Principles and steps for ball valve selection

1. Basic principles for ball valve selection

Medium characteristics
Corrosiveness: 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 seals (metal to metal) or specially designed anti-blocking structures are required for medium containing particles or high viscosity.
Phase state: Gas, liquid or gas-liquid mixed medium requires targeted design of seals and structures.

Working conditions
Pressure: Fixed ball valves are required for high pressure (PN≥16MPa), and floating ball valves are optional for low pressure.
Temperature: Metal seals are required for high temperature (＞200℃), and deep-cold treated materials (such as austenitic stainless steel) are required for low temperature (＜-50℃).
Flow characteristics: Full-bore ball valves (Full Port) are used in situations where low flow resistance is required, and reduced-bore ball valves (Reduced Port) are suitable for scenarios where pressure loss is allowed.

Valve material
Body material:General working conditions: cast steel (WCB), stainless steel (CF8/CF8M).
Strong corrosion: duplex steel, titanium alloy.
Sealing material:
Normal temperature: PTFE (temperature resistance ≤180℃), PPL (temperature resistance ≤300℃).
High temperature/wear: metal seal (such as tungsten carbide spraying)

Structural form
Floating ball valve: suitable for small diameter (DN≤200mm), medium and low pressure, relying on medium pressure to compress the ball seal.
Fixed ball valve: large diameter (DN≥200mm), high pressure or high precision control occasions, the ball is fixed by the upper and lower shafts, and the torque is smaller.
V-type ball valve: selected when the flow needs to be adjusted, with an approximate equal percentage flow characteristic.

Sealing level
General working conditions: ISO 5208 Class VI (soft seal).
Severe working conditions: Class V or metal seal zero leakage (such as API 6D standard).

Operation mode
Manual: used in occasions where frequent operation is not required, and can be equipped with a worm gear reducer (large-diameter valve).
Automatic control: Pneumatic: explosion-proof environment (such as petrochemical industry).
Electric: precise control is required (such as electricity, water treatment).
Hydraulic: high thrust demand (such as long-distance pipeline main valve).

Standards and certifications
Industry standards: API 6D (oil and gas), GB/T 12237 (general), ASME B16.34 (pressure and temperature rating).
Special certifications: SIL (safety integrity level), TA-Luft (low fugitive emissions).

Economy and maintenance
Life cycle cost: including procurement, installation, maintenance and downtime losses.
Easy maintenance: modular design, online maintenance capabilities (such as double cut-off discharge function).

2. Steps for ball valve selection

Clear working parameters
Prepare a parameter table, including: medium name, temperature range, pressure range (design pressure/working pressure), flow requirements, pipe size (DN/inch), connection standard (flange/thread), action frequency, etc.

Determine valve type
Select by function:
Switch valve: standard ball valve.
Regulating valve: V-type ball valve or smart valve with positioner.
Select by structure:
Three-way, L-type/T-type channel: used for medium distribution.
Top loading (Top Entry): convenient for online maintenance.

Material and seal matching
Valve body/ball material: refer to NACE MR0175 standard (including H2S environment).
Valve seat/seal:
Food grade medium: FDA certified material (such as EPDM+PTFE).
Abrasive medium: Stellite carbide surfacing.

Connection method and end surface treatment
Flange connection: RF (raised face), RTJ (ring connection), FF (full plane).
Welding end: Butt welding (BW) is used for thick-walled pipes, and post-weld heat treatment needs to be considered.
Threaded connection: NPT, BSPT, suitable for small-diameter low-pressure pipes.

Drive mode selection
Pneumatic actuator: The air source pressure (0.4~0.7MPa) and double-acting/single-acting (fail-safe type) need to be specified.
Electric actuator: Protection level (IP67/IP68), torque matching (opening and closing torque needs to be calculated).
Manual operation: Large-diameter valves are equipped with gearboxes (such as DN300 and above).

Performance verification
Flow calculation: Verify whether the Cv value meets the process requirements (Cv=Q√(SG/ΔP)).
Pressure loss: Ensure that the pressure drop of the reduced-diameter valve is within the allowable range.
Anti-cavitation/flash: High-velocity media require specially designed flow channels or a multi-stage pressure reduction structure.

Supplier evaluation
Qualification review: API 607 ​​fire protection certification, ISO 15848 low leakage certification.
Case reference: Application performance in the same industry (such as LNG receiving stations, chemical plants).
After-sales service: spare parts inventory, technical support response time.

Comprehensive cost analysis
Initial cost: valve + actuator + accessories (such as limit switch, solenoid valve).
Operation and maintenance cost: expected seal replacement frequency and failure rate within the life cycle.

Technical confirmation and testing
Factory acceptance test (FAT): including sealing test (high pressure water/gas), operating torque test.
Special tests: low temperature cryogenic treatment, fire resistance test (API 607).

Installation and commissioning
Flow direction identification: ensure that the valve installation direction is consistent with the medium flow direction (some ball valves have direction requirements).
Drive mechanism calibration: electric valves need to debug the opening signal (4~20mA) and position feedback.

3. Common selection misunderstandings

Excessive pursuit of high material: non-corrosive media (such as water, air) can use carbon steel valve body to avoid unnecessary costs.
Ignore dynamic seals: Valves that are frequently operated need to pay attention to stem seals (such as graphite packing vs. spring-loaded PTFE).
Ignore thermal expansion: High-temperature pipelines need to calculate the thermal displacement of the valve body and pipeline to prevent stress damage.