Butterfly Valve Working Principle And Flow Characteristics

Lined Butterfly Valve Working principle:

Butterfly valve is a kind of valve that uses a circular butterfly plate as the opening and closing part, rotates around the valve shaft to open, close and adjust the fluid channel. It is used for cutting and throttling. The butterfly valve butterfly plate is installed in the diameter direction of the pipeline. In the cylindrical channel of the butterfly valve body, the disc butterfly plate rotates around the axis, and the rotation angle is between 0° and 90°. When it rotates to 900°, the valve is fully opened. The butterfly valve and the butterfly valve stem have no self-locking ability. In order to position the butterfly plate, a worm gear reducer should be installed on the valve stem. The use of the worm gear reducer can not only make the butterfly plate self-locking, but also improve the operating performance of the valve. The streamlined design of the butterfly plate makes the fluid resistance loss small, which can be called an energy-saving product.

Butterfly valve structural features: Butterfly valve structural features:

1. The valve stem is a through-stem structure, which has been quenched and tempered and has good comprehensive mechanical properties, corrosion resistance and scratch resistance. When the butterfly valve is opened and closed, the valve stem only rotates, does not move up and down, the valve stem packing is not easy to be damaged, and the sealing is reliable. It is fixed with the cone pin of the butterfly plate, and the hanging end is designed to prevent the valve stem from falling off when the connection between the valve stem and the butterfly plate is accidentally broken.

2. According to the structure, butterfly valves can be divided into offset plate type, vertical plate type, inclined plate type and lever type. According to the sealing form, they can be divided into relative sealing type and hard sealing type. Soft sealing type is generally sealed with rubber ring, and hard sealing type is generally sealed with metal ring. Metal sealing valves generally have a longer life than elastic sealing valves, but it is difficult to seal completely. Metal sealing can adapt to higher operating temperatures, while elastic sealing has the disadvantage of temperature limitation. Commonly used butterfly valves are clamp butterfly valves, flange butterfly valves and welded butterfly valves. The clamp butterfly valve uses stud bolts to connect the valve between two pipe flanges; the flange butterfly valve has a flange on the valve, and the flanges at both ends of the valve are connected to the pipe flange; the two ends of the welded butterfly valve are welded to the pipeline.

3. The butterfly valve has a simple structure, small size, light weight, low material consumption, small installation size, fast switching, reciprocating rotation of 90°, and small driving torque. Provide good fluid control performance and closing seal. When the butterfly valve is in the fully open position, the thickness of the butterfly plate is the only resistance when the medium flows through the valve body, so the pressure drop generated by the valve is very small, so it has good flow control characteristics.

Butterfly valve flow characteristics:

The operating torque of the butterfly valve has different values ​​due to the opening and closing directions. Horizontal butterfly valves, especially large-diameter valves, cannot be ignored due to the torque generated by the water depth and the difference in the upper and lower lifts of the valve shaft. In addition, when the elbow is installed on the inlet side of the valve, a bias flow will be formed and the torque will increase. When the valve is in the middle opening, the operating mechanism needs to be self-locking due to the effect of the water flow torque.

The relationship between the opening of the butterfly valve and the flow rate is basically an equal percentage change. If it is used to control the flow rate, its flow characteristics are also closely related to the flow resistance of the pipeline. For example, the valve installed on two pipelines has the same diameter and form, but the loss coefficient of the pipeline is different, and the flow rate of the valve will also be very different.

When the butterfly valve is opened in the middle, the opening shape of the valve body and the front end of the butterfly plate is centered on the valve shaft, and different states are formed on both sides. Therefore, the nozzle opening is formed on one side of the valve body and the valve plate, and the throttle opening is formed on the other side. The flow rate on the nozzle side is much faster than that on the throttle side, and negative pressure will be generated under the throttle side valve. The rubber seal is easy to fall off.