Valves are essential components in piping systems, serving various functions such as controlling, regulating, and protecting the flow of media. They can be classified based on their function, pressure rating, temperature range, actuation method, size, structural features, and connection types. Understanding these classifications helps in selecting the right valve for specific applications.
**Function-Based Classification**
1. **Shut-off Valves**: These valves are used to open or close the flow of a medium in a pipeline. Examples include gate valves, globe valves, plug valves, ball valves, butterfly valves, and diaphragm valves.
2. **Check Valves**: Also known as non-return valves, they prevent backflow of the medium. The bottom valve of a water pump is an example of this type.
3. **Safety Valves**: Designed to protect systems from overpressure by releasing excess pressure when it exceeds safe limits.
4. **Regulating Valves**: These valves adjust parameters like pressure and flow. They include pressure-reducing valves, throttle valves, and control valves.
5. **Diverter Valves**: Used to distribute, separate, or mix media in a pipeline. This category includes distribution valves and traps.
6. **Exhaust Valves**: Essential in pipeline systems, especially in boilers, HVAC, and oil and gas pipelines. They remove trapped air, improving system efficiency and reducing energy consumption.
**Pressure-Based Classification**
- **Vacuum Valves**: Operate at pressures below atmospheric.
- **Low-Pressure Valves**: Nominal pressure (PN) ≤ 1.6 MPa.
- **Medium-Pressure Valves**: PN = 2.5, 4.0, 6.4 MPa.
- **High-Pressure Valves**: PN = 10–80 MPa.
- **Ultra-High-Pressure Valves**: PN ≥ 100 MPa.
**Temperature-Based Classification**
- **Ultra-Low-Temperature Valves**: For temperatures < -100°C.
- **Cryogenic Valves**: For temperatures between -100°C and -40°C.
- **Normal-Temperature Valves**: For temperatures between -40°C and 120°C.
- **High-Temperature Valves**: For temperatures > 450°C.
**Actuation Method Classification**
- **Automatic Valves**: Operate without external force, using the medium's energy. Examples: safety valves, check valves, and pressure regulators.
- **Power-Driven Valves**: Operated by electric, pneumatic, or hydraulic power. Includes electric, pneumatic, and hydraulic valves.
- **Manual Valves**: Operated manually using levers, handles, or gears. Suitable for smaller torque applications.
**Size-Based Classification**
- **Small-Diameter Valves**: DN ≤ 40 mm.
- **Medium-Diameter Valves**: DN = 50–300 mm.
- **Large-Diameter Valves**: DN = 350–1200 mm.
- **Extra Large-Diameter Valves**: DN ≥ 1400 mm.
**Structural Classification**
- **Gate Valves**: The closure moves vertically along the seat centerline.
- **Plug Valves**: The closure moves perpendicular to the seat.
- **Ball Valves**: The closure rotates around its axis.
- **Swing Check Valves**: The closure swings around an external pivot.
- **Butterfly Valves**: The disc rotates around a fixed shaft.
- **Spool Valves**: The closure slides perpendicular to the flow path.
**Connection Type Classification**
- **Threaded Valves**: Connected via internal or external threads.
- **Flanged Valves**: Connected using flanges.
- **Welded Valves**: Connected via welding.
- **Clamp-Connected Valves**: Fastened using clamps.
- **Ferrule-Connected Valves**: Joined with ferrules.
- **Socket-Weld Valves**: Connected by bolting directly to pipes.
**Material-Based Classification**
- **Metal Valves**: Made from materials like cast iron, carbon steel, stainless steel, etc.
- **Non-Metallic Valves**: Made from plastics, ceramics, or glass fiber.
- **Lined Valves**: Metal bodies with lined surfaces for corrosion resistance.
**Valve Model Standardization**
The valve model typically includes information such as type, drive method, connection type, structure, sealing material, nominal pressure, and body material. While China has a standard for valve numbering, manufacturers often adapt their own systems due to the increasing complexity of modern valve designs.
In summary, valves play a critical role in industrial and commercial systems. Proper selection and maintenance are essential to ensure safety, efficiency, and reliability. Whether it’s a simple shut-off valve or a complex safety device, understanding the classification and function of each type is key to effective system design and operation.
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