A butterfly valve is a type of valve used to stop, regulate and start the flow in a system. The mechanism of a butterfly valve is similar to that of a multi way ball valve. These two types of valve both applies the quarter turn rotational motion to control the flow. The flow refers to the movement of a medium or the fluid that travels inside a system. Though the butterfly valves and the multi way ball valves share the similar mechanism, they are different in multiple ways.
In order to let the fluid medium passes through the valve, there are ports as the entrance and exit on a valve. Just like the multi way ball valves, a butterfly valve allows fast close and open in an easy manner with a handle. On a conventional butterfly valve, there is a handle to control the open and close. A ninety degree rotation (2 quarter rotation) of the handle gives a complete close or open of the valve ports.
On a multi way ball valve, the quarter rotation is controlled by a crank-like handle which connects to the stem of the control unit of the valve. On a butterfly valve, a hand wheel is used instead of a crank handle to initiate the quarter turns. Sometimes there will be a gearbox between the hand wheel and the stem. The gearbox is used to simplify the rotation operation; yet, the use of it slows down the operation speed at the same time.
The butterfly valve is a type of quarter turn valve just like the multi way ball valves. The basic idea of a quarter turn valve is to control the open and close of the valve by means of the quarter turns. A quarter turn refers to the 90 degree turn of the handle on the valve. By turning the handle the flow of the fluid medium in a system can be regulated. The butterfly valves are used primarily in waste treatment systems.
A butterfly valve works in the way similar to other type of quarter turn valves. They share the same basic components on the device. There are stainless steel valve body, multiple ports on the valves, the stem to control the ports and the handle to turn the stem. The key controlling component on a multi way ball valve is the rotary ball; it is a metal disc that plays the role on a butterfly valve by contrast. The metal disc in the valve gives the name ‘butterfly’ valve.
The butterfly is mounted to stem and when the stem is turned to the close position, the butterfly blocks the flow path of the medium. When the metal disc is moved by a quarter turn, the valve is fully open and the travel of the medium is hence unrestricted. The butterfly disc in the valve can be open and closed both completely and partially. To partially open or close the valve, the handle or the hand wheel is not rotated in a full quarter turn. When the valve is partially open, the flow of the medium is restricted. In other words, only a limited amount of fluid will be allowed through the valve.
Other components on a butterfly valve are to provide the tight seal of the device to prevent the potential leakage. For example, there is a resilient seat on the body of the butterfly valve and there is a packing which serves as another additional seal in case the function of the resilient seat is compromised. The butterfly valves can be operated either manually or electronically. They are commonly applied in an automation system as a result.
The types of butterfly valves are divided by the design of the components on it. For example, there are concentric butterfly valves which have a rubber resilient seat and a metal disc. The double eccentric butterfly valves are the high performance valves which the resilient seat and disc are made from multiple materials. The triple eccentric butterfly valves usually have a laminated seat design which the seat is mostly made from metal materials.
Other than the seat and disc design, the butterfly valves also have different body designs. The wafer butterfly valves feature 2 or more centering holes for installation. The wafer design of the device is lighter in weight and more cost-effective. The wafer butterfly valves are good at maintaining the seal against bi-directional pressure differential to prevent back flow. However, they cannot be used as a pipe end or for end of line services.
The lug butterfly valves have bolt holes to connect with pipe flanges which also offer ease of installation. The butterfly valves in this style are installed between 2 flanges with a separate set of bolts for each flange, which allows either side of the system to be disconnected without affecting the other side. Comparing to the wafer design, the lug butterfly valves are considered safer and they can be used as a pipe end as well as for end of line services.
As for the butterfly valves in larger size, the flanged face design is required. The flanged butterfly valves have a flange face on both sides of the valve. On the other hand, the welded butterfly valves are used for extra high pressure applications. This type of butterfly valve uses metal resilient seat to further guarantee the tight seal when the valve is under high pressure operations.
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