Butterfly Valve Seat Selection Guide

Main types of butterfly valves

There are two broad families of butterfly valves. Briefly, the difference is whether the stem is concentric with the centerline of the valve body or eccentric or slightly off-centre in two or three planes. This geometric difference is responsible for the differences in the way that various butterfly valves seat and shut off. These two groups overlap somewhat in rating and performance, but in the operational characteristics that really matter, such as pressure rating and shut-off ability, these two types of valve are quite different. Needless to say, because the two valves look quite alike (that is, they both are often very short face-to-face and often do not have separate flanges of their own, and they both have a disc that turns inside the pipe) and they share the butterfly valves name, they are often confused.

Both valves have certain characteristics that make them worthy of choice over, for instance, a gate valve. But both have certain very definite shortcomings, and not the same shortcomings for each type. To illustrate the point that confusion between these two has been rampant, a company that was one of the pioneers in the high-performance butterfly valves market spent 10 years and many advertising dollars trying to get their valve referred to as something other than a "butterfly" valve. They tried referring to it as a "trunnion" valve, which is an apt name but not very distinctive. They tried referring to it as an "eccentric disc" valve, which is more descriptive but longer. Other manufacturers put forth their own nomenclature, as well as a sizeable amount of effort to demonstrate the difference between the two valves, and sometimes the similarities, depending on their strategy at the time. At the time of this writing, it appears that the name "high-performance butterfly valve" is almost universally used for these valves. The other branch of the family is not "low-performance" but is generally referred to as "rubber lined" or "concentric" butterfly valves. Some of these, especially the ones that are not actually rubber lined, are quite special valves in their own right.

For the safety and efficiency of a variety of processes, we rely on the performance of butterfly valves. How sound a butterfly valve is depends on the integrity of the seal.

The valve must be able to withstand the particular working conditions of any given process. Such conditions involve elements that are corrosive, extremely hot, or high pressure. The seal must resist wear and tear with repetitive opening and closing.

The integrity of the seal depends on the butterfly valves seat. That’s why you must choose one that is appropriate for the conditions of the process. With this guide, you will learn which butterfly valve seat is suited for which process.

What is a Seat On a Valve?

Essentially, a valve seat is where the moving component of a valve rests when in the closed position. In butterfly valves applications, the disc rests securely on the seat to close and seal the valve. Seats are designed to keep the seal intact despite the thermal, friction, and impact stresses of a process.

Selecting a Valve Seat Type

We have different types of butterfly valves for various applications. The type of butterfly valve seal used depends on the application conditions: temperature, pressure, and type of media. For more information on what pressure and temperature a valve can tolerate, refer to the specs published by the manufacturer.

BUNA-N (B)

BUNA-N is another name for nitrile which is a synthetic rubber copolymer of acrylonitrile (ACN) and butadiene. Because of its abrasion resistance, tensile strength, and low compression set, this rubber is a widely used elastomer in the seal industry.

BUNA-N is highly resistant to hydraulic fluids, water, alcohols, acids, petroleum-based oils, fuels, silicone greases, etc. However, what makes it strong also makes it inflexible. BUNA temperature rating is 0°F to 180°F and is heat resistant up to 225°F.

This material is used in some automotive applications. However, BUNA-N is not suitable for applications that involve acetones, ketones, chlorinated hydrocarbons, nitro hydrocarbons, or ozone.

EPDM (E)

EPDM stands for Ethylene Propylene Diene Monomer and is alternatively called EPT, Nordel, or EPR. This elastomer stands up to abrasives such as acids and alkalines. It is also tear-resistant and stands up to weather elements and ozone.

EPDM is ideal for processes that involve water, alcohols, bleach, glycols, ketones, phosphate, esters, chlorine, and other alkaline solutions. EPDM temperature rating range is -30ºF to 225ºF.

EPDM is widely used in HVAC systems. However, EPDM is not suitable for applications that involve lines with compressed air containing petroleum-based oils, hydrocarbon solvents or oils, chlorinated hydrocarbons, turpentine, etc.

PTFE (P)

PTFE is an abbreviation of the term polytetrafluoroethylene and is commonly kno

wn as Teflon. This thermoplastic fluoropolymer has low friction, chemical resistance, and fire-resistant qualities. Teflon is used to create some resilient seated butterfly valves.

PTFE is a cost-effective material in applications such as chemical processing or oil and gas. Because of its insulation quality, it is compatible with electrical applications. However, it should not be used in high-pressure conditions. PTFE temperature rating ranges from -50°F to 400°F.

VITON (V)

VITON is a registered trademark name for a fluorocarbon elastomer made by Dupont. 3M’s version of this material is known as Flourel. This elastomer offers heat and chemical resistance.

VITON is resistant to mineral acids and hydrocarbon products that are either concentrated or diluted. VITON temperature rating ranges from -20°F to 300°F.

Fluorocarbon is used in applications that involve petroleum oils, chlorinated hydrocarbons, salt solutions, and mineral acids. Because of its heat tolerance and resistance to corrosion, VITON is used in the manufacture of valve seats such as a knife gate valve. However, this valve is not compatible with processes that involve water or steam.