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The **People's Republic of China Power Industry Standard DL/T 531-94** outlines the technical specifications for high-temperature and high-pressure stop valves and gate valves used in power stations. This standard was approved on March 18, 1994, and came into effect on October 1, 1994. It covers the classification, design, and quality requirements for these critical components.
This standard applies to valves with nominal pressures (pN) of 20, 25, and 32 MPa, operating at temperatures not exceeding 425°C. It also includes valves with working pressures of 10, 14, and 17 MPa, operating at temperatures of 510°C, 540°C, and 570°C, respectively. The working medium is typically water or steam, and the valves are designed as shut-off and gate valves.
### References
The standard references several key industry standards, including:
- JB 2765: Valve Terminology
- JB 4018: Preparation Method for Power Station Valves
- ZBJ 98015: Technical Conditions for Pressure-Bearing Steel Castings
- GB 12231: Appearance Quality Requirements for Valve Castings
- GB 1176: Technical Conditions for Casting Copper Alloys
- GB 699: Technical Conditions for High-Quality Carbon Structural Steel
- GB 3077: Technical Conditions for Alloy Structural Steel
- GB 979: Classification and Technical Conditions for Carbon Steel Castings
- GB 4981: Pressure Test for Industrial Valves
- GB 6414: Dimensional Tolerances for Castings
- GB 1804: Tolerances and Deviations for Non-Dimensional Dimensions
- GB 3595: Manufacturing Technology for Power Station Valves
- GB 5677: Radiographic Testing and Film Classification Methods for Castings
- GB 7233: Ultrasonic Flaw Detection and Quality Rating for Steel Castings
- GB 9443: Penetrant Testing and Quality Rating for Steel Castings
- GB 9444: Magnetic Particle Inspection and Quality Rating for Castings
- SDB DZ Series: Electric Actuators for Valves
- SDZ: General Technical Conditions for Packaging
### Definitions
- **Shut-off Valve**: A valve where the closing element (disc) moves along the axis of the seat for opening and closing.
- **Gate Valve**: A valve where the gate moves along the sealing surface of the seat for opening and closing.
- **Manual Shut-off Valve/Gate Valve**: Operated manually via a handwheel or gear.
- **Electric Shut-off Valve/Gate Valve**: Operated by an electric actuator.
### Design and Assembly
- The stuffing box depth should be twice the stem diameter. For stems larger than 64 mm, the minimum depth is 110 mm.
- Pressure self-sealing valves should use flexible graphite spiral wound gaskets without joints.
- Handwheels must be marked and turned clockwise for operation.
- Electric actuators must comply with the "DZ series valve electric device" requirements.
- All parts must be inspected and labeled before assembly.
- Critical components must be rechecked for size and surface finish.
- Surfaces and friction areas must not affect performance.
- No burrs, corrosion, or machining defects are allowed on parts before assembly.
- Fasteners must be tightened and coated with heat-resistant grease.
- Manual valves must operate smoothly without sticking.
- Electric valves must have travel switches aligned with fully open and closed positions.
- After assembly, the gate center should be higher than the valve seat center, with specific values depending on single or double gate design.
- Rust removal and painting must occur after the hydrostatic test, ensuring no water residue remains.
- Non-machined surfaces should be primed with red lead before painting.
- All painted surfaces must be clean and free from grease.
### Testing
- Material testing must follow the provisions of Section 5.2.2.
- Hydraulic pressure tests must include shell strength and seal tests, as well as reverse seal tests.
- Type testing is required under certain conditions, such as new product development, major design changes, or requests from quality supervision agencies.
- Type tests include material analysis, hydrostatic testing, stress analysis, static pressure life testing, and resistance characteristic testing.
### Marking, Packaging, and Storage
- Each valve must be clearly marked with manufacturer name, product model, main parameters, production date, and quality grade.
- The valve body must be cast with material code, nominal pressure, nominal diameter, and flow direction.
- During packaging, transportation, and storage, valves must be closed and protected from dust and contamination.
- Valves must be securely packed to avoid damage during transport.
- Each package must include the product certificate, test reports, assembly drawings, and packing list.
- Valves should be stored in dry, covered areas to prevent exposure to moisture and damage.
This comprehensive standard ensures that high-temperature and high-pressure valves meet strict safety and performance criteria, making them suitable for use in power generation facilities across China.