Valve pressure testing issues

It depends on what type of valve you are using; under normal circumstances, it doesn’t leak

For valves with forced sealing, their ability to maintain pressure at levels below the specified sealing pressure is greater, such as in the case of conventional gate valves and stop valves； For some components that rely on medium pressure for assistance, their sealing performance at low pressures actually decreases, such as check valves. It is relatively easy to make the medium water leak-free, so that it will not leak at all.

The hydraulic pressure test for valves seems to be at a factor of ×1.25; once the pressure is applied, it is possible to check whether there is any leakage at the various moving and stationary sealing points. Valves have a directionality aspect – pressure testing should be carried out in the direction in which the valve is supposed to be closed. Additionally, the valve should be fully opened to verify whether the sealing at the valve’s packing is adequate. Remember, do not blindly seal the packing just because a leak is detected. After tightening, it is essential to ensure that the valve operates smoothly; there should be no restriction in its movement or excessive tightness, as this can damage the valve.

1. Before installation, a visual quality inspection should be carried out: the valve body must be in good condition, the operating mechanism must function smoothly, the valve stem must not be skewed, deformed, or stuck, and all labels must be present； 2. Conduct shell pressure tests and sealing tests; valves with an upper sealing structure shall also undergo an upper sealing test, and those that fail these tests must not be used. 3. The shell pressure test and seal test shall be conducted using clean water as the medium. When testing stainless steel valves, the chloride ion content in water must not exceed 25 ppm. Once the test is passed, the water stains should be removed immediately. When there are special requirements, the test medium shall comply with the provisions of the design documents. 4. The test pressure for the housing shall be 1.5 times the maximum allowable operating pressure at 20°C, while the test pressure for the seal shall be 1.1 times the maximum allowable operating pressure at 20°C. When the valve nameplate indicates that a high-pressure sealing test is not suitable for the maximum operating pressure difference or the actuator supplied with the valve, the test pressure shall be 1.1 times the maximum operating pressure difference indicated on the valve nameplate. 5. The test pressure for the upper seal shall be 1.1 times the maximum allowable operating pressure at 20°C. During testing, the upper sealing surface should be closed, and the packing gland should be loosened. 6. The valve must remain under the test pressure for no less than 5 minutes. Unless otherwise specified, the temperature of the test medium should be between 5°C and 40°C; if it is below 5°C, measures should be taken to raise the temperature. 7. Gate valves with a nominal pressure of less than 1.0 MPa and a nominal size of 600 mm or more may be exempted from separate shell pressure testing and gate seal testing. The shell pressure test should be conducted at the system pressure testing stage, using the test pressure of the piping system. The gate seal test can be used to inspect the seal surface of the gate by methods such as color marking; the color marks on the joint surface should be continuous. 8. The jacket portion of the jacketed valve shall be pressure-tested at 1.5 times the design pressure. 9. Valves that pass the tests should have any water accumulated inside them drained promptly and dried out. Except for valves that require degreasing, rust preventive oil should be applied to the sealing surfaces and valve stem. The valves should be closed, the inlets and outlets should be sealed, and clear markings should be made. 10. After the valve test is successful, a “Valve Test Record” should be filled out. 11. The calibration of safety valves shall be carried out in accordance with the **current standard ‘Regulations on Safety Technical Supervision of Safety Valves’ TSG ZF001 and the provisions of the design documents, including setting of the adjustment pressure and conduct of seal tests; when there are special requirements, other performance tests shall also be performed. Records and lead seals should be kept for the safety valve calibration, and a calibration report should be issued.

There are two types of sealing that must be implemented for valves: high-pressure sealing and low-pressure sealing. The high-pressure threshold is 1.1 times the PN value, while the low-pressure threshold is 0.6 MPA. Some valves also require sealing tests. Generally, if a valve has no leaks under high-pressure conditions, it will also not leak within the range of 1.0–1.6 MPA. For certain types of valves, such as triple-eccentric butterfly valves, it is relatively easy to ensure no leaks at high pressures; however, achieving no leaks at low pressures is more difficult. We have encountered cases where valves with a PN16 rating passed the standard pressure tests with zero leaks under both high-pressure and low-pressure conditions, but when installed in actual pipelines under a pressure of only 2 kilograms, these valves started leaking

This is a bit abstract; it depends on what kind of valve it is – some valves simply must not leak at all.