Four Principles for Valve Selection: Reliability, Suitability, Convenience, And Economy

I. Define the Application Working Conditions

• Medium Characteristics: Types of fluids (liquid, gas, steam, corrosive medium, containing particles, etc.), temperature, pressure, viscosity, toxicity, etc.

• Example: For corrosive media (such as acids and alkalis), corrosion - resistant materials (such as stainless - steel, plastic, ceramic valves) need to be selected; for high - temperature steam, cast - steel or alloy - steel valves are required.

• Operating Conditions: Working pressure (maximum/minimum), temperature range, flow requirements, opening and closing frequency, etc.

• Example: High - pressure systems (such as the main steam pipeline of power plants) need to select high - strength forged - steel valves.

  
  

II. Select the Valve Type

Select the appropriate valve type according to functional requirements:

• Globe Valve: Precise flow regulation, but with relatively large pressure loss.

• Gate Valve: Fully open/fully closed, low flow resistance, suitable for large - diameter pipelines.

• Ball Valve: Quick opening and closing, good sealing performance, suitable for clean media.

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• Butterfly Valve: Compact structure, suitable for low - pressure and large - flow regulation.

• Check Valve: Prevents the back - flow of the medium.

• Safety Valve: Over - pressure protection.

• Control Valve: Flow/pressure regulation in automated control systems.

  
  

III. Flow and Pressure Loss

• Flow Requirements: The valve nominal diameter (DN) needs to be matched with the pipeline to ensure that the flow meets the process requirements.

• Pressure Loss: The flow resistance of different valve structures varies significantly (for example, ball valves have low flow resistance, while globe valves have high flow resistance), and selection should be based on the system energy consumption requirements.

  
  

IV. Sealing Performance

• Leakage Rating: Select the sealing rating according to the danger of the medium (such as API 598, ISO 5208 standards).

• Soft Sealing (Rubber, PTFE): Zero leakage, but poor temperature resistance.

• Metal Sealing (Hard Sealing): Resistant to high temperature and high pressure, but may have a small amount of leakage.

• Special Working Conditions: High - sealing - performance valves are required for vacuum systems, and zero - leakage designs are needed for toxic/flammable media.

  
  

V. Operation Method

• Manual Operation: Suitable for small - diameter and low - frequency operations.

• Electric/Pneumatic/Hydraulic Operation: Suitable for remote control, high - frequency, or high - torque occasions (such as large - diameter butterfly valves).

• Automation Requirements: Control valves need to be equipped with positioners, and safety valves need interlock control.

  
  

VI. Material Selection

• Valve Body Material: Select according to the corrosion of the medium, temperature, and pressure:

• Cast Iron: For low - pressure and normal - temperature non - corrosive media.

• Cast Steel: For medium - high - pressure and high - temperature systems (such as steam).

• Stainless Steel (304/316): For corrosive media.

• Plastic (PVC, PP): For strong acid - and alkali - resistant media.

• Sealing Material: The temperature and corrosion resistance need to match the medium.

  
  

VII. Installation and Maintenance

• Installation Space: Butterfly valves and ball valves have a compact structure and are suitable for occasions with limited space.

• Maintenance Convenience: Split - type bonnet designs are convenient for maintenance, and for special media, the ability for on - line maintenance should be considered.

• Economy:

• Balance the initial cost and the life - cycle cost (LCC):

• Low - cost valves (such as cast - iron gate valves) may increase the total cost due to frequent maintenance.

• High - reliability valves (such as high - performance butterfly valves) may have a high initial investment but reduce downtime losses.

  
  

VIII. Standards and Regulations

Comply with industry standards (such as API, ASME, GB, ISO) and safety regulations.

• Special Industry Requirements: The food and pharmaceutical industries need to comply with hygiene standards (such as FDA), and nuclear power valves need to meet seismic design requirements.

IX. Environment and Safety

• Environmental Adaptability: Outdoor valves need to be rust - proof (such as epoxy coating), and materials for low - temperature environments need cryogenic treatment.

• Safety Design: Fire - proof structure (API 607 certification), anti - static design (suitable for flammable media).

  
  

X. Example of the Selection Process

• Determine the Working Condition Parameters: The medium is a corrosive acid solution, the temperature is 80°C, the pressure is 1.6 MPa, and flow regulation is required.

• Valve Type: Fluorine - lined globe valves or diaphragm valves with corrosion resistance are preferred.

• Material Selection: The valve body material is selected as CF8M (316 stainless steel), and the sealing material is selected as PTFE.

• Calculation of the Nominal Diameter: Calculate DN50 according to the flow formula.

• Operation Method: Equip with an electric actuator to achieve remote regulation.

XI. Common Mistakes and Avoidance

• Ignoring Medium Compatibility: For example, using ordinary stainless steel in a chlorine environment, while Hastelloy should be selected.

• Over - sizing/Under - sizing: This leads to poor regulation performance or excessive pressure loss, and verification through flow calculation is required.

• Neglecting Maintainability: In high - wear working conditions, the design does not reserve room for replacing seals.

Through systematic selection analysis, the valve performance can be maximally matched with the working - condition requirements to ensure the efficient and safe operation of the system. It is recommended to make the final decision in combination with the technical support of suppliers and industry experience.