Butterfly valves are quarter-turn valves which are easy and quick to open by rotating the operator by 90°. The butterfly valve is a popular choice because it can be easily opened and closed by hand. Their advantage over ball valves is that they are easy to open, and they do not require special training or tools to operate. This makes them ideal for emergency situations when the operator may not have time or access to use a standard hand-operated valve.
Types of Butterfly Valves
There are two types of butterfly valves, concentric (rubber lined) and eccentric type. Eccentric will be either double or triple offset valves. The choice of a butterfly valve (concentric, double offset and triple offset) is dependent on the application and operating condition required.
- Concentric Butterfly Valves
The concentric type is a general use butterfly valve with the shaft located in the centre of the disc. The disc makes contact with the seat during the opening or closing of the valve and as a result, gives a bubble-tight shut off. Soft seated butterfly valves are suitable for low pressure and non-critical applications up to approx. 20 bar.
- Double Offset Butterfly Valves
The double offset butterfly valve has 2 offsets. The first offset is the shaft from the centreline of the disc and body. The second offset is from the centreline of the bore. The double offset butterfly valve is also known as a high-performance butterfly valve. This design is suitable for high temperature and pressure applications for on-off or throttling services.
- Triple Offset Butterfly Valves
The triple offset butterfly valve has 3 offsets. The first two offsets are the same as the double offset with the third offset achieved by altering the geometry of the sealing component. The third offset eliminates rubbing and reduces wear between the seat and seal during operation and creates a bi-directional bubble tight seal. The metal seated Triple design allows the valve to be used in a high temperature and high-pressure environment with a much longer lifetime than double offset.