14.07.2026 07:51
Selecting a ball valve should not be based only on pipe diameter or pressure class. The fluid properties, operating pressure, temperature, flow rate, connection type, body material, seat material, operating frequency, safety requirements and automation needs must all be evaluated together.
An incorrectly selected ball valve may result in leakage, excessive pressure loss, increased operating torque, premature wear, corrosion and unplanned plant shutdowns. Therefore, both the initial purchase cost and the total service life of the valve should be considered.
1. Determine the purpose of the valve
First, the function of the valve within the system must be clearly defined:
Complete flow shut-off
Pipeline isolation
Flow direction change
Mixing or diverting
Emergency shutdown
Automatic opening and closing
Maintenance isolation
Flow control
Standard ball valves are primarily designed for fully open or fully closed operation. When accurate flow regulation is required, V-port or segmented ball control valves should be considered.
Operating a standard ball valve continuously in a partially open position may concentrate flow velocity on certain areas of the ball and seats. This can cause erosion, vibration and premature seat damage, particularly under high differential pressure or with abrasive fluids.
2. Identify the fluid characteristics
The transported fluid is one of the most important selection criteria. Describing the medium only as water, gas or chemical may not be sufficient.
The following information should be defined:
Exact fluid name
Liquid, gas or two-phase condition
Chemical composition
Concentration
Density
Viscosity
Acidity or alkalinity
Corrosive properties
Solid particle content
Flammability
Toxicity
Crystallisation tendency
Freezing risk
Polymerisation tendency
Hygiene requirements
The body, ball, stem, seats, gaskets and O-rings must all be chemically compatible with the fluid.
Typical application examples
Clean water and utility systems:
Brass, cast iron, ductile iron, carbon steel or stainless-steel bodies may be suitable depending on pressure, temperature and water quality.
Natural gas and combustible gases:
Antistatic design, blowout-proof stem construction, low-emission sealing, fire-safe performance and compliance with applicable gas standards should be considered.
Steam:
Body, seat, packing and gasket materials must withstand the actual steam pressure and temperature. Standard PTFE seats may not be suitable for all steam applications.
Chemical fluids:
Stainless steel, special alloys or lined valves may be required. Fluid concentration and temperature must be evaluated together.
Abrasive or particle-containing fluids:
Reinforced polymer seats, metal seats, hard coatings or cavity-minimising designs may be necessary.
Oxygen, hydrogen, chlorine and cryogenic fluids:
Specially designed, cleaned, tested and certified valves should be used.
3. Determine operating and design pressure
The following pressure values should be identified:
Normal operating pressure
Maximum operating pressure
Design pressure
Test pressure
Pump shut-off pressure
Pressure surge
Water hammer
Maximum differential pressure across the closed valve
The PN or ASME Class marking alone is not sufficient. The actual allowable pressure depends on:
Body material
Operating temperature
Seat material
Valve construction
Manufacturer pressure-temperature ratings
A PN16 valve should not automatically be assumed to operate at 16 bar at every temperature. As the temperature increases, the allowable working pressure of the body and polymer seats may decrease.
An appropriate engineering safety margin should be included for process fluctuations, pressure surges, temperature changes and material ageing.
4. Check the operating temperature
Minimum, normal and maximum temperatures must be specified. Both fluid temperature and ambient temperature should be considered.
Temperature directly affects:
Body strength
Seat deformation
Elastomer life
Packing performance
Operating torque
Thermal expansion
Actuator performance
Leakage performance
Cryogenic applications may require extended stems, specialised sealing arrangements and cavity pressure-relief systems.
High-temperature applications may require reinforced polymers, PEEK, graphite seals or metal-seated constructions.
The manufacturer’s pressure-temperature chart must always be checked for the exact valve model.
5. Calculate valve size and flow capacity
The valve nominal diameter is often selected to match the pipe size. However, this approach may not be sufficient in high-flow, gas, steam or control applications.
The following parameters should be reviewed:
Required flow rate
Inlet pressure
Outlet pressure
Allowable pressure drop
Fluid density
Fluid viscosity
Gas temperature and compressibility
Kv or Cv coefficient
Flow velocity
Cavitation risk
Noise risk
Kv represents the flow rate of water through a valve at a pressure drop of 1 bar in metric units.
Cv represents a similar flow-capacity value using US customary units.
Valves of the same nominal diameter may have different Kv or Cv values depending on their internal design.
When the valve is undersized
Pressure loss increases.
Flow velocity becomes excessive.
Noise and vibration may occur.
Ball and seat erosion may accelerate.
