Valves are essential components in various industrial and residential systems, serving different purposes based on their design, function, and application. Understanding the classification of valves helps in selecting the appropriate type for specific requirements.
**1. Classification by Purpose and Function**
- **Shut-off Valves**: These valves are primarily used to cut off or connect the flow of media. Common types include gate valves, globe valves, diaphragm valves, ball valves, plug valves, butterfly valves, needle valves, and others. They are ideal for applications where a full on/off control is needed.
- **Regulating Valves**: Designed to control the flow, pressure, or temperature of the medium, these valves include control valves, throttling valves, and pressure-reducing valves. They are crucial in maintaining system stability and efficiency.
- **Check Valves**: Prevent backflow of the medium, ensuring it flows only in one direction. Types include swing check valves and lift check valves, which operate automatically based on fluid pressure.
- **Diverter Valves**: Used to separate, distribute, or mix media. Examples include distribution valves, traps, and other specialized structures.
- **Safety Valves**: Protect equipment from overpressure by releasing excess pressure when necessary. These are vital in high-risk environments to prevent catastrophic failures.
**2. Classification by Main Parameters**
- **Pressure Classification**:
- **Vacuum Valves**: Operate under pressures below atmospheric.
- **Low Pressure Valves**: Nominal pressure (PN) less than 1.6 MPa.
- **Medium Pressure Valves**: PN ranges from 2.5 to 6.4 MPa.
- **High Pressure Valves**: PN ranges from 10 to 80 MPa.
- **Ultra-High Pressure (UHP) Valves**: PN greater than 100 MPa.
- **Temperature Classification**:
- **High-Temperature Valves**: T > 450°C.
- **Medium-Temperature Valves**: 120°C < T < 450°C.
- **Room-Temperature Valves**: -40°C < T < 120°C.
- **Cryogenic Valves**: -100°C < T < -40°C.
- **Super-Cryogenic Valves**: T < -100°C.
- **Material Classification**:
- **Non-Metallic Valves**: Such as ceramic, glass fiber, and plastic valves.
- **Metallic Valves**: Including copper alloys, aluminum alloys, carbon steel, stainless steel, and more.
- **Lined Metal Valves**: Featuring linings such as lead, plastic, or enamel for enhanced corrosion resistance.
**3. General Taxonomy**
This classification is based on the valve’s principle, function, and structure. Common types include gate valves, globe valves, throttle valves, ball valves, butterfly valves, check valves, safety valves, and others. It is widely used internationally and domestically.
**How to Choose the Right Valve**
Selecting the correct valve involves understanding the application, media properties, and system requirements. Key considerations include:
- Using ball valves or gate valves for full open/close operations.
- Avoiding partial openings to reduce wear and potential damage.
- Ensuring proper sealing to prevent leaks, especially with hazardous media.
- Considering electric, pneumatic, or hydraulic actuators for automated control.
- Choosing the right material based on temperature, pressure, and chemical compatibility.
**Key Valve Types and Their Features**
- **Butterfly Valves**: Known for their compact design, quick operation, and low pressure drop. Ideal for large diameter pipelines.
- **Ball Valves**: Provide tight shut-off with minimal torque and excellent flow control. Suitable for both general and harsh environments.
- **Gate Valves**: Offer reliable shut-off but are not suitable for flow regulation due to high resistance.
- **Globe Valves**: Excellent for flow control and throttling, with a linear motion stem.
- **Check Valves**: Automatically prevent reverse flow, ensuring unidirectional media movement.
- **Safety Valves**: Critical for protecting systems from overpressure, often used in steam and gas applications.
**Technical Performance of Valves**
- **Strength Performance**: The ability to withstand internal pressure without failure.
- **Sealing Performance**: Ensures no leakage, crucial for safety and environmental protection.
- **Flow Resistance**: Minimizing pressure loss is key for energy efficiency.
- **Action Performance**: Refers to the sensitivity and reliability of the valve during operation.
- **Opening/Closing Force and Torque**: Influences ease of operation and maintenance.
- **Opening/Closing Speed**: Important for emergency situations or systems requiring rapid response.
**Valve Identification and Painting**
Valves are often painted according to their body material and sealing surface to aid in identification. For example:
- **Gray Iron**: Black paint.
- **Stainless Steel**: No paint allowed.
- **Copper Alloys**: Not painted.
Paint colors on handwheels and handles also indicate sealing materials, aiding in maintenance and selection.
**General Principles for Water Supply Systems**
In water supply systems, valve selection follows specific guidelines:
- Small-diameter pipes (<50 mm) typically use globe valves.
- Larger pipes (>50 mm) may use gate or butterfly valves.
- Flow regulation requires control valves.
- Install valves at critical points like pump outlets, water meters, and distribution lines to ensure system integrity and safety.
By understanding these classifications, features, and selection criteria, engineers and technicians can make informed decisions to optimize system performance, safety, and longevity.
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