Commonly used media for valve pressure testing include water, oil, air, steam, and nitrogen. The following are the standard methods for conducting pressure tests on different types of valves:
(1) **Globe Valve and Throttle Valve**: During the strength test, the fully assembled valve is placed in a testing frame. The valve is opened, and the medium is introduced to the specified pressure level. The valve body and cover are checked for leaks or sweating. For the seal test, the valve stem should be vertical, and the medium is injected from the bottom of the valve disc. After confirming no leakage, the disc is closed, and the other end is opened to check for any seepage. If both strength and tightness tests are required, the strength test is done first, followed by reducing the pressure to the sealing test level, then checking the packing and gaskets again before closing the disc and inspecting the sealing surface.
(2) **Gate Valve**: The strength test for gate valves is similar to that of shut-off valves. There are two main methods for the seal test: - Method 1: Open the gate, increase the internal pressure to the required level, close the gate, remove the valve, and check for leakage on both sides. This is called the intermediate pressure test, but it's not suitable for valves with nominal diameters below DN32mm. - Method 2: Open the gate, apply the test pressure, close it, open one end, and check for leaks. Repeat the process until the test is passed. Before the seal test, the packing and gasket must be inspected.
(3) **Ball Valve**: For strength testing, the ball should be half-open. - Floating Ball Valve: In a half-open position, introduce the medium from one side, close the other end, rotate the ball several times, and check the packing and gasket for leaks. Repeat the test from the other side. - Fixed Ball Valve: Rotate the ball before testing, apply pressure from one end, check the inlet sealing performance using a precision pressure gauge, and repeat from the other side. Then, fill the cavity under test pressure and inspect the packing and gasket. - Three-way ball valves require leak tests at multiple positions.
(4) **Plug Valve**: - Strength Test: Introduce the medium from one end, close the other passages, and rotate the plug to fully open positions. No leakage indicates success. - Seal Test: Keep the cavity pressure equal to the passage pressure, rotate the plug to the closed position, check from the opposite end, and repeat after rotating 180°. Apply non-acid lubricant before testing, and ensure no visible leaks within the time limit. Gas valves are tested at 1.25 times working pressure.
(5) **Butterfly Valve**: Strength test is similar to shut-off valves. For the seal test, introduce the medium from the flow end, keep the disc open, and check for leaks. Close the disc and check the other end. Flow-regulating butterfly valves may not require this test.
(6) **Diaphragm Valve**: Introduce the medium from either end, open the flap, close the other end, and apply pressure. Check for leaks in the body and cover. Reduce pressure to the sealing test level, close the flap, and check the other end for leaks.
(7) **Check Valve**: Lift check valves should have the disc axis perpendicular to the horizontal, while swing check valves should align the disc axis parallel to the horizontal. During the strength test, the medium is introduced from the inlet, and the outlet is closed. No leaks during the test are acceptable. For the seal test, the medium is introduced from the outlet, and the inlet is checked for leaks.
(8) **Safety Valve**: - Strength test: Use water, apply pressure from the inlet, and check for leaks. - Sealing and constant pressure test: Use steam, air, or water depending on the valve type. Nitrogen is often used for critical safety valves. The test pressure is the nominal pressure, and at least two tests are conducted. Leak detection can be done using paper or plastic plates sealed with butter. - Constant pressure and return pressure tests must be performed at least three times. Refer to GB/T 12242–1989 for detailed procedures.
(9) **Pressure Reducing Valve**: - Strength test: Conduct after assembly, with pressure applied for at least 3 minutes for sizes larger than DN150. - Seal test: Use the actual working medium, apply 1.1 times the nominal pressure for air or water, and the maximum allowable working pressure for steam. Ensure the pressure difference between inlet and outlet is at least 0.2 MPa. Test the valve’s responsiveness and check for leaks. Gas valves are tested at 1.25 times working pressure.
Valve testing is a crucial step in ensuring product quality and safety. Manufacturers must strictly follow industry standards and best practices to guarantee reliable performance and customer satisfaction.
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