A butterfly valve is a device to regulate or interrupt the flow of a fluid in a conduit. The butterfly valve allows the passage section to be increased or reduced by means of a plate that rotates on an axis. This plate is called a butterfly. By reducing the fluid passage area, the local pressure drop in the valve increases, reducing fluid flow.
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 pitch area and the throttle's turning angle is not linear.
Butterfly valves are used in air ducts, pipes for liquids and in mechanical applications, such as in some types of heat engines.
What advantages and disadvantages do butterfly valves have?
Butterfly valves, like ball valves, are one of the most modern and progressive valve types, which has many important advantages, including:
- They are mechanisms of small construction length and weight;
- Simplicity of design, with a small number of parts;
- 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-seated seal, but modern valves with metal-to-metal lamellar seals also have a tightness class "A", even when tested with gas.
What are the types of butterfly valves?
There are 4 different types of butterfly valves:
Butterfly
swivel type- Double Eccentric Butterfly Valve (2 Eccentric)
- 3 Way Eccentric Butterfly Valve
- 4 Way Eccentric Butterfly Valve
Butterfly Valve Design Differences
The shutter (the movable part of the blocking member) of these devices can be a flat disc or a section of biconvex lenses (lenses).
The design of butterfly valves allows their use in various working environments, providing protection against corrosion and increased wear on the internal surfaces of the casing and disc, for which various methods are used.
The simplest of these is the manufacture of these parts from stainless steels with a rubber ring seal (if protection is not 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 casing and rubber or polymer. disc covers, which replaces additional gaskets.
The connection of the valve to the pipeline is most often tightened, that is, the holes on the edge of the valve body penetrate the bolts from one pipeline flange to another, which is ideal for the design of the device, in cases In rare cases, the valves are made with their own flanges for connection to the return pipe flanges.
The control of butterfly valves is similar to the control of 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 or (for large diameters) multi-turn electric drives, 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 with low pressures.