Pump energy consumption may increase.
When the valve is oversized
Control accuracy may decrease.
Operating torque and actuator cost may increase.
The valve may operate mainly near the closed position in control service.
6. Select full-bore or reduced-bore construction
Full-bore ball valve
The ball opening is approximately equal to the internal diameter of the pipe.
Advantages include:
Low pressure loss
High flow capacity
Reduced turbulence
Better suitability for pigging
Reduced particle accumulation
Lower pumping energy losses
Full-bore valves are generally preferred in high-flow lines, viscous-fluid systems and pipelines requiring internal cleaning or pigging.
Reduced-bore ball valve
The ball opening is smaller than the internal diameter of the pipe.
Advantages include:
Compact construction
Lower weight
Lower initial cost
Smaller actuator requirements in certain applications
Reduced-bore valves may be suitable where pressure loss is not critical. However, the additional pressure drop should be calculated.
7. Select floating-ball or trunnion-mounted design
Floating-ball valve
In a floating-ball valve, the ball is supported mainly by the seats and is allowed to move slightly under line pressure. Pressure pushes the ball against the downstream seat to create sealing.
Typical applications include:
Small and medium diameters
Low and medium pressures
General industrial services
Water, air, oil and compatible process fluids
Cost-sensitive isolation duties
As size and pressure increase, the load applied to the downstream seat and the operating torque may increase.
Trunnion-mounted ball valve
In a trunnion-mounted design, the ball is mechanically supported at the top and bottom. The ball remains fixed while the seats move toward the ball.
Typical applications include:
Large-diameter pipelines
High pressure
Oil and natural gas pipelines
High differential pressure
Lower operating torque requirements
Double block and bleed systems
Critical process services
Trunnion designs are often preferred where high pressure, large size, controlled seating forces and reduced torque are required.
8. Select the body material
Brass
Suitable for:
Clean water
Air
Small-bore utility systems
General low- and medium-pressure installations
Fluid compatibility, potable-water requirements and dezincification resistance should be checked.
Cast iron
Suitable for:
Water systems
Heating and cooling systems
General low- and medium-pressure applications
Mechanical impact, external loads and high-temperature limitations must be considered.
Ductile iron
Suitable for:
Water distribution
Fire-protection systems
General industrial services
Applications requiring greater mechanical strength than grey cast iron
Carbon steel
Suitable for:
Oil and natural gas
Steam
Process plants
Medium- and high-pressure systems
Industrial pipelines
Corrosion allowance and internal component compatibility should be evaluated.
Stainless steel
Suitable for:
Chemical and petrochemical plants
Food and beverage processing
Corrosive fluids
Marine environments
Clean and hygienic processes
Different stainless-steel grades such as 304, 316, 316L and duplex should not be treated as identical materials.
Special alloys
Duplex, super duplex, Alloy 20, Monel, Hastelloy and nickel alloys may be required for:
Chloride-rich fluids
Strong acids
Seawater
Hydrogen sulphide
High temperatures
Highly corrosive chemicals
Material selection should be made together with the valve manufacturer and, where necessary, a corrosion specialist.
9. Evaluate the ball and stem materials
The suitability of the body material does not automatically mean that the ball and stem materials are suitable.
The following should be reviewed:
Base material of the ball
Surface coating
Surface hardness
Surface finish
Stem material
Galvanic compatibility
Corrosion resistance
Erosion resistance
Antistatic connection
Blowout-proof stem design
Hard chrome, nickel-based coatings, tungsten carbide and chromium carbide may be considered for severe abrasive service.
10. Select the seat and sealing materials
Seat material has a major influence on leakage performance, temperature capability and operating torque.
Material General characteristics Typical application
PTFE Low friction and broad chemical resistance Water, air, gas and general chemical service
RPTFE Higher mechanical strength than standard PTFE Higher pressure, temperature and cycling
TFM Low deformation and good chemical resistance High-integrity process sealing
PEEK High temperature and mechanical resistance High-pressure and severe service
UHMWPE Good abrasion resistance Particle-containing and selected chemical services
PCTFE Low gas permeability and good low-temperature performance Gas and cryogenic applications
Metal seat Suitable for extreme temperature and abrasive media Steam, ash, powder and slurry service
The final material selection must be confirmed using the manufacturer’s chemical-compatibility and pressure-temperature data.
Common elastomers
NBR
EPDM
FKM
FFKM
Silicone
EPDM may be suitable for many water applications but unsuitable for petroleum-based fluids. FKM may provide good oil and chemical resistance but is not universally compatible with every medium or temperature.
