A butterfly valve is a device for interrupting or regulating the flow of a fluid in a conduit, increasing or reducing the passage section by means of a plate, called a "butterfly", which rotates on an axis. By decreasing the passage area, the local pressure loss in the valve increases, reducing the flow.

Characteristics of butterfly valves

These valves are low pressure (125 lbs) and simple design, usually used to control the flow and regulate it although it is not completely recommended. They are characterized by being of fast operation, since it only needs a quarter turn to move from the closed position to the open position, also having a small pressure drop since they do not alter the direction of the fluid.

There are wafer or wafer type butterfly valves, lug type or ears and flanges in sizes from 24 ”, being the most common for its ease of installation waffer type butterfly valves. The butterfly valves are suitable for installation in tight spaces or where the process line cannot support much weight.

The fundamental parts of a butterfly valve are the body that can be made of iron, carbon steel, stainless steel, pvc, cpvc or other plastic; the disc that integrates the same materials of the body and the seat that may be mainly made of elastomers such as EPDM or buna having other additional materials depending on the application of the valve. They can be used in handling clean water or with solids up to a certain%, it can also be used for corrosives such as acids and many other fluids depending on the pressure and temperature that is handled in the process line.

The butterfly valves can be operated with lever, gear operator or pneumatic or electric actuators.

There are also high-performance butterfly valves which withstand higher pressure and temperatures and more severe operating conditions. These valves cause small pressure losses, both as if they were in a half-open position, as well as completely open. However, in closed position they do not always get a tight seal. In this regard, good results are obtained if the closure is achieved by pressing the disc on an inner lining of Buna N.

Advantages and disadvantages of butterfly valves


Advantage
  • Light weight, compact, low cost.
  • It requires little maintenance.
  • Minimum number of moving parts.
  • It has no balls or cavities.
  • High capacity.
  • Straight line circulation.
  • It cleans itself.

Disadvantages
  • High torque (torque) to drive it.
  • Limited capacity for pressure drop.
  • Prone to cavitation.