Principles of valves ball valve selection
media characteristics
Corrosion resistance: select corrosion-resistant materials (such as 316L stainless steel, Hastelloy) according to the chemical properties of the medium (such as acid, alkali, organic solvent).
Cleanliness: hard sealing (metal to metal) or a specially designed anti-clogging structure should be selected for particles or high viscosity media.
Phase: gas, liquid, or gas-liquid mixture medium needs to be designed for sealing and structure.
working condition
Pressure: high pressure (PN≥16MPa) should select a fixed ball valve, and low pressure can select a floating ball valve.
Temperature: high temperature (> 200℃) requires metal sealing, low temperature (<-50℃) requires cryogenic treatment materials (such as austenitic stainless steel).
Flow characteristics: Full port ball valve (Full Port) is used for applications requiring low flow resistance, and reduced port ball valve (Reduced Port) is used for applications where pressure loss is allowed.
Valve materials
Valve body material:
Ordinary working conditions: cast steel (WCB), stainless steel (CF8/CF8M).
Strong corrosion: duplex steel, titanium alloy.
sealing material ：
Conventional temperature: PTFE (temperature resistance ≤180℃), PPL (temperature resistance ≤300℃).
High temperature/wear: metal seals (e.g. tungsten carbide coating)
structural style
Floating ball valve: suitable for small diameter (DN≤200mm), medium and low pressure, relying on the medium pressure to press the ball seal.
Trunnion ball valve: large diameter (DN≥200mm), high pressure or high precision control, the ball is fixed by the upper and lower shaft, less torque.
V type ball valve: used when flow is to be adjusted, with approximate percentage flow characteristics.
Sealing class
Ordinary working condition: ISO 5208 Class VI (soft seal).
Strict working conditions: Class V or metal sealed zero leakage (e.g. API 6D standard).
mode of operation
Manual: For occasions where frequent operation is not required, it can be equipped with worm gear reducer (large diameter valve).
Automatic control: Pneumatic: explosion-proof environment (e.g., petrochemical industry).
Electric: need precise control (e.g., electricity, water treatment).
Fluid power: high thrust requirements (e.g., main valve for long distance pipelines).
Standards and certification
Industry standards: API 6D (petroleum and gas), GB/T 12237 (general), ASME B16.34 (pressure and temperature rating).
Special certification: SIL (Safety integrity level), TA-Luft (low emission).
Economics and maintenance
Total life cost: includes procurement, installation, maintenance and downtime losses.
Maintain convenience: modular design, online maintenance capability (such as double cut-off discharge function).
Valves Ball valve selection
Define working condition parameters
Prepare parameter table, including: medium name, temperature range, pressure range (design pressure/work pressure), flow rate requirement, pipe size (DN/inch), connection standard (flange/thread), action frequency, etc.
Determine the valve type
Function selection:
Switch valve: standard ball valve.
Regulating valve: V-type ball valve or intelligent valve with locator.
By structure:
Three-way, L-type/T-type channel: used for medium distribution.
Top Entry: easy to maintain online.
Material and seal fit
Valve body/ball material: Refer to NACE MR0175 standard (including H2S environment).
Valve seat/seal:
Food grade medium: FDA certified materials (e.g., EPDM+PTFE).
Wear medium: Stellite cemented carbide welding.
Connection and end face treatment
Flange connection: RF (surrounding surface), RTJ (ring connection), FF (full plane).
Welding end: butt welding (BW) is selected for thick wall pipes, and post-weld heat treatment should be considered.
Thread connection: NPT, BSPT, suitable for small diameter low pressure pipeline.
Drive mode optional
Pneumatic actuator: the air source pressure (0.4~0.7MPa) and double action/single action (fault safety type) should be specified.
Electric actuator: protection class (IP67/IP68), torque matching (opening and closing torque calculation required).
Manual operation: large diameter valve with gearbox (DN300 or above).
Performance verification
Flow calculation: verify whether Cv value meets the process requirements (Cv=Q√ (SG/ΔP)).
Pressure loss: Ensure that the pressure drop of the reducing valve is within the allowable range.
Anti-cavitation/flashing: high flow rate medium requires special design of flow channel or multi-stage pressure reduction structure.
Supplier evaluation
Qualification: API 607 fire protection certification, ISO 15848 low leakage certification.
Case reference: industry application performance (e.g., LNG terminal, chemical plant).
After-sales service: spare parts inventory, technical support response time.
Comprehensive cost analysis
Initial cost: valve, actuator, and accessories (such as limit switches and solenoid valves).
Operation and maintenance cost: the frequency of seal replacement and failure rate during the life cycle.
Technical confirmation and testing
Factory acceptance test (FAT): including sealing test (high pressure water/air), operation torque test.
Special tests: cryogenic treatment, fire resistance test (API 607).
Installation and debugging
Flow direction: ensure that the installation direction of the valve is consistent with the flow direction of the medium (some ball valves have directional requirements).
Drive mechanism calibration: electric valve needs to be adjusted for opening signal (4~20mA) and position feedback.
Common selection mistakes
Excessive pursuit of high material: non-corrosive medium (such as water, air) can be selected carbon steel valve body, to avoid unnecessary costs.
Neglect dynamic sealing: valves with frequent operation should pay attention to valve stem sealing (e.g., graphite packing vs. spring-loaded PTFE).
Neglect thermal expansion: high temperature pipeline should calculate the thermal displacement of valve body and pipeline to prevent stress damage.
