Detailed Explanation of Various Industrial Valve Pressure Testing Methods
The pressure test of industrial valves is a crucial step to ensure their performance and safety. Due to the structural differences among various types of valves, specific pressure testing methods need to be adopted. Based on general principles and specific valve types, the following provides a complete pressure test operation guide:
I. General Pressure Testing Principles
1. Scope of Application
The new valves are usually only subjected to the sealing test, but the valve bodies/valve covers that have been repaired or have corrosion damage need to undergo the strength test.
The safety valve needs to undergo pressure setting, reseating pressure and other tests in accordance with the instructions and specifications.
2. Inspection Ratio
20% of the low-pressure valves will be randomly inspected. If any are found to be不合格， all of them will be re-inspected； for medium and high-pressure valves， 100% inspection is required.
3. Test medium
Common media include water, oil, air, steam, nitrogen, etc. Safety valves are selected based on the type of medium (for example, saturated steam for steam, air for gases).
4. Duration
The strength/sealing test usually lasts for 2 to 3 minutes. For important valves, the duration is extended to 5 minutes; for small-diameter valves, the time is shortened, and for large-diameter valves, it is prolonged.
II. Specific Valve Pressure Testing Methods
1. Ball valve
Strength test: In the semi-open state of the sphere, inject the medium from one end to the specified pressure, and check for leakage from the valve body/valve cover.
Sealing test:
Floating type: Rotate the ball in the semi-open position. When closed, check the packing and gaskets; repeat the test from the other end.
Fixed type: Inject the medium in the closed state, and use a pressure gauge (with an accuracy of 0.5-1 level and a range of 1.5 times the test pressure) for detection; check the internal cavity seal in the semi-open state.
Three-way ball valve: Sealing tests must be conducted at all positions.
2. Gate Valve
Strength test: The same as the stop valve.
Sealing test:
Intermediate pressure test: Open the gate plate to increase the pressure, then close it. Remove and inspect the seals on both sides; or inject the medium into the plug to test (not suitable for DN32mm or smaller).
Blind plate inspection method: After pressurization, close the gate plate, open the blind plate at one end to inspect the sealing surface, and repeat the test.
3. Check Valve
Test status: The axis of the lift valve disc is vertical, while the swing opening type channel/valve disc axis is approximately horizontal.
Strength test: Inject the medium from the inlet end to check for leakage in the valve body/valve cover.
Sealing test: Inject the medium from the outlet end, and inspect the sealing surface, packing and gasket at the inlet end.
4. Butterfly Valve
Strength test: The same as the stop valve.
Sealing test: Open the butterfly plate and inject the medium to check the packing and the sealing area; after closing, check the sealing of the butterfly plate.
Exception: The butterfly valve used for regulating flow can be exempted from the sealing test.
5. Globe Valve
Strength test: Inject the medium from one end, seal the remaining passages, rotate the plug to the fully open position to check for leakage.
Sealing test:
Direct-flow type: Keep the pressure inside the chamber equal to the pressure in the passage, rotate the plug to the closed position for inspection; repeat the 180° test.
Three-way / Four-way type: Introduce pressure from the right-angle end, and check the sealing at the other ends.
Allow the use of non-acidic thin lubricating oil. The test duration is 1 to 3 minutes. For the gas valve, an air sealing test at 1.25 times the working pressure is required.
6. Diaphragm Valve
Strength test: Inject the medium from either end, open the valve disc, and check for leakage from the valve body/valve cover.
Sealing test: After reducing the pressure, close the valve disc and check for any leakage at the other end.
7. Pressure Reducing Valve
Strength test: Conducted on individual units or after assembly. For the bellows, a 1.5 times the maximum pressure air test is required after welding.
Sealing test:
Air/Water: 1.1 times the nominal pressure.
Steam: The maximum pressure at the working temperature.
The pressure difference between the inlet and the outlet is ≥ 0.2 MPa. The adjusting screw enables the outlet pressure to change sensitively, without any stagnation or jamming.
Steam pressure reducing valve: The increase in outlet pressure within 2 minutes after the shut-off valve is closed must comply with the regulations, and the volume of the pipeline after the valve must meet the standards.
Water/Air Pressure Reducing Valve: Closes when the outlet pressure is zero and there is no leakage within 2 minutes.
8. Safety Valve
Strength test: Conducted with water. Pressure was introduced to the lower part of the valve body from the inlet end, and to the upper part from the outlet end.
Sealing test: Nominal pressure value, at least two times, no leakage within 5 minutes.
Leak detection method:
Butter paper method: The thin paper bulges to form a leak.
Water-filling method: The water is considered qualified if no bubbles are present.
Pressure holding/reseating test: At least 3 times, in accordance with the GB/T 12242 standard.
III. Key Considerations
1. Installation position: The valve should be placed in a direction that is convenient for inspection.
2. Welding of valves: When blind plate pressure testing is not feasible, conical or O-ring seals can be used for sealing.
3. Hydraulic test: Try to remove air to avoid errors.
4. Boosting pressure: Gradually increase the pressure to prevent damage to the equipment caused by sudden pressure increase.
5. Closing Force: Only one person with normal physical strength is allowed to close. When the handwheel is ≥ 320mm, two people are permitted to operate.
6. Install the sealing valve: Remove the packing for the sealing test. After the sealing is closed, check for any leakage (during the gas test, water is injected into the stuffing box for observation).
7. Record and Label: After the pressure test, record and label (✓ for qualified, × for unqualified), stack separately, and cover for protection.
IV. Special Notes
Throttle valve: No sealing test for the closing element is required, but strength test and packing/ gasket sealing test must be conducted.
Selection of test medium: Based on the type of valve and the properties of the medium (such as saturated steam for steam safety valves).
Pressure holding time: The shell strength test is held at pressure for 5 minutes. The upper seal test is held at pressure according to the DN size classification (15s - 120s).
By following the above methods, the standardization and effectiveness of pressure testing for various industrial valves can be ensured, thereby safeguarding the safe operation of industrial equipment.
