A butterfly valve is a device for regulating or interrupting the flow of a fluid in a conduit. The butterfly valve allows to increase or decrease the passage section by means of a plate that rotates on an axis. This plate is called a butterfly. By decreasing the area of passage of the fluid, the loss of local pressure in the valve increases, reducing the flow of the fluid.
Butterfly valves can be distinguished in the field of hydraulics according to the following characteristics:
- They are in all cases contained inside the pipe;
- They have a low pressure drop when fully open.
- The relationship between the area of passage and the angle of rotation of the butterfly is not linear.
Butterfly valves are used in air ducts, liquid lines, and in mechanical applications, such as some types of heat engines.
What are the advantages and disadvantages of butterfly valves?
Butterfly valves, like ball valves, are one of the most modern and progressive valve types, having many important advantages, including:
- They are mechanisms of small length and weight construction;
- Simplicity of design, with a small number of pieces;
- Relative ease of repair, the ability to quickly replace sealing elements;
- Possibility of application for large pipe diameters.
But there are also disadvantages, for example:
- In the "open" position, the disc is located in the fluid path, which degrades the hydraulic characteristics and makes it difficult to clean the pipe with mechanical devices.
- Relatively small (for ball valves and gate valves times more) of torque control gates;
Leakage class "A" is achieved not only in valves with a soft seat seal, but modern valves with metal-to-metal lamellar seals also have a "A" seal class, even when tested with gas.
What are the types of butterfly valves?
There are 4 different types of butterfly valves:
- Double Eccentric Butterfly Valve (2 Eccentric)
- 3 way eccentric butterfly valve
- Eccentric 4-way butterfly valve
Butterfly Valve Design Differences
The shutter (the movable part of the locking member) of these devices can be a flat disk or a section of biconvex lentils (lenses).
The design of the butterfly valves allows their use in various working media, providing protection against corrosion and increased wear on the internal surfaces of the housing and the disc, for which various methods are used.
The simplest of them is the manufacture of these parts from stainless steels with a rubber ring seal (if no protection is required, the parts are made of carbon or alloy steel, the body is also made of cast iron ). There are also designs whose internal cavities are protected by chemical and wear resistant coatings in the form of elastomeric or rubber inserts in the housing and rubber or polymer. disc covers, which replace additional gaskets.
The valve connection to the pipeline is tightened more frequently, that is, the holes in the edge of the valve body penetrate the bolts from one pipe flange to another, which is ideal for device design, in cases Exceptional valves are made with their own flanges for connection to the pipeline return flanges.
The control of the butterfly valves is similar to the control of the ball valves, since these types of valves require 90 ° for a complete opening of the blocking element. It is carried out manually (in large diameters with flywheel and gearbox) or mechanically, using single-turn electric drives or (for large diameters) multi-turn, as well as pneumatic and hydraulic piston drives.
A variety of butterfly valves are hermetic valves used for installation in small diameter pipes for small pressures and in ducts, also at low pressures.