Types of Butterfly Valves

Types of Butterfly Valves. A butterfly valve has a circular disk approximately the size of the orifice of the pipe diameter. 

Butterfly Valve

This disc rotates around its center so that when closed, the disc fully covers and seals the inner diameter of the pipe. 

When fully open, the disc thickness is along the center of the pipe. 

Fluid flows across both sides of the disc.

The butterfly valve has the advantage of a 90° closing operation and does not accumulate fluids such as the ball valve and plug valve. 

Some of their main advantages in comparison with other valve families are their simple construction and compactness, as a result, finished products are lighter and cheaper, with lower installation footprints and faster operating speeds

Butterfly Valve Parts

The primary components of the butterfly valve are:

• Valve Body
• The valve body fits between the pipe flanges – the most common types of end connections are flange, dual lug and wafer.
• Disc
• Attached to the valve body is the disc that functions as a gate that stops or throttles fluid flow. 
• The disc is usually drilled to fit the stem, or shaft. There are many variations in disc design, orientation and material to improve flow, sealing and/or working torque. 
• Seat
• The inner valve body is covered with a solid elastomer, or metal seal that holds the disk in place in the closed position for a complete shutdown. 
• Stem
• The valve shaft, often referred to as the stem, is the component that connects the disc to the actuating mechanism and transmits the torque through it.
• Seals
• Seals are present at multiple interfaces within the valve to either ensure a tight seal during operation, or to isolate the process media from the valve’s internal components for a more flexible and cost-efficient design.

Butterfly Valve Types

There are two types of butterfly valves:

The concentric type.
The eccentric type.
The eccentric type can be single, double, or triple-offset type.
While it is possible to have a single offset butterfly valve, it is rarely found on the market.
The most available in the market for an eccentric type is double-offset or triple-offset.
At times, this 2 butterfly valve subtype is also called a high performance butterfly valve. With these 3 variants of butterfly valve (concentric, double offset and triple offset)

Concentric, double-offset, and triple-offset butterfly valve

Concentric Butterfly Valves

The concentric butterfly valve is a standard or a general use butterfly valve. The shaft is centrally located on the disk. During opening or closing, there are certain parts of the disk that are still in contact or rubbing the seat. This arrangement will experience friction of the seat whenever the valve works. In a typical application, this concentric butterfly valve is limited to, class 150 because of the seat design.

Double-offset Butterfly Valves

The double offset butterfly valve (also called High Performance Butterfly Valve) is a valve which has 2 offset to the concentric butterfly valve. The first shift is the shaft located not at the center of the disk, but slightly behind the disk.
This displacement will make the valve has a continuous sealing surface of the disk.

The second offset is the shaft located not in the pipe centerline, but located on slightly in the right side of the center.
This offset will prevent the valve from touching the seat at all when fully open.
This arrangement will make the seat experience less friction than the concentric type butterfly valve and thus prolong its service life. In a typical application, this double-offset butterfly valve is limited to class 600 only.

Triple-offset Butterfly Valves

The triple offset butterfly valve is a valve that has 3 offset compared to the concentric butterfly valve.
Just like the double-offset butterfly valve that has 2 offsets, this triple offset also has the same offset, except that it has an additional offset which is a conical shaped seat.
This cone shaped seat will match the disc, which was also manufactured to match the seat. This arrangement will make the seat has no rubbing while closing or opening.
This arrangement will also make the valve has a bubble-tight in a high-pressure application and much longer service life rather than a dual-offset butterfly valve. In a typical application, similar to the double offset butterfly valve, this triple offset butterfly valve is limited to class 600 only.

The figure shows the arrangement of the Concentric, Double-offset, and Triple-offset Butterfly Valves

Body Types of Butterfly Valves

There are 4 main body types: Wafer, Lug, Flanged, and Welded.

Wafer

Contains at least two centering holes to facilitate installation.
Is lighter and cheaper.
Not suitable for use as a pipe end or end service.

Lug

Has bolt holes to connect with pipe flanges.
Because it has threaded bolts around the entire area, the lug valve is a safer option—most customers can switch between a waffle valve and a lug valve, however, they cannot switch from a lug to a wafer.
The lug valves, can be used as a pipe end or as an end-of-line service.
With some lower-strength body materials, the lug threads are weak; therefore, lug valves may have lower bolt torque ratings than a wafer.

Flanged

Has a flange face on both sides of the valve.
It is popular in very large valves.

Welded

Used for extremely high pressure applications.

Butterfly valves are especially well-suited for the handling of large flows of liquids or gases at relatively low pressures and for the handling of slurries or liquids with large amounts of suspended solids.

Assembly of the butterfly valve – Types of Butterfly Valves

The position of the valves in the piping system should be considered. The valve must not be located too close to other valves, elbows, etc.,  because its performance and torque requirements can be impacted.
It is recommended that the valve has at least six upstream pipe diameters and four downstream pipe diameters between it and other valves, elbows, etc., in the piping system. 

The high performance butterfly valve can be mounted in the pipe with the shaft in vertical, horizontal or other diagonal position, depending on the application.
However, in media with concentrations of solid or abrasive particles or media subject to solidification buildup, the performance and lifetime of the valve will be improved by mounting the valve with the shaft in the horizontal position. 

Typical uses of Butterfly valves

A butterfly valve can be used in many different fluid services and they work fine in slurry applications.
Here are a few typical applications for butterfly valves:

• Cooling water, air, gas, fire protection and so on.
• Slurries and similar services.
• Vacuum service
• High pressure and high temperature water and steam utilities.

Advantages and Disadvantages of using a Butterfly Valve

Advantages

• The compact design requires much less space in comparison with other valves.
• Light-weight.
• Fast operation requires fewer opening and closing times.
• Available in great sizes.
• In the higher sizes, >2″ (DN50), butterfly valves are lighter, smaller, and cheaper than competing Globe, Gate, Ball, and Plug valves.

Disadvantages

• Butterfly valves do not allow pipe scraping. The scraping of a pipeline happens when you send a device through the pipe for cleaning.
• The disc will reduce the amount of stream that passes through the pipe. Other types of valves (Ball, Gate, etc.) do not have this issue.
• Cavitation and obstructed discharge are two potential concerns.
• The movement of the disk is not guided and is affected by the turbulence of the stream.

See the following publication for a useful article on membrane valve types.

Types of Butterfly Valves – Calculate Man Hours