Butterfly valve introduction

Butterfly valve is a kind of valve that uses a round butterfly plate as the opening and closing member and rotates with the valve stem to open, close and regulate the fluid passage. There are many types of shut-off valves. They are very common and they are also longest type of valves that we see on pipeline daily. This article introduces you to structural characteristics of shut-off valves and working principle of shut-off valves.

Structure characteristics

The butterfly valve has a simple structure, small size, light weight, and low material consumption. It also has a small installation size and can rapidly switch with a 90° reciprocating rotary motion.It serves for shutting off, connecting and controlling the flow of media in the pipe.

The butterfly valve has good fluid control characteristics and closing sealing performance due to its butterfly plate's streamlined design, which results in minimal fluid resistance loss.

The through-stem structure of the butterfly valve stem has good comprehensive mechanical properties and corrosion resistance, as well as resistance to abrasion after tempering treatment. The valve stem only requires rotary movement for opening and closing, without the need for lifting operation. This ensures a reliable seal by preventing easy damage to the valve stem packing.

Butterfly valves can be connected using flange connection, butt-clamp connection, butt-welding connection, and lug butt-clamp connection. Driving forms include manual, worm gear drive, electric, pneumatic, hydraulic, electro-hydraulic linkage and other actuators. Use them for remote control and automatic operation.

Working principle

A butterfly valve is a valve that uses a circular butterfly plate as the opening and closing mechanism to regulate the flow of media in a pipeline. The valve body contains a cylindrical channel in which a disc-shaped butterfly plate rotates around an axis. The rotation angle can range from 0° to 90°, with the valve being fully open at 90°.

The relationship between the opening of the butterfly valve and the flow rate is generally linear. It is important to note that the improved text has not introduced any new content beyond the original source text. If used to control flow, the flow characteristics of the valve and the piping flow resistance are closely related. For example, if two pipelines have the same valve size and shape but different pipeline loss coefficients, the flow rate difference through the valve will be significant.

If the valve is in the throttling state, the back of the valve plate may experience cavitation, which can damage the valve. This will typically be the case when the valve is more than 15° open.

The valve body and disc create a figure-shaped opening in front of the valve stem when the valve is partially open. This results in two different states on either side of the valve. On one side the disc faces the water flow direction, on the other side it faces the water flow direction and moves accordingly. There are nozzle-shaped openings on one side of the valve body and disc, and throttle-shaped openings on the other side. The flow rate on the nozzle side is faster than on the throttle side. If the flow on the throttling side of the valve falls below a certain value, a vacuum will develop that may cause the rubber seals to loosen.

The operating torque of a butterfly valve varies depending on the direction of opening and closing. For horizontal valves, especially large diameter valves, the torque due to the difference in water depth and valve shaft/head must be taken into account. Additionally, the presence of an elbow device on the valve inlet side can cause bias flow and increase the moment. When the valve is in the middle opening position, the operating mechanism must be self-locking due to the water flow torque.

In the fully open position, the butterfly valve's thickness is the only resistance to the medium flow through the valve body. Therefore, the pressure drop through the valve is minimal, resulting in better flow control characteristics.