11. Select the connection type
Threaded connection
Suitable for:
Small diameters
General installations
Compact systems
Economical applications
Suitability should be carefully reviewed for high temperature, hazardous fluids and severe vibration.
Flanged connection
Suitable for:
Medium and large diameters
Industrial installations
Systems requiring easy removal
High pressure classes
Critical pipelines
The flange standard, pressure class, facing type, bolt pattern and mating flange must be compatible.
EN, DIN and ASME flanges are not necessarily interchangeable even when the nominal diameter is the same.
Socket-weld connection
Suitable for:
Small-diameter high-pressure systems
Process plants
Applications requiring welded leak-tight connections
Butt-weld connection
Suitable for:
Long-distance pipelines
High-pressure and high-temperature systems
Applications where external leakage must be minimised
Installations that will remain in service for long periods without removal
The manufacturer’s welding instructions must be followed to avoid heat damage to the seats.
Hygienic connections
Clamp, orbital-weld and other sanitary connections may be required in food, beverage, pharmaceutical and biotechnology applications.
Internal surface finish, cleanability and dead-leg reduction should also be specified.
12. Select the body construction
One-piece valve
Compact
Economical
Low number of external leakage paths
Limited maintenance capability
Two-piece valve
Widely used in general industry
Available with threaded or flanged ends
Balanced cost and maintenance performance
Three-piece valve
Easier seat and seal replacement
Suitable for welded piping
Centre body may be removed without cutting the pipeline
Useful in processes requiring frequent maintenance
Top-entry valve
Internal components may be accessed from the top
Suitable for critical or large-diameter pipelines
May allow in-line maintenance without removing the valve body from the piping
13. Select two-way, three-way or multi-way configuration
Two-way ball valve
Used for standard shut-off and isolation.
Three-way ball valve
Used for diverting, mixing or distributing flow.
L-port:
Usually directs one inlet toward one of two outlets.
T-port:
May allow mixing, diverting or multiple connection combinations.
When selecting a three-way valve, the required port positions and operating sequence should be shown on a flow diagram.
14. Select manual or automated operation
Manual lever operation
Suitable for:
Small and medium diameters
Low operating torque
Infrequent operation
Accessible installation points
Gear-operated valve
Suitable for:
Large diameters
High torque
Slow and controlled operation
Reduction of water-hammer risk
Pneumatic actuator
Suitable for:
Fast opening and closing
Frequent cycling
Factory automation
Hazardous areas
Spring-return fail-safe operation
Electric actuator
Suitable for:
Remote operation
Locations without compressed air
Slow and controlled movement
Position feedback
Modulating service
Hydraulic actuator
Suitable for:
Very high torque
Large pipeline valves
Critical emergency shutdown systems
Actuator selection should consider:
Maximum valve torque
Differential pressure
Fluid properties
Temperature
Operating frequency
Long periods without movement
Safety factor
Required opening and closing time
15. Determine the fail-safe position
For automated valves, the position of the valve after loss of power or air must be determined.
Fail-close: The valve closes when energy is lost.
Fail-open: The valve opens when energy is lost.
Fail-in-place: The valve remains in its current position.
The correct fail-safe position must be determined through process risk analysis.
Fuel lines may require fail-close operation, whereas certain cooling-water systems may require fail-open operation.
16. Evaluate sealing direction and body-cavity pressure
Not every ball valve provides identical sealing performance in both directions.
The following should be checked:
Unidirectional or bidirectional sealing
Preferred flow direction
Self-relieving seat
Double-piston-effect seat
Double block and bleed
Body-cavity vent
Drain connection
Pressure-balancing hole
Thermal expansion of trapped fluid
When the valve is closed, fluid can become trapped between the ball and body. Temperature increase may generate very high pressure in this closed cavity.
Body-cavity pressure relief is especially important in liquid, LPG, LNG and cryogenic services.
17. Check fire safety and antistatic requirements
For combustible fluids, the following features may be required:
Fire-safe design
Antistatic device
Blowout-proof stem
Graphite secondary sealing
Controlled leakage performance after fire exposure
Fire-tested body and closure construction
A product described as “fire-safe designed” should not automatically be treated as a valve that has been tested and certified to a recognised fire-test standard.
The certificate must cover the offered model, size, pressure class and sealing construction.
18. Define fugitive-emission requirements
For natural gas, hydrocarbon, toxic-gas and volatile-organic-compound services, atmospheric leakage from the valve is a major consideration.
