Standards for judging the quality of gate valves
To judge the quality of gate valves, a comprehensive evaluation is required from multiple dimensions, including performance parameters, material quality, manufacturing process, and adaptability to actual working conditions. The following are specific evaluation criteria for reference during procurement, acceptance or maintenance:
I. Core performance indicators
1. Sealing performance
Internal leakage test: Perform air pressure or water pressure test according to standards (such as API 598, ISO 5208), and the leakage after the valve is fully closed must meet the grade requirements (such as zero leakage for Class VI).
External leakage inspection: There is no leakage at the valve stem packing (such as graphite packing) and the valve body connection.
2. Strength performance
Pressure resistance: The valve body must withstand a static pressure test of 1.5 times the nominal pressure (PN) without deformation or rupture (refer to ASME B16.34).
3. Operational performance
Opening and closing torque: Manual valves should rotate flexibly, and electric/pneumatic valves must match the actuator thrust (excessive torque may indicate internal jamming).
Travel time: For automatic valves, the opening and closing time should meet the design requirements (such as emergency shut-off valves are usually required to be ≤5 seconds).
2. Materials and manufacturing processes
1. Valve body and key component materials
Valve body/valve cover: Select according to the medium (such as WCB carbon steel for ordinary water and oil, CF8M stainless steel for corrosive media).
Gate and valve seat:
Hard seal: Stellite or tungsten carbide surfacing, high temperature wear resistance.
Soft seal: EPDM, PTFE, suitable for low temperature or clean media.
2. Processing accuracy
Sealing surface finish: Ra≤0.8μm (mirror effect), to ensure sealing fit.
Gate and guide rail fit: gap ≤0.1mm to prevent jamming or offset.
3. Surface treatment
Anti-corrosion coating: such as nickel plating, spraying epoxy resin, used in marine or chemical environments.
3. Reasonable structure and design
1. Valve stem design
Lifting type vs. rotating type: The lifting stem is easier to observe the opening, but requires a larger installation space.
Anti-blowout structure: The bottom of the valve stem should have a T-shaped head or similar design to prevent the valve stem from falling off under high-pressure media.
2. Flow resistance characteristics
Full-bore design (such as API 6D gate valve) can reduce pressure loss and is suitable for conveying viscous media or slurries.
3. Maintenance convenience
Modular design: The valve seat can be replaced online (such as API 6D gate valve) to reduce downtime.
4. Working condition adaptability
1. Temperature and pressure range
High-temperature gate valves (＞200℃) need to consider thermal expansion compensation design (such as elastic gate valve).
Low-temperature valves (＜-29℃) use austenitic stainless steel to avoid cold brittleness.
2. Medium compatibility
Medium containing particles: Use knife gate valve (Knife Gate Valve), and the gate valve has a self-cleaning function.
Corrosive media: Valve trims require Hastelloy or fluorine lining (such as PTFE lining).
V. Brand and certification
1. Industry certification
API 600 (oil and gas gate valve), CE/PED (EU Pressure Equipment Directive), ISO 9001 quality management system.
2. Manufacturer qualifications
Historical cases (such as nuclear power and petrochemical project experience), third-party test reports (SGS, BV).
Common problem warning
Low price trap: Inferior gate valves may use refurbished castings or substandard sealing materials.
False seal: The new valve passes the test, but leaks due to thermal deformation after operation (high temperature performance needs to be verified).
Comprehensive evaluation of the above standards can effectively screen out high-quality gate valves.