Guides to help you select the right valve

Two of the most common isolation valves in process plants — and yet engineers still frequently specify the wrong one. The consequences range from unnecessary cost to premature failure, excessive pressure drop or — in the worst case — a valve that doesn't hold up in service at all.

Here is how to choose correctly, based on the parameters that actually matter.

The core difference

A ball valve uses a rotating sphere with a through-bore to control flow. When fully open, the bore aligns with the pipe and presents essentially zero obstruction — giving very low pressure drop and true full-bore flow. The seat and ball must seal against each other at line pressure.

A butterfly valve uses a rotating disc that sits in the flow path even when open. This means there is always some obstruction and a higher pressure drop. However, butterfly valves are mechanically much simpler, require less torque to operate at larger sizes, and cost significantly less in larger diameters.

When to use a ball valve

• Line sizes up to DN200 (above this, cost and torque favour butterfly valves)
• Media that requires zero-dead-leg — pharmaceutical, food and beverage processes
• High pressure service where full bore and tight shut-off are both required
• Frequent cycling — ball valves are more durable under high cycle duty
• 3-way diverting or mixing service
• Cryogenic service, where disc-in-flow designs cause operational problems

When to use a butterfly valve

• Line sizes DN200 and above — cost savings become very significant
• Low to moderate pressure service (typically below 16 bar for standard designs)
• Water, air, non-aggressive slurries and general utility service
• Space-constrained installations where the short face-to-face is advantageous
• Throttling duty where a ball valve would cavitate at partial opening
• Budget-sensitive projects where tight shut-off is not critical

Side-by-side comparison

Parameter	Ball Valve	Butterfly Valve
Typical size range	DN15–DN200	DN50–DN2000+
Pressure drop (full open)	Very low (full bore)	Moderate (disc obstructs)
Shut-off class	Class VI (bubble-tight)	Class IV–V (double eccentric)
Cycle life	High (100,000+ cycles)	Moderate–high
Relative cost (large bore)	High	Low
Throttling suitability	Poor	Good (with double eccentric)
High pressure service	Excellent	Limited (standard designs)

Special cases

Lined valves for corrosive media

Both ball and butterfly valves can be supplied PTFE or FEP-lined for corrosive acid and alkali service. In lined configurations, the butterfly valve offers a significant cost advantage at larger sizes. For very aggressive media at higher pressures, however, the lined ball valve remains the more reliable choice because the liner is less stressed.

Actuated assemblies

Both valve types are equally suitable for pneumatic or electric actuation. The choice of actuator type (and its torque rating) will differ — ball valves typically require higher breakaway torque than butterfly valves at the same line pressure. Always ask your manufacturer to confirm the actuator sizing against actual line pressure, not just nominal ratings.

Choosing the wrong actuator type is one of the most common — and most costly — mistakes in valve automation. An undersized actuator will fail to stroke the valve at line pressure. An oversized one wastes energy and puts unnecessary stress on the valve stem. And choosing pneumatic when you have no reliable instrument air supply guarantees a maintenance headache.

Here is the structured approach our engineers use when specifying actuated valve assemblies.

Step 1: Understand the required torque

Every actuator must be sized against the valve's breakaway torque — the force needed to unseat and begin moving the valve disc or ball from its closed position under line pressure. This is not the same as running torque and it is always higher.

A common mistake is to use the valve manufacturer's torque table at zero differential pressure. Always calculate at your actual maximum differential pressure, and then apply a safety factor of at least 25–30% on top.

Step 2: Pneumatic or electric?

