Principles and Precautions for Valve Pressure Testing

(1) Generally, valves are not subjected to strength tests; however, valve bodies and bonnets—or valve bodies and bonnets that have been repaired or suffered corrosion damage—must undergo such tests. For safety valves, the set pressure, reseat pressure, and other relevant tests must comply with the manufacturer’s instructions and applicable regulations.
(2) Valve installations must undergo strength and sealing tests. For low-pressure valves, a random 20% sample should be tested; if any fail, 100% inspection is required. Medium- and high-pressure valves, however, must undergo 100% inspection.
(3) During testing, the valve should be installed in a position that allows for easy inspection.
(4) For valves with welded connections, if blind flange testing is not feasible, cone seals or O-ring seals can be used for pressure testing instead.
(5) During the hydraulic test, ensure that as much air as possible is expelled from the valve.
(6) During the test, the pressure must be increased gradually; rapid or sudden pressure surges are not permitted.
(7) The duration of pressure and leak-testing is typically 2 to 3 minutes; however, critical and special valves should be tested for 5 minutes. For valves with smaller diameters, the testing time can be slightly shorter, while larger-diameter valves may require longer testing periods. If any doubts arise during the test, the duration can be extended as needed. During the pressure test, neither sweating nor leakage should occur on the valve body or bonnet. Generally, standard valves undergo a single leak test, whereas critical valves such as safety valves and high-pressure valves must be tested twice. During the test, minor leakage is permissible for low-pressure, large-diameter, non-critical valves—as well as for valves explicitly permitted to have slight leaks according to specific regulations. Given the varying requirements for general-purpose valves, power plant valves, marine valves, and other types of valves, leakage criteria should strictly adhere to relevant industry standards.
(8) The throttling valve does not require a sealing test as a closing member, but it should undergo a strength test as well as sealing tests at the packing and gasket areas.
(9) During the pressure test, the closing force of valves must be applied using only one person’s normal physical strength; no leverage tools—or any other aids except torque wrenches—may be used to increase the force. However, when the handwheel diameter is 320 mm or larger, two people are permitted to close the valve together.
(10) Valves equipped with a top seal should have their packing removed for a sealing test. After the top seal is closed, check for any leaks. When conducting the test with gas, fill the packing chamber with water to perform the inspection. During the packing-seal integrity test, ensure that the top seal is not fully engaged in its sealed position.
(11) For any valve equipped with a driving mechanism, the sealing performance must be tested by closing the valve using the drive mechanism itself. Additionally, for valves operated manually, a sealing test must also be conducted while actively closing the valve with manual operation.
(12) After the main valve undergoes strength and sealing tests, the bypass valve installed on the main valve should also open simultaneously when the main valve’s closure member is actuated.
(13) During the strength test of cast iron valves, lightly tap the valve body and bonnet with a copper hammer to check for any leaks.
(14) When valves are being tested, oiling the sealing surfaces is permitted only for globe valves as specified; for all other types of valves, oiling the sealing surfaces during testing is not allowed.
(15) During valve pressure testing, the clamping force applied by the blind flange to the valve should not be excessive, as this could cause deformation of the valve and compromise the test results. (For example, if cast iron valves are pressed too tightly, they may even crack or break.)
(16) After the valve pressure test is completed, any accumulated water inside the valve should be promptly drained and thoroughly wiped clean. Additionally, a detailed test record must be kept.