The following leakage paths should be assessed:
Stem packing
Body joints
Cover gaskets
Drain and vent connections
Sealant injection fittings
The required emission class, temperature class and mechanical-cycle class should be specified.
19. Select the applicable standards
Frequently referenced standards include:
ASME B16.34: Valve pressure-temperature ratings, materials, design and marking
API 608: Metal ball valves with flanged, threaded and welding ends
ISO 17292: Metal ball valves for petroleum, petrochemical and natural-gas industries
API 6D: Pipeline and piping valves
ISO 5211: Actuator mounting interfaces for part-turn valves
ISO 10497: Fire type-testing requirements
ISO 15848: Fugitive-emission measurement and classification
API 598: Valve inspection and testing
The project specification should clearly identify the applicable design, testing, certification and documentation requirements.
20. Evaluate special applications separately
Natural gas
Gas-compatible seats and seals
Antistatic construction
Low fugitive emissions
Fire-safe performance
Appropriate gas approvals
Safe operation at full differential pressure
Steam
Actual pressure and temperature
Saturated or superheated steam
High-temperature seat material
Thermal cycling
Packing and body-gasket compatibility
Cryogenic service
Extended bonnet or stem
Low-temperature materials
Body-cavity pressure relief
Special cryogenic testing
Appropriate material certificates
Vacuum
Stem sealing suitable for inward leakage control
Low-permeability seats and seals
Manufacturer approval for the required vacuum level
Abrasive fluid and slurry
Metal seats
Hard-coated ball and seats
Reduced-cavity body
Drain and flushing connections
Controlled operating speed
Food and pharmaceutical processing
Hygienic body construction
Reduced dead volume
Suitable internal surface roughness
Food-contact-approved seals
CIP or SIP compatibility
Required hygienic certificates
21. Review maintenance and spare-parts availability
The following questions should be answered:
Can seats and seals be replaced?
Are spare-parts kits available?
Can maintenance be performed without removing the valve from the pipeline?
Can an actuator be added later?
Is the stem packing adjustable?
Is technical support available?
Is the product traceable?
Are material certificates available?
Three-piece and top-entry designs may provide lower life-cycle costs in systems requiring frequent maintenance.
22. Check installation conditions
Before installation:
The pipeline should be cleaned.
Welding slag and debris should be removed.
Flanges should be properly aligned.
The valve should not be used to correct pipe misalignment.
Correct gaskets should be used.
Bolts should be tightened in a cross pattern.
Heavy actuators should be independently supported.
Flow-direction markings should be followed.
Welding heat should be controlled.
An opening and closing test should be performed before commissioning.
The valve lever or actuator should not be used as a lifting point.
23. Common ball-valve selection mistakes
Selecting only according to pipe diameter
Considering PN or Class rating alone
Not specifying maximum temperature
Not specifying chemical concentration
Ignoring seat and seal compatibility
Confusing full-bore and reduced-bore construction
Using a standard ball valve as a precision control valve
Selecting an actuator without a safety margin
Ignoring fire-test and fugitive-emission requirements
Selecting flanges only according to nominal diameter
Ignoring trapped cavity pressure
Using standard soft seats for abrasive media
Closing the valve too quickly where water hammer is possible
Ignoring maintenance and spare-parts availability
Failing to verify that certificates cover the offered product
24. Technical information required before ordering
Fluid:
Fluid concentration:
Normal operating pressure:
Maximum operating pressure:
Design pressure:
Minimum temperature:
Normal operating temperature:
Maximum temperature:
Flow rate:
Pipe size:
Connection standard:
Pressure class:
Full bore or reduced bore:
Floating or trunnion design:
Body material:
Ball and stem material:
Seat material:
Manual or actuated operation:
Actuator power source:
Fail-safe position:
Opening and closing time:
Operating cycles per hour or day:
Fire-test requirement:
Fugitive-emission requirement:
Required tests and certificates:
Installation environment:
Hazardous-area classification:
Special coating or painting requirement:
Conclusion
Correct ball-valve selection is essential for safe, efficient and long-lasting plant operation.
The selection process should consider not only DN and PN values but also:
Fluid characteristics
Actual pressure and temperature
Flow capacity
Bore construction
Body and seat materials
Valve design
Connection type
Actuation torque
Safety requirements
Applicable standards
For critical processes, valve selection should be performed together with the valve manufacturer or an experienced engineering team using detailed process data and project specifications.
VANEX VALVE provides technical evaluation and product-selection support for water, natural gas, oil, steam and industrial process applications.
Website: www.vanexvalve.com
E-mail: info@vanexvalve.com
