no less than twice. If there is no leakage within the specified time, it shall be deemed as qualified. There are two methods of leak detection: one is to seal the joints of the safety valve, and use butter to seal the tissue paper on the outlet flange. If the tissue paper bulges, it is a leak, and if it does not bulge, it is qualified; the other is to use butter to seal the thin paper. A plastic plate or other plate seal is attached to the lower part of the outlet flange, and water is poured into the valve to seal it. If there is no bubbling in the water, it is considered qualified. The number of constant pressure and backseat pressure tests of the safety valve shall be no less than 3 times, and it shall be considered qualified if it meets the regulations.For various performance tests of safety valves, please refer to GB/T 12242-1989 Safety Valve Performance Test Methods.
The strength test of the pressure reducing valve is generally performed as a single piece before assembly, or it can also be tested after assembly. Strength test duration: 1min for DN<50mm; more than 2min for DN65~150mm; more than 3min for DN>150mm.
After the bellows and components are welded, the strength test should be conducted with air at 1.5 times the maximum pressure after the pressure reducing valve.
The sealing 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 allowable working pressure at the operating 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 set, gradually adjust the adjusting screw of the valve so that the outlet pressure can change sensitively and continuously within the maximum and minimum range without stagnation or jamming. For the steam pressure reducing valve, after the inlet pressure is adjusted away, the valve is closed and the valve is cut off. The outlet pressure is the highest and lowest value. Within 2 minutes, the increase in outlet pressure should comply with the requirements in Table 4.176-22. At the same time, the pipeline behind the valve If the volume meets the requirements in Table 4.18, it is qualified; for water and air pressure reducing valves, when the inlet pressure is adjusted and the outlet pressure is zero, close the pressure reducing valve and conduct a sealing test. If there is no leakage within 2 minutes, it is qualified.
