What is a Butterfly valve?
Butterfly valves are quarter-turn rotational motion valves used to stop, regulate, and start flow. Butterfly valves are simple and quick to open. A 90° rotation of the handle closes or opens the valve completely. Large Butterfly valves are typically equipped with a gearbox, which connects the handwheel to the stem via gears. This simplifies valve operation, albeit at the sacrifice of speed.
Parts of the butterfly valve
- Valve Body
- Hand Lever
- Gland Seal
Butterfly valve bodies are typically designed to fit between two pipe flanges. The two most prevalent body types are lug and wafer. Protruding lugs on the lug body offer bolt holes that match those on the pipe flange. A wafer body lacks projecting lugs. The wafer valve is sandwiched between the pipe flanges, and the body is surrounded by flange bolts.
The major feature of butterfly valves is the disc, which allows, regulates, and stops the flow of fluid in the pipeline. The rotating motion of the disc controls the flow. The discharge flow rate is proportional to the degree of disc opening. The fluid is completely prevented from flowing out of the valve when the disc is perpendicular to the flow’s cross-sectional area. Otherwise, the fluid is allowed to circulate through the area between the seat and the disc. A 90o-rotation of the disc from a closed position allows full opening of the valve and vice versa. When the disc is rotated less than 90 o, flow is reduced. Butterfly valve discs are equivalent to ball valve discs and plug valve discs.
The stem of the butterfly valve can be one piece or two pieces (split-stem).
Most resilient seated designs insulate the stem from the media, enabling an efficient material option in terms of cost and mechanical qualities.
The stems in high-performance designs come into contact with the media and must therefore be compatible as well as offer the necessary strength for seating and unseating the disc from the seat.
When the valve is closed, the valve seat is a ring that provides sealing between the disc edge and the valve body. The sealing action is required to prevent any fluid from leaking into the butterfly valve’s outlet. Because the disc moves on the surface of the seat during valve opening, it must be made of a low-friction material.
The butterfly valve seat can be composed of soft or metal material. The butterfly valve’s temperature and pressure ratings are limited by the seat material. Because they distort at higher temperatures, soft chairs composed of plastic and elastomeric materials are confined to lower temperatures.
Pneumatic Cylinders are controlled by hand lever valves. Manually operated valves, such as Hand Lever Valves, are utilised in the absence of an electrical supply.
This gland seal water performs three critical functions: it allows the pump shaft to revolve within its sleeve with minimal friction, it prevents slurry from backing up into the seals and harming the shaft, and It enables some cooling of the pump shaft, which warms up as it turns at high rates.
Advantages and Disadvantages of Butterfly Valves
Advantages of Butterfly Valves
- Pressure decrease is low, and pressure recovery is rapid.
- Throttling characteristics that are satisfactory across the majority of the range
- Because it can clean itself, it can be utilised for slurries.
- Suitable for use with big valves
- It can be utilised with corrosive or chemical media.
- Because butterfly valves are lightweight, they take up less space than globe or gate valves.
- Butterfly valves can be quickly opened and closed.
Disadvantages of Butterfly Valves
- Throttling is only achievable at low differential pressures.
- Cavitation and blocked flow are major challenges.
- The disc’s movement is unguided and influenced by flow turbulence.
- Unbalanced disc torque tends to close the valve.
- Larger valves demand a lot of force to operate the disc.
Applications of Butterfly Valves
- Butterfly valves are suitable for both freshwater and saltwater vacuum services.
- Slurry and comparable services
- Water and steam service at high pressures and temperatures
- It can be used for isolation as well as blocking.
- It can be implemented as regulators in process services where fine control is not required.