Detailed explanation of pressure testing methods for various industrial valves

The pressure testing of industrial valves is a crucial step in ensuring their performance and safety. Different types of valves require targeted pressure testing methods due to structural differences. The following provides a complete pressure testing operation guide based on general principles and specific valve types:

 General principle of pressure testing

1. Scope of application

New valves usually only undergo sealing tests, but repaired or corroded valve bodies/covers require strength tests.

The safety valve needs to undergo constant pressure and reseating pressure tests according to the instructions and specifications.

2. Inspection ratio

20% of low-pressure valves will be randomly inspected, and if they fail, a full inspection will be conducted; Medium and high pressure valves require 100% inspection.

3. Test medium

Common media include water, oil, air, steam, nitrogen, etc. The safety valve is selected according to the type of medium (such as saturated steam for steam and air for gas).

4. Duration

The strength/sealing test is generally 2-3 minutes, and for important valves, it is extended to 5 minutes; The time for small caliber valves is shortened, while the time for large caliber valves is extended.

 Specific valve pressure testing method

1. Ball valve

① Strength test: The sphere is in a semi open state, and the medium is injected from one end to the specified pressure to check for leakage in the valve body/valve cover.

② Sealing test:

Floating type: Rotate the sphere in a semi open state, and check the packing and gasket when closing; Repeat the experiment from the other end.

Fixed type: Inject the medium in the closed state and use a pressure gauge (accuracy level 0.5-1, range 1.5 times the test pressure) to detect it; Check the sealing of the inner cavity in a semi open state.

Three way ball valve: A sealing test must be conducted at all positions.

2. Gate valve

① Strength test: Same as globe valve.

② Sealing test:

• Intermediate pressure test: Open the gate to increase pressure, then close it and take it out to check the seals on both sides; Or inject the medium into the plug for detection (not suitable for use below DN32mm).

Blind plate inspection method: After increasing the pressure, close the gate plate, open one end of the blind plate to inspect the sealing surface, and repeat the test.

3. Check valve

① Test state: The axis of the lifting valve disc is vertical, and the axis of the swing channel/valve disc is approximately horizontal.

② Strength test: Inject medium from the inlet end and check for leakage in the valve body/valve cover.

③ Sealing test: Inject medium from the outlet end and check the sealing surface, packing, and gasket at the inlet end.

4. Butterfly valve

① Strength test: Same as globe valve.

② Sealing test: Open the butterfly plate to inject the medium, check the packing and sealing parts; Check the butterfly plate seal after closing.

③ Exception: Butterfly valves used for regulating flow are exempt from sealing tests.

5. Plug valve

① Strength test: Inject medium from one end, seal the remaining passages, and rotate the plug to the fully open position to check for leakage.

② Sealing test:

Direct type: Maintain equal pressure between the cavity and the passage, rotate the plug to the closed position for inspection; Repeat the 180 ° test.

Three way/four-way: Introduce pressure from the right angle end and check the sealing at the other end.

Allow the application of non acidic lubricating oil, with a test time of 1-3 minutes; Gas plug valves require an air seal test at 1.25 times the working pressure.

6. Diaphragm valve

① Strength test: Inject medium from either end, open the valve disc, and check for leakage in the valve body/cover.

② Sealing test: After reducing pressure, close the valve disc and check for leakage at the other end.

7. Pressure reducing valve

① Strength test: Single piece or assembled test, and 1.5 times the maximum pressure air test is required after welding the corrugated pipe.

② Sealing test:

Air/water: 1.1 times nominal pressure.

• Steam: maximum pressure at operating temperature.

The pressure difference between the inlet and outlet is ≥ 0.2MPa. Adjust the screw to make the outlet pressure change sensitively without stagnation or blockage.

• Steam pressure reducing valve: Within 2 minutes after closing the shut-off valve, the outlet pressure increase must comply with regulations, and the pipeline volume behind the valve must meet the standard.

Water/air pressure reducing valve: Close when the outlet pressure is zero and there is no leakage within 2 minutes.

8. Safety valve

① Strength test: Water test, with pressure introduced from the inlet end at the lower part of the valve body and from the outlet end at the upper part.

② Sealing test: nominal pressure value, no less than twice, no leakage within 5 minutes.

③ Leak detection method:

• Butter thin paper method: When the thin paper bulges, it becomes a leak.

Irrigation method: If there is no bubbling in the water, it is qualified.

• Constant pressure/reseating pressure test: no less than 3 times, in accordance with GB/T 12242 standard.

 Key precautions

1. Installation position: The valve should be placed in a direction that is easy to inspect.

2. Welded valves: When blind plate pressure testing is not feasible, conical or O-ring sealing should be used.

3. Hydraulic test: Try to eliminate air as much as possible to avoid errors.

4. Boosting: Gradually increase the pressure to avoid equipment damage caused by sudden boosting.

5. Closing force: Only one person is allowed to close with normal physical strength, and two people are allowed to operate when the handwheel is ≥ 320mm.

6. Upper sealing valve: Remove the packing for sealing test, check for leakage after closing the upper seal (observe by filling the packing box with water during gas test).

7. Record and label: After pressure testing, record and label (√ qualified, × unqualified), stack separately, and cover for protection.

Special Instructions

Throttle valve: No sealing test is required for the closing component, but strength test and packing/gasket sealing test are required.

• Selection of test medium: Based on valve type and medium characteristics (such as saturated steam for steam safety valves).

• Holding time: Hold the shell strength test for 5 minutes, and hold the upper seal test according to DN size grading (15s-120s).

Following the above methods can ensure the standardization and effectiveness of pressure testing for various industrial valves, ensuring the safe operation of industrial equipment.