What is Butterfly Valve?
Butterfly valve is a quarter turn (90 degrees) rotational motion valves used as throttling valves to regulate flow through a system, which has a circular disc or plate of the same radial measurements as the pipe is pivoted exactly in the middle of the pipe, vertical to the direction of the flow. The disc of the butterfly valve is connected to an actuator outer side of the valve by means of a rod. The valve disc or plate when turned in the center and moved by means of an actuator, develop an illustration of the butterfly wings and hence they are renowned as butterfly valves.
How butterfly valve works?
A butterfly valve embraces a circular disc that is built with a stem through the middle or attached offset, so as when the valve open, the disc pivots 90 degrees in the valve bore, supporting with the flow and thus creating an almost unobstructed flow path. The operation of the butterfly valves is largely similar to the ball valve and permit for quick shut off.
In the fully closed position, this disc blocks the line completely, whilst in the fully opened position, this disc is at a right angle to the flow of the respective media (liquid, gas, air). These butterfly valves are known for effectively stop, regulate and start the flow of the respective media (liquid, gas, air) and for the same it has gained an immense popularity in the market.
In simpler language, butterfly valve can open or close whenever the disc turned 90 degrees and for this property is extensively used to control the flow of liquids through a section of pipe.
It requires a number of components to construct the butterfly valve incorporating body, disk, stem and seat; however the imperative one is an apparently metal disc.
Butterfly Valve Body:
The body of the butterfly valve fit between two pipe flanges, and therefore lug and wafer body designs are widely used one in the industries.
Butterfly Valve Disk:
This metal disk is also reckoned as a butterfly, and is the primary component of the butterfly valve. This butterfly valve is equivalent to a plug in plug valve, ball in a ball valve and gate in a gate valve. When the valve is closed, the disc blocks entrance of fluid, whilst full open, the disc moves a quarter turn and permit fluid, air of gas to pass. Moreover, the disc is also used to permit the specified amount of flow, in which the valve is partially open. That means the disc will neither be open nor close, and thus it provides smaller passage only to pass smaller amounts of fluid, air or gas through.
Butterfly Valve Stem:
The one piece shaft or two piece shaft, used in the butterfly valve is renowned as a stem, a stem that is protected from the media in all resilient seated configurations of the butterfly valve, and hence it is recommended to select the material wisely for your application requirement.
Butterfly Valve Seat:
The valve seat is known to be used between the disk edge and body to deliver specific shutoff, wherein the seat is made of the variety of elastomers or polymers and largely find bonded to the body.
Other than, there are several secondary components that can be used with the butterfly valves incorporate resilient seat, body, packing, a stem and an actuator as per application requirements. Further, the actuator connected to the valve can be equipped with an automatic mechanism or remote control mechanism for controlling the flow of the liquid automatically. For the manual control of the actuator, it is attached to a lever.
Owing to the popularity, this butterfly is available in the different types, wherein each shares exclusive configuration and application. Below is the classification of the butterfly based on the orientation of the stem to the disc and the seating angle that the disc closes on.
Concentric Butterfly Valve:
This is a very common configuration which is also famous as a resilient seated butterfly valve in the industries, wherein the stem (shaft) is placed in the middle of the valve disc, which is centered in the pipe bore. This type of valve holds the rubber seat and depends on the disc having a considerable level of contact with the seat to strength the seal, wherein the disc contacts the seat most primitively during the 90 degree rotation.
Single Offset Butterfly Valve:
In this type of butterfly valve, the stem (shaft) is placed at the back of the disc, wherein the single offset of the shaft causes the disc to contact the seat, but this time there is a distance of three to four degrees between disc and seat to accomplish longer lifespan.
Double Offset Butterfly Valve:
This type of butterfly valve is also celebrated in the industries as the high performance butterfly valve having a disc with two offsets. Just like a single offset configuration, these valves also have stem behind the disc, whereas the second offset stem is moved once more off the center of the disc to one side. The ingenious design of this type of butterfly valves enables high performance unfailingly and hence is one of the favorites in the industries where higher pressure resistance is essential.
The both single and double offset butterfly valves are known to be versatile and can be operated by means of handles, gears, or actuators. All these devices are connected with the stem move the valve disc to the maximum position for absolute close or open the valve. This finds huge application in the water, petrochemical and chemical industries, whereas used in power and fuel handling systems too.
Triple Offset Butterfly Valve:
This type of butterfly valve is just like a double offset valve, wherein the stem is placed back of the disc and offset to a side of double offset. The third offset of this triple offset butterfly valve and seating surface develops a cone shape of the disc, which wedges into the seat with very negligible contact between the sealing surfaces until closed completely. The reduced contact with the seat with a disc delivers effective sealing as well as longer life to the valve.
- The speed at which butterfly valve can perform a quarter turn open/close operation, no other valve can.
- The flow control butterfly valve shares for an extensive range of liquids, gases, suspended oils and slurries, no other valve can.
- The compact design, light weight construction and its available in a variety of material is what makes the butterfly valve preferred choice in the market.
- The compact design requires less space, unlikely to globe, gate, ball and other analogous valves.
- The material used in the construction shares high strength to low weight ratio, hence is light in weight facilitates easy installation
- The valve completely opens in just a quarter turn (90˚), hence it requires less time to open or close
- The wide variety of the specification is available ranging from DN 40 (NPS 1½) to over DN 5000 (NPS 200)
- Every single valve shares low pressure drop and high pressure recovery
- Precision machining of the enabling bubble tight shut off that no other valve can guarantee
- The less moving parts in conjunction with no pocket areas prevent fluids trapping and hence require no maintenance virtually