1. Valve Characteristics
Functional Characteristics: Define the valve's primary performance and application scope, including:
Valve type: Isolation valves (e.g., gate, globe), control valves (e.g., butterfly, ball), safety valves, etc.
Materials: Valve body, bonnet, stem, disc, and sealing surfaces (e.g., cast iron, carbon steel, stainless steel).
Actuation method: Manual, electric, pneumatic, hydraulic, etc.
Structural Characteristics: Determine installation, maintenance, and design features:
Dimensions: Structural length, height, connection type (flanged, threaded, welded).
Sealing design: Embedded rings, welded overlays, or integral body seals.
Stem type: Rising stem (linear motion) or non-rising stem (rotary motion).
2. Valve Selection Steps
Define the valve's purpose and operating conditions: Media type, pressure, temperature, and flow requirements.
Determine pipeline specifications: Nominal diameter and connection method (flange, thread, weld).
Choose actuation method: Manual, electric, pneumatic, or hydraulic.
Select materials: Based on media corrosivity, temperature, and pressure (e.g., ductile iron for water, stainless steel for chemicals).
Identify valve category: Isolation, regulation, or safety.
Specify valve type: Gate, globe, ball, butterfly, etc.
Calculate key parameters: For control valves, determine allowable pressure drop, flow capacity, and seat diameter.
Verify dimensions: Structural length, flange size, bolt hole patterns, and overall footprint.
Consult technical resources: Valve catalogs, manufacturer datasheets, and industry standards.
3. Selection Criteria
Application requirements: Purpose (isolation, throttling, safety), operating conditions, and control method.
Media properties: Pressure, temperature, corrosivity, viscosity, presence of solids, toxicity, or flammability.
Performance needs: Flow resistance, sealing integrity, leakage class, and actuation speed.
Installation constraints: Nominal size, connection type, space limitations, and weight.
Additional factors: Reliability, lifespan, and explosion-proof certifications for hazardous environments.
4. Valve Selection Principles
For Isolation/Shutoff:
Straight-through valves (e.g., gate, ball) with low flow resistance are preferred.
Avoid downward-closing valves (e.g., globe valves) unless high flow resistance is acceptable.
For Flow Control:
Globe valves are ideal due to proportional flow regulation via stem travel.
Rotary valves (ball, butterfly) and flexible-body valves (pinch, diaphragm) are limited to small sizes.
Gate valves are unsuitable for throttling due to poor flow control except near full closure.
For Flow Diversion:
Multi-port valves (e.g., 3-way ball valves, plug valves) are optimal.
Combinations of standard valves can also achieve diversion in specific cases.
For Slurry or Particulate Media:
Valves with self-cleaning seals (e.g., ball, plug valves) prevent particle buildup.
Avoid valves with vertical disc movement unless seals tolerate embedded particles.
Conclusion:
Valves are the ultimate control points in pipelines, critical for safety, efficiency, and reliability across industries like oil, gas, and chemicals. By systematically evaluating functional needs, media properties, and operational demands, engineers can select valves that ensure optimal performance and longevity.