Butterfly Valves: A Complete Overview for Engineers and Procurement Professionals

When it comes to controlling large flows in pipelines, few valves can match the butterfly valve for a combination of simplicity, space efficiency, and cost-effectiveness. Used extensively in water treatment, HVAC, fire protection, and chemical processing, butterfly valves are a staple of flow control engineering. Yet choosing the right one requires a good understanding of the different designs, materials, and limitations available on the market.

At Valves UK, we supply butterfly valves to a wide range of industries across the UK, and in this guide we'll give you a thorough technical overview to help you specify the right product with confidence.

How a Butterfly Valve Works

The butterfly valve gets its name from the wing-like action of its disc, which rotates around a central shaft. When the disc is parallel to the flow, the valve is fully open and offers very low resistance. When rotated 90 degrees so the disc is perpendicular to the flow, the valve is fully closed. The operating mechanism is simple: a quarter-turn of the stem — whether by hand lever, gear operator, or actuator — opens or closes the valve. This quarter-turn operation makes butterfly valves fast to operate and easy to automate, which is why they are so commonly paired with pneumatic or electric actuators.

Types of Butterfly Valves

Concentric (Resilient Seated) Butterfly Valves: This is the most basic and affordable design. The disc is centred in the bore and the shaft passes through the centre of the disc. The seat is a rubber or elastomeric liner inside the body, and sealing is achieved by the disc pressing against this seat. These valves are suitable for low-pressure applications (up to PN16) and work well with water, neutral liquids, and compressed air. They are not suitable for steam or highly corrosive media.

Eccentric (High Performance) Butterfly Valves: The shaft is offset from the centre of the disc in one or more planes. Double eccentric (double offset) designs reduce wear and improve sealing. Triple offset butterfly valves achieve metal-to-metal sealing and are suitable for high-pressure, high-temperature applications including steam and corrosive chemicals.

Body, Disc, and Seat Materials

Body materials include ductile iron or cast iron (common for water and general service), carbon steel (for oil, gas, and petrochemical applications), stainless steel 316 (for corrosive media, food-grade, and hygienic applications), and PVC or PP (for chemical handling and water treatment with aggressive media).

The seat (liner) material is critical to the valve's performance and must be compatible with the media, pressure, and temperature. EPDM is suitable for water, steam up to approximately 130°C, and many chemicals. NBR (Nitrile) is good for oil and petroleum-based fluids. PTFE offers excellent chemical resistance, is food-safe, and is suitable for higher temperatures. Metal stainless steel seats are used for high-temperature and high-pressure applications in triple offset designs.

Wafer, Lug, and Flanged Styles

Butterfly valves are available in three main end connection styles. Wafer style valves are sandwiched between two pipe flanges using through bolts — lower cost but cannot be used as an end-of-line valve. Lug style valves have threaded inserts (lugs) around the body, allowing the valve to be bolted to a single flange on either side and are suitable for end-of-line or dead-end service. Flanged valves have full flanges on both ends, making installation and removal easier and more robust.

Actuating Butterfly Valves

Butterfly valves pair exceptionally well with pneumatic and electric actuators. The quarter-turn operation aligns perfectly with the output of most actuators, and the ISO 5211 mounting pad found on most butterfly valves ensures compatibility with standard actuator mounting kits. At Valves UK, we can supply butterfly valves pre-assembled with Air Torque or Koei actuators, complete with bracket and coupling (AP kit), ready to install.

Common Applications

Butterfly valves are widely used in water treatment and distribution, HVAC and building services (chiller systems, cooling towers), fire protection systems, chemical and pharmaceutical processing, food and beverage production (with PTFE/EPDM seats and stainless steel body), and power generation (cooling water, fuel lines).

Conclusion

Butterfly valves offer a compelling combination of simplicity, low maintenance, space efficiency, and cost effectiveness. Whether you need a basic wafer-style butterfly for a water treatment application or a high-performance triple offset design for a high-pressure steam line, getting the specification right is key. The team at Valves UK is here to help — browse our range online or speak to one of our technical specialists today.