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Valves can be classified in various ways based on their functions, structures, driving mechanisms, and material properties. This classification follows established international and national standards to ensure consistency and clarity.
**1. Classification by Function**
Valves serve different purposes depending on their design and application. The main categories include:
- **Shut-off Valves**: These are used to open or close the flow of a medium in a pipeline. Examples include gate valves, globe valves, ball valves, butterfly valves, diaphragm valves, and plug valves.
- **Check Valves**: Prevent backflow of media in a pipeline. Common examples include check valves and bottom valves.
- **Control Valves**: Used to regulate the pressure, flow, or temperature of the medium. Examples include pressure-reducing valves, throttling valves, and regulating valves.
- **Safety Valves**: Designed to protect equipment and pipelines from overpressure by releasing excess media when a set limit is reached. Examples include safety valves and emergency shut-off valves.
- **Special Purpose Valves**: Include traps, vent valves, and drain valves, each serving specific operational needs.
**2. Classification by Actuation Method**
Valves can also be categorized based on how they are operated:
- **Automatic Valves**: Operate without external force, relying on the system's own pressure or other inherent forces. Examples include safety valves, pressure relief valves, and steam traps.
- **Power-Driven Valves**: Require an external power source such as electricity, air, or hydraulic pressure. These include electric valves, pneumatic valves, and hydraulic valves. Some may combine multiple drive types, like gas-electric valves.
- **Manual Valves**: Operated manually using handwheels, levers, or gears. For high-torque applications, gearboxes or worm drives may be used. Long-distance operation can also be achieved with transmission shafts and universal joints.
**3. Classification by Nominal Pressure**
Pressure ratings determine the suitability of a valve for different systems:
- **Vacuum Valves**: Operate under pressures below atmospheric.
- **Low-Pressure Valves**: PN ≤ 1.6 MPa.
- **Medium-Pressure Valves**: PN = 2.5–6.4 MPa.
- **High-Pressure Valves**: PN = 10–80 MPa.
- **Ultra-High-Pressure Valves**: PN ≥ 100 MPa.
**4. Classification by Operating Temperature**
Temperature conditions influence material selection and design:
- **Normal Temperature Valves**: Operating temperatures between 40°C and 120°C.
- **Medium-Temperature Valves**: Temperatures between 120°C and 450°C.
- **High-Temperature Valves**: Temperatures above 450°C.
- **Cryogenic Valves**: Operate at temperatures between -100°C and 40°C.
- **Ultra-Low-Temperature Valves**: Operate at temperatures below -100°C.
**5. Classification by Nominal Diameter**
Valve size is determined by the nominal diameter (DN):
- **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.
**6. Classification by Structure**
The internal mechanism determines the type of motion involved:
- **Gate Valves**: The closing element moves linearly along the centerline of the seat.
- **Plug Valves**: The closing element rotates around its axis.
- **Butterfly Valves**: The disc rotates around a fixed axis within the valve body.
- **Sliding Valves**: The closing element slides perpendicular to the flow path.
- **Ball Valves**: The closing element is a sphere that rotates to control flow.
**7. Classification by Connection Type**
Valves can be connected to piping in several ways:
- **Threaded Valves**: Connected via internal or external threads.
- **Flanged Valves**: Attached using flanges.
- **Welded Valves**: Joined through welding.
- **Clamp-Type Valves**: Secured using clamps.
- **Sleeve-Type Valves**: Fastened using bolts and sleeves.
**8. Classification by Material**
The material of the valve body affects its durability and compatibility with different media:
- **Metallic Valves**: Made from materials like cast iron, carbon steel, stainless steel, copper alloys, aluminum alloys, titanium, and Monel.
- **Non-Metallic Valves**: Constructed from plastics, ceramics, glass, or enamel.
- **Lined Valves**: Metal bodies with internal linings such as rubber or plastic to resist corrosion or wear.
This comprehensive classification helps engineers and technicians select the most suitable valve for a given application, ensuring safe, efficient, and reliable operation in a wide range of industrial environments.