Criterion	Pneumatic Actuator	Electric Actuator
Power supply	Instrument air (4–7 bar)	Electrical (24VDC to 415VAC)
Cycle speed	Fast (seconds)	Slower (10–60 seconds typical)
Fail-safe action	Simple spring-return	Requires battery/capacitor backup
High cycle duty	Excellent	Heat build-up limits cycle rate
Explosion-proof	Inherently safe	EEx certified units available
Modulating control	With positioner (excellent)	With positioner (excellent)
Remote location (no air)	Not suitable	Preferred
Relative cost	Lower	Higher

When to choose pneumatic

• Instrument air is reliably available at the valve location
• Fast stroking speed is required (ESD valves, on/off duty)
• High cycle frequency (pilot valves, control loops)
• Spring-return fail-safe (fail-open or fail-closed) is required for safety
• The environment is hazardous (ATEX Zone 1/2) and simplicity is preferred

When to choose electric

• No instrument air supply at the valve location
• Remote or unmanned locations with only electrical power available
• Multi-turn applications (gate valves, globe valves) where pneumatic is impractical
• Position accuracy over a long stroke is needed without a separate positioner
• Energy efficiency is a priority — electric actuators consume power only during movement

Step 3: Define the fail-safe action

For any safety-critical valve, the fail-safe action must be defined before selecting the actuator: should the valve fail open, fail closed or fail in last position on loss of power or air?

For pneumatic actuators, spring-return provides reliable fail-safe action without any additional components. For electric actuators, fail-safe requires a battery pack or capacitor bank — which adds cost and requires maintenance.

Solenoid valves are among the most frequently mis-specified components in a process plant. They are simple in concept but the selection involves more parameters than most buyers realise — and getting them wrong means early failure, leakage or a valve that simply won't open under line pressure.

Ask yourself these five questions before placing any solenoid valve order.

1. What is the media, and is it compatible with the internals?

The media flowing through the valve determines the body material, seal elastomer and whether a direct-operated or pilot-operated design is appropriate.

• Water, air: Brass or stainless steel body, NBR or EPDM seal
• Steam: Stainless steel body, PTFE seat — ensure the coil is rated for the ambient temperature near the valve
• Acids / alkalis: PTFE-lined stainless steel, Viton or PTFE seal
• Oils / hydraulic: Nitrile (NBR) seal — verify compatibility with specific oil grade
• Food / pharma: SS316L body, FDA-approved EPDM or silicone seal

2. What is the operating pressure and differential pressure?

This determines whether you need a direct-operated or pilot-operated design — and it is the single most common source of solenoid valve failures.

Direct-operated valves use the solenoid force alone to open the orifice. They work from zero bar differential pressure upwards and are suitable for low flow, small orifice applications. Pilot-operated valves use line pressure to assist opening — they are far more common for larger orifices but require a minimum differential pressure (typically 0.5 bar) to function. Ordering a pilot-operated valve for a gravity-flow line with near-zero differential pressure will result in a valve that fails to open.

3. What is the required orifice size and Cv?

The flow coefficient Cv determines how much flow the valve passes at a given differential pressure. An undersized Cv creates excess pressure drop; an oversized Cv wastes money and may cause control instability. Calculate your required Cv from your flow rate and differential pressure — your manufacturer should be able to confirm this for you.

4. What coil voltage and protection rating do you need?

• Coil voltage: 24VDC is standard for control system integration; 230VAC for direct panel wiring. Confirm with your electrician before ordering — the coil cannot be changed in the field on most designs.
• IP rating: IP65 is standard for indoor industrial. IP67 or IP68 for outdoor or wash-down environments. ATEX/Ex-proof for hazardous area Zone 1 or Zone 2.
• Duty cycle: Continuous duty (100% ED) coils for valves that stay energised for long periods. Intermittent duty coils run hot and fail prematurely on continuous energisation.

5. What is the required function — 2-way or 3-way?

A 2/2-way (2-way) solenoid valve has one inlet and one outlet — it either opens or closes the flow path. This is the most common type for on/off isolation duty.

A 3/2-way (3-way) solenoid valve has three ports — typically used to pilot pneumatic actuators (supply pressure to one side, exhaust the other) or for diverting flow between two outlets.

A 5/2-way solenoid valve has five ports — the standard pilot valve for double-acting pneumatic actuators, providing supply and exhaust to both sides of the actuator cylinder.