Valves can be considered pressure vessels; therefore, they must withstand the pressure of the contained medium without leaking. Consequently, raw castings or forgings for components such as valve bodies and bonnets must be free from defects that compromise structural integrity, such as cracks, porosity, or slag inclusions. In addition to rigorously inspecting the external and internal quality of these raw components, manufacturers must conduct individual strength tests to ensure the valve's operational performance.
Globe valves and control valves (with the exception of throttle valves) require a certain level of shut-off tightness; they must be sealed individually before leaving the factory, and a backseat tightness test must be performed on the sealed valves.
Tests are typically conducted at room temperature and nominal pressure, though the pressure applied is often 1.1 times the nominal rating.
When water is used as the test medium, valves are prone to rusting. Generally, water quality must be controlled according to technical specifications, and any residual water must be dried off after testing.
Gate valves and ball valves require bidirectional sealing tests because they possess two sets of sealing surfaces. During the test, the valve is first opened, one end of the flow passage is blocked, and pressure is introduced from the opposite end. Once the pressure reaches the specified value, the valve is closed, and the pressure at the blocked end is gradually released for inspection. The procedure is then repeated from the other end. An alternative testing method for gate valves involves maintaining the test pressure within the valve body cavity and checking the double-sealing integrity from both ends of the flow passage.
When testing check valves, pressure is introduced from the outlet end, and the inlet end is inspected.
During sealing tests, the closing torque for the valve must be determined based on its nominal pressure and nominal diameter. Manual valves are generally intended to be closed using normal physical force, without the aid of auxiliary tools; however, for handwheels with a diameter of 320 mm, two-person operation is permitted. Valves equipped with actuators should be tested using the actuator itself. If technical specifications mandate a specific closing torque, a torque wrench should be used to measure it. Sealing tests should be performed after the valve has been assembled and has passed the strength test, as the procedure verifies not only the shut-off tightness but also the integrity of the bonnet packing and flange gaskets.
The backseat tightness test is usually conducted in conjunction with the strength test. During the test, the valve stem must be raised to the appropriate position to ensure tight contact between the stem and the bonnet sealing surface. The sealing integrity should be checked after loosening the packing gland.
For valves handling gaseous media, or those requiring a low-pressure gas seal test as specified in drawings and technical specifications, testing must be conducted in accordance with the relevant standards. The test medium shall be nitrogen or clean, dry air, and the test pressure shall be 0.6 MPa.
Tianjin Pulos valves are primarily used in industrial processes to control the flow of various fluids, such as water, oil, and chemical liquids. Key operating parameters include temperature, pressure, and flow rate. Common control valves used in industrial plants include pressure-reducing valves, pneumatic thermostatic valves, solenoid valve-based thermostatic systems, proportional control valve systems, and temperature control valves. When selecting automatic valves, factors such as the type of thermal equipment, required precision, and valve quality should be considered. Additionally, aspects such as pressure drop, flow characteristics, structural design, failure rate, manufacturer reputation, and after-sales service should be evaluated to ensure a solution that is both economical and practical.
