Valves Selection
To select a valve, follow these steps while considering the service conditions, valve functions, and cost :
- Determine the Valve Function: Decide if the valve will primarily be used for on/off control, throttling, preventing backflow, or specialty purposes such as pressure relief . Different valve types are better suited for specific functions .
- Identify Service Characteristics:
- Fluid Type: Determine if the fluid is a liquid, gas, steam, slurry, or solid .
- Fluid Properties: Identify if the fluid is clean, dirty, abrasive, corrosive, viscous, or hazardous .
- Pressure and Temperature: Determine the operating pressure and temperature ranges .
- Consider Valve Characteristics: Evaluate application and structural characteristics to ensure proper installation, repair, and maintenance .
- Assess Operation and Maintenance Requirements:
- Fire Resistance: Determine if fire-safe features are needed .
- Operability: Consider the required speed of operation (e.g., quarter-turn, multi-turn) and actuation method (manual, electric, pneumatic, hydraulic) .
- Leak Tightness: Determine acceptable leakage rates (internal and external) .
- Maintainability: Consider ease of access for maintenance and replacement .
- Evaluate Valve Types:
- Gate Valves: Suitable for on/off service with minimal flow restriction .
- Globe Valves: Used for throttling and on/off service, but with higher flow restriction .
- Ball Valves: Provide quarter-turn on/off operation with low-pressure drop .
- Butterfly Valves: Compact and lightweight, suitable for on/off and throttling of large flows .
- Plug Valves: Offer quarter-turn on/off operation, often used for diverting flow .
- Diaphragm Valves: Suitable for corrosive or contaminated fluids .
- Check Valves: Prevent backflow in a piping system .
- Consider the Cost: Evaluate not only the initial cost of the valve but also the installation, maintenance, and lifecycle costs .
- Check the valve size: Proper valve sizing is crucial for optimal performance. Use valve flow coefficient (Cv) calculations and consult valve manufacturers’ data to determine the correct size .