1. Appearance inspection
Valve body and sealing surface inspection
Observe whether there are sand holes, pores or cracks on the surface of the valve body, and check whether the connection between the valve body and the valve cover is tight to avoid external leakage risks;
Check the integrity of the sealing surface (such as rubber or copper material) to confirm that there is no aging, cracking or falling off. For soft sealing materials, the degree of wear should be paid special attention.
2. Static sealing test
Hydraulic pressure test
After closing the valve, connect it to the test pipe, inject clean water and pressurize it to 1.5 times the nominal pressure (such as PN10 valve pressurized to 15Bar), maintain the pressure for 10-15 minutes, and observe whether the pressure gauge is stable and leak-free;
Focus on checking the leakage of the flange connection, valve stem stuffing box and valve body corrosion area. Cast iron valve body needs to pay special attention to water seepage caused by sand holes.
Air pressure test
Use compressed air or nitrogen to pressurize to 1.1 times the nominal pressure, and detect the leakage point by applying soapy water, especially paying attention to the joint between the sealing surface and the valve body;
For scenes with higher requirements, a helium mass spectrometer can be used to detect small leaks (sensitivity up to 10^-6 mbar·L/s).
3. Dynamic performance test
Switch operation and leakage verification
Manually or electrically open and close the valve 50-100 times, and observe whether there is any medium residue after closing. The leakage rate should be ≤0.1% of the rated flow;
During the test, check whether the valve stem rotates smoothly. If the operating torque increases abnormally (such as DN50 valve>30N·m), it may indicate that the sealing surface is worn or the valve body is deformed.
Particle-containing medium simulation test
Circulate in a medium containing mud or suspended matter to verify the anti-scouring ability of the sealing surface. The soft sealing material (such as EPDM) of the cast iron ball valve should have no obvious scratches or damage.
IV. Special environment adaptability test
Corrosion resistance verification
Immerse the valve in a weak acid or salt spray environment for 48 hours, take it out and perform a water pressure test. The sealing performance should decrease by less than 10%;
Check whether the coating or anti-corrosion paint on the valve body is peeling off to avoid accelerated sealing failure.
Low temperature/humid heat cycle test
Carry out 5 rapid temperature change cycles in the temperature range of -10℃ to 80℃ to verify the adaptability of the sealing material to thermal expansion and contraction. The cast iron valve body needs to prevent micro cracks caused by temperature difference.
Qualification standards and maintenance recommendations
Conventional leakage rate: The pressure drop during the static test pressure maintenance period is ≤5%, and the dynamic test leakage is ≤0.1% of the flow rate;
Maintenance cycle: It is recommended to check the sealing surface every 6 months in a normal water quality environment, and shorten it to 3 months in a scene containing corrosive media;
Replacement threshold: Soft sealing materials must be replaced immediately when the wear depth is >0.5mm or the hardness decreases by >15%.
Note: Cast iron ball valves are not recommended for high pressure (> PN16) or strong corrosion conditions. The overall strength of the valve body and the matching of the sealing material must be evaluated simultaneously during inspection.