What is a butterfly valve and what is it used for?

Butterfly valves have grown in popularity over the years due in so small part to a compact and lightweight profile that makes the initial cost outlay for these valves significantly lower compared to other valve designs. In this article, PIF explains how butterfly valves function, their pros and cons, and typical applications.

What is a butterfly valve?

Butterfly valves are relatively simple shut-off valves. Needing just a quarter turn of an inbuilt disc to fully open or close, butterfly valves offer quick opening and closing. Suitable for a vast array of applications – such as water supply, wastewater treatment and gas supply – butterfly valves are famed for being compact, lightweight and cost-effective compared to other types of valve.

Butterfly valve types

There is an array of different butterfly valve types, each with their own unique features and benefits. They are defined by the orientation of the stem to the disc and the seating angle that the disc closes on. The most basic version is known as a concentric or resilient-seated butterfly valve. With this design the stem is centred in the middle of the valve disc, exerting a high degree of contact with the rubber seal to effect a seal.

Rare single-offset butterfly valves have latterly been superseded by high performance or double-offset valves. These valves feature a stem behind the disc, with the second offset’s stem positioned off centre to the disc. This geometry means that the 90° disc rotation only rubs over the seat for one to three degrees of its rotation, thus increasing sealing ability and reducing wear to the valve. Handles, gears or actuators can be used to operate both resilient and offset butterfly valves.

Finally, the triple-offset butterfly valve (TOV or TOBV) is a heavy-duty valve predominantly used in harsh conditions. TOVs are similar in construction to double-offset valves, except they are typically metal-seated and feature a third offset – the geometry of the seating surface. This creates a cone-shape of the disc and seat that wedges into the seat with minimal contact between the sealing surfaces until fully closed. This makes sealing more efficient and extends the life of the valve.

Butterfly valve advantages and disadvantages

In a direct comparison with similarly specified globe valves, butterfly valves generally offer more advantages. However, they do fall short in several areas.

Advantages:

• Butterfly valves are more compact and lighter.
• Butterfly valves are less expensive.
• Butterfly valves have fewer parts and are easier to maintain.
• Butterfly valves are available in sizes up to 20 inches.
• Butterfly valves deliver bubble-tight, leak-free closure.
• Butterfly valves can provide accurate, stable, modulating flow control.

Disadvantages:

• Butterfly valves have a greater potential for water hammer.
• Butterfly valves are typically not as well understood.

Butterfly valve applications

Butterfly valves are used across a wide range of applications, particularly in large volume water applications. They are commonly found in the water, chemical and petrochemical industries, as well the following types of applications: vacuum service; fuel handling systems; oil and gas applications; compressed air or gas applications; slurry and similar services; cooling water, air, gases, fire protection; and high pressure/temperature water and steam services.