1. What is butterfly valve? Butterfly valve, English name is Butterfly valve, shortened to butterfly valve or butterfly valve, is an industrial valve used to regulate (open / close) the flow in pipelines with many different sizes. Due to its structure, it looks like a butterfly, so it is called  butterfly valve for short. The valve opens/closes the fluid thanks to the disc element that can rotate around the shaft at different angles. Normally butterfly valves are controlled by levers, cranks or electrical or pneumatic actuators. Along with gate valve, knife valve, ball valve, butterfly valve is one of the types of quick-closing / quick-opening valves. Butterfly valve has a simple, compact structure, and especially the cost to buy this valve is lower than other industrial valves with the same function.

2. Structure & working principle of butterfly valve

a. Structure of butterfly valve:

Butterfly valves have a fairly simple structure compared to other valves, including the following basic parts:

- Body:  The body of the valve is usually a round metal (or plastic) block, molded in one piece, designed with holes to catch bolts, fixed to the flange. The position of the bolt holes is determined by the standard of the flange (some common standards such as BS, ANSI, JIS, ...).

- Valve shaft (Stem):  It is a direct link between the valve arm and the valve disc, directly deciding the opening/closing stroke of the valve. The valve shaft will transmit torque from the handwheel to the valve disc, helping the valve disc rotate in the direction of the handwheel to open/close. The valve shaft is usually made from hard metal, resistant to corrosion and good friction, because it bears a lot of force.

- Valve disc (Disc):  Also known as vane, usually has a round shape, located between the valve body and in direct contact with the medium, so it is usually made from materials with high hardness & good corrosion resistance. The valve disc is usually fixed directly to the valve shaft linked to the handwheel, thereby opening / closing according to the stroke of the valve arm.

- Sealing gasket (Seat):  As a sealing part, which determines the tightness of the valve, usually made of materials such as synthetic rubber, teflon, PDFE, etc. between valve disc & valve body

- Valve arm:  A part that receives force directly from the user to operate the valve opening/closing. Butterfly valves are usually used with a lever operating handle. From the lever (or handwheel through the control gearbox for large sizes), through the valve shaft to control the valve disc according to the desired stroke, thereby allowing/preventing the fluid to flow through the valve.

b. Working principle of butterfly valve:

When turning the valve handle in an anti-clockwise direction, the butterfly valve opening process is performed and vice versa. Through the force acting on the valve arm, it transmits torque to the valve shaft and controls the valve disc to open/close. When the valve is 100% fully open, the disc will lie parallel to the direction of flow & pipeline, and when the valve is fully closed, the valve disc will lie perpendicular to the pipeline. Note that butterfly valves are best used when fully open or closed, not effective when used to regulate flow. Butterfly valves are fragile when opened to regulate flow at an angle of 15°C - 75°C.

3. Butterfly valve classification:

Depending on the classification criteria, we can classify butterfly valves into many different types. Here are some common criteria used to classify butterfly valves:

a. Based on connection type:

- Clamp butterfly valve:  The clamp butterfly valve, whose English name is Wafer Butterfly Valve, is the most common type of butterfly valve, with a simple structure and the cheapest price. This type of valve has a connection part consisting of only 02 or 04 positions to connect bolts to the flange at the top & bottom of the valve body, the rest is sealed by pressing & tightening bolts between the two sides. flange of the pipe.

- Flange butterfly valve:  Butterfly valve has the English name Lug Butterfly Valve, is a valve designed with full bolt positions associated with the flange of the pipeline. This makes the valve withstand higher pressures, ensuring better valve tightness.

- Double Flange Butterfly Valve:   Double Flange Butterfly Valve, English name is Double Flange Butterfly Valve, is designed with two separate flanges to catch with two flanges of the pipeline. With this design, this butterfly valve is used in high pressure conditions, large pipe sizes, or some special working conditions for small pipelines.

b. Based on the mode of operation:

- Hand lever butterfly valve:  Also known as clamping butterfly valve or duckbill butterfly valve, this is the simplest type of butterfly valve, the most commonly used today. The valve arm is opened when using clamping force, after adjusting the valve disc position, release the valve handle to lock it. When adjusting the position of the valve arm, the valve arm will open and close like a duck's beak. The valve is opened or closed, or the flow is regulated by turning the lever around the axis of the butterfly valve. This type of valve is usually applied to small sizes because the operation of the lever is relatively difficult.

- Handwheel butterfly valve:  This type of valve is also manually operated, but mostly for large sized valves, or high pipeline pressure. The valve is equipped with an attached gearbox, making it easier for users to operate.

- Electric control butterfly valve: This is an automatic butterfly valve line, the valve is equipped with an electric control actuator. This type of valve usually has a opening and closing time of 10-15s to 60s (or more), is mainly used for large pipelines, using clamps or gearboxes is not feasible, or in environments that are difficult to manipulate, operate, and dangerous for users.

- Pneumatically controlled butterfly valve:  Like an electrically controlled butterfly valve, this type is also equipped with an actuator but runs on compressed air. The valve is controlled to open/close the stroke through a pneumatic controller, making the opening/closing process fast, low cost & durable, but it requires a compressed air supply. Pneumatic control butterfly valve is more and more widely used in many different fields.

4. Pros & cons of using butterfly valves:

a. Advantages:

- Butterfly valve has a small, compact design, easy to operate & use.

Butterfly valves are suitable for many installation locations due to their much smaller dimensions compared to other types of valves.

- Has a simple structure, so the process of maintenance, repair or replacement is also simple.

- The cost can be considered as the lowest among industrial valves.

- Can be installed simultaneously for many different standards on the same valve (especially Wafer type). For example, the same Wafer butterfly valve can be installed to ANSI, JIS, BS, etc.

b. Defect:

- Even when closed or open, the control valve affects the flow rate & flow because the valve disc is always above the flow.

- Butterfly valve size is limited to small sizes, usually only from size DN40 and above. Some new types of microbiological butterfly valves have sizes DN10, DN15.

- It is very difficult to manufacture butterfly valves for special environments. Especially when the temperature is high from 300 degrees Celsius or more, the pressure is 25 bar or more….

- The durability of butterfly valve is not high compared to other valve lines.

- Butterfly valve is only used mainly for opening / closing purposes, not suitable for flow regulation purposes, because when operating, the valve disc is always in the flow. If used for the purpose of regulating flow, the service life of the valve will be significantly reduced.

The above article is summed up by us during our research and practical work. However, there may still be shortcomings because each individual's views and judgments are different, we hope for your understanding & suggestions.