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Valve Maintenance (NZ) 2017 Ltd (VMNZ) are IANZ accredited to carry out hydrostatic testing of all types of industrial valves up to a maximum of 700 barG in accordance with standard API 527.

In a hydrostatic test, the valve body is filled with testing fluid and the pressure is applied for a specified length of time. The valve is then inspected for any leakage. The testing fluid can be water, water with a corrosion inhibitor, or another liquid whose viscosity is not greater than that of water. The testing pressure depends on what material the valve is made of: steel, nickel-base alloy, cast iron, and so on. The test duration depends on the nominal valve size and valve class.

Three conditions can cause a valve to be rejected:

1. There is visible leakage in the valve body assembly.
2. There is leakage through static seals and gasketed joints (unless allowed by design).
3. The hydrostatic test causes any distortion that impairs the valve operation.