Butterfly Valve Guide

How they work, the main types and how to choose one

A butterfly valve is one of the simplest and most widely used valves in industry. It is light, compact and inexpensive for its size, and it can isolate a line or regulate flow. This guide explains how butterfly valves work, the main types, where they are a good choice and where they are not, and what to check before you buy one.

On this page: How it works · Types · Butterfly vs ball and gate valves · Seat materials · Operation · How to choose · Installation tips · Questions

How a Butterfly Valve Works

A butterfly valve has a round disc mounted on a shaft across the bore of the valve. Turning the shaft a quarter turn (90 degrees) swings the disc from fully closed, where it seals against the seat, to fully open, where it lies edge-on to the flow.

In most general-purpose valves the seat is a rubber liner that lines the body and also seals against the pipe flanges, so no separate flange gaskets are needed. Only the disc and the liner touch the fluid, which is why the body can be ductile iron while the disc and liner are chosen for the medium.

Because the disc can be held part-open, a butterfly valve can also regulate flow, especially between about 30 and 70 degrees open.

Types of Butterfly Valve

Most industrial butterfly valves are concentric, resilient-seated valves: the shaft passes through the centre of the disc and the disc seals against a rubber or PTFE liner. They differ mainly in how they fit into the pipeline.

Type	How it fits	Typical use
Wafer	Clamped between two pipe flanges by long bolts or studs passing outside the valve body	The most common and economical type for general isolation and control
Lug	Threaded lugs around the body; each flange is bolted to the valve separately	Where the pipe on one side must be removed while the valve stays in place
Double flanged	Its own flanges, bolted to the pipe flanges like a section of pipe	Large sizes, water mains and heavy-duty lines
PTFE-lined	Wafer or lug body with a PTFE liner and an encapsulated disc	Acids, chlorine, solvents and other corrosive or high-purity fluids
High-performance (offset)	Disc offset from the shaft so it lifts off the seat as it opens	Higher pressures and temperatures, steam and hydrocarbons

IPT supplies Vamein concentric wafer, lug, flanged and PTFE-lined (Galactic) valves. See the Vamein butterfly valve range.

Butterfly Valve vs Ball Valve vs Gate Valve

The butterfly valve's big advantages are size and weight. A butterfly valve is a fraction of the weight and face-to-face length of a gate or globe valve of the same size, which makes it cheaper to buy, easier to support and quicker to install, and the difference grows with pipe size.

	Butterfly valve	Ball valve	Gate valve
Weight and length	Lightest and shortest	Heavier and longer in large sizes	Heaviest and longest
Cost in large sizes	Lowest	High	High
Operation	Quarter turn	Quarter turn	Many turns
Flow control	Good for regulating	On/off; special designs for control	On/off only
Bore when open	Disc stays in the flow	Full bore available	Full bore
Pigging or rodding the line	Not possible	Possible with full bore	Possible
Best for	Water, air, gases, chemicals and powders in medium to large sizes at moderate pressure	Smaller sizes, higher pressures, tight shut-off	Isolation where full bore is needed

Butterfly valves are less suited to very high pressures and temperatures (unless a high-performance design is used), to lines that need a clear bore for pigging, and to throttling at very small openings, where cavitation and wear can occur.

Seat Materials

The seat (liner) is the part most likely to fail if it is wrongly chosen. Select it for the fluid first, then check the temperature: a liner run close to its limit ages much faster.

Seat material	Good for	Approximate temperature range
EPDM	Water, air, many dilute acids and alkalis	-15 to +100°C
High-temperature EPDM	Hot water	-15 to +120°C
NBR (nitrile)	Oils, fuels, gas	-15 to +100°C
Viton (FKM)	Hydrocarbons, solvents, higher temperatures	-20 to +180°C
Silicone	Very low and high temperatures	-40 to +180°C
PTFE	Strong chemicals and high-purity duties	-40 to +200°C

Temperature ranges are typical for Vamein liners; intermittent peaks can be a little higher. Always confirm chemical compatibility for your medium.

Ways to Operate a Butterfly Valve

Lever: simple and quick, usually up to about DN200 to DN300, with notched positions for regulating
Gearbox and handwheel: for larger valves or where the flow pushes on the disc; self-locking, with a position indicator
Chain wheel: a gearbox with a chain-driven wheel for valves mounted high up
Pneumatic actuator: fast on/off or, with a positioner, modulating control; spring-return versions fail safe on loss of air
Electric actuator: on/off or modulating from a 4-20 mA signal, for example Beck electric actuators for precise, continuous control

Valves with an ISO 5211 top flange can be motorised later by swapping the lever or gearbox for a standard actuator.

How to Choose a Butterfly Valve

What to have ready when you ask for a price

Size (DN or inches) and the flange standard: EN 1092 PN10/PN16, ANSI Class 150 or BS 10 Table D/E. See the butterfly valve size chart
Medium: what flows through the valve, including any solids or chemicals
Pressure and temperature: normal and maximum
Duty: isolation, regulating, or both; how often it operates
Body style: wafer, lug (essential if the valve may be at the end of a line) or flanged
Materials: body, disc and seat to suit the medium
Operation: lever, gearbox, chain wheel or actuator, and the control signal for an actuator
Special requirements: ATEX zone, drinking water, food contact, or certificates

Need a butterfly valve? We supply the Vamein range from DN50 to DN2000. Sizes up to DN350 are typically delivered in about 10 days from order and payment. Request a quotation or see the Vamein range.

Installation Tips

Insert the valve with the disc slightly open, so the disc edge sits inside the body and is not damaged by the flanges
Do not fit extra gaskets with rubber-lined valves: the liner is the flange seal
Centre the valve between the flanges before tightening, and tighten the bolts evenly in a cross pattern
Check the disc can open fully without touching the pipe, a reducer, a check valve or another fitting next to it
Where possible, keep a few pipe diameters of straight pipe upstream of a regulating valve, and fit large valves with the shaft horizontal on dirty or slurry duties
Never weld the pipe near a valve that is already fitted: heat damages the liner

Always follow the manufacturer's installation instructions for the specific valve.

Butterfly Valve Questions

What is a butterfly valve used for?

Isolating and regulating the flow of liquids, gases and powders, mainly in medium to large pipe sizes. Typical uses include water and wastewater, HVAC, chemical plants, power stations, food and drink, and bulk powder handling.

Can a butterfly valve be used for flow control?

Yes. A butterfly valve can be held part-open to regulate flow, typically between about 30 and 70 degrees open. With a positioner-equipped actuator it can provide continuous modulating control.

Which way round should a butterfly valve be installed?

Most concentric, rubber-lined butterfly valves are bi-directional and can be installed either way round. Check the manufacturer's instructions for any flow direction marked on the valve.

What is the difference between a wafer and a lug butterfly valve?

A wafer valve is clamped between two flanges by long bolts. A lug valve has threaded lugs so each flange is bolted to the valve separately, allowing the pipe on one side to be removed with the valve still in place.

Do butterfly valves need gaskets?

Rubber-lined butterfly valves do not: the liner seals against the pipe flanges. Fitting extra gaskets can damage the liner and stop the disc sealing.

How long does a butterfly valve last?

With the right seat material and correct installation, a butterfly valve can last many years. Most failures come from a liner that does not suit the fluid or temperature, or from damage during installation.

How quickly can IPT supply a butterfly valve?

Vamein butterfly valves up to DN350 are typically delivered in about 10 days from order and payment. Larger sizes are made to order; ask for a quotation and we will confirm the lead time.