Working principle and flow characteristics of butterfly valve

 Butterfly valve is a kind of valve which uses round butterfly plate as the opening and closing part and rotates around the valve axis to open, close and regulate the fluid channel. It is mainly used for cutting off and throttling in the pipeline. The butterfly plate of butterfly valve is installed in the diameter direction of pipeline. In the cylindrical passage of the butterfly valve body, the disc-shaped butterfly plate rotates around the axis with a rotation angle of 0 ° C~90 ° C; Between, rotate to 90 ° C, the valve is fully open. Butterfly valve and butterfly rod have no self-locking ability. In order to locate the butterfly plate, worm gear reducer should be installed on the valve rod. Using worm gear reducer can not only make the butterfly plate have self-locking ability, make the butterfly plate stop at any position, but also improve the operation performance of the valve. The streamline design of the butterfly plate can reduce the loss of fluid resistance, so it is an energy-saving product.

Flow characteristics of butterfly valve:

The relationship between the opening of butterfly valve and flow is basically equal percentage change. If it is used to control the flow, its flow characteristics are also closely related to the flow resistance of the piping. For example, the diameter and form of the valves installed in the two pipelines are all the same, and the flow rate of the valves will vary greatly with the loss coefficient of the pipelines.

When the butterfly valve is in the middle opening, the opening shape formed by the valve body and the front end of the butterfly plate is centered on the valve shaft, and the two sides form different states. The front end of the butterfly plate on one side moves along the flow direction, and the other side moves against the flow direction. Therefore, the valve body and the valve plate on one side form a nozzle like opening, and the other side is similar to an orifice like opening, Negative pressure will be generated under the throttle side valve, and the rubber seal will often fall off.

The operating torque of butterfly valve is different due to different opening degree and opening and closing direction of the valve. The torque of horizontal butterfly valve, especially large diameter valve, due to the water depth and the difference between the upper and lower ends of the valve shaft can not be ignored. In addition, when the elbow is installed at the inlet side of the valve, the deflection flow will be formed and the torque will be increased. When the valve is in the middle opening, the operating mechanism needs to be self-locking due to the action of hydrodynamic moment.

Structural features of butterfly valve:

1. The butterfly valve has the advantages of simple structure, small volume, light weight, low material consumption, small installation size, quick switch and high efficiency ° C; It is used to cut off, connect and adjust the medium in the pipeline. It has good fluid control characteristics and sealing performance. 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 through the valve is very small, so it has good flow control characteristics.

2. The valve stem is a through rod structure. After quenching and tempering, it has good comprehensive mechanical properties, corrosion resistance and scratch resistance. When the butterfly valve is opened and closed, the valve stem only rotates without lifting. The packing of the valve stem is not easy to be damaged and the seal is reliable. It is fixed with the taper pin of the butterfly plate, and the extended end is designed to prevent the valve stem from collapsing when the connection between the valve stem and the butterfly plate breaks accidentally.

3. Butterfly valve according to the structure can be divided into offset plate, vertical plate, inclined plate and lever type. According to the sealing form, it can be divided into two types: relatively sealed type and hard sealed type. The soft seal type is usually sealed with rubber ring, while the hard seal type is usually sealed with metal ring. The service life of the valve with metal seal is generally longer than that with elastic seal, but it is difficult to achieve complete seal. Metal seal can adapt to higher working temperature, while elastic seal is limited by temperature. There are three kinds of butterfly valves in common use: clip type butterfly valve, flange type butterfly valve and butt welding type butterfly valve. Clip on butterfly valve is connected between two pipe flanges by stud bolts; Flange butterfly valve is a kind of valve with flange, which is connected to the pipe flange by bolts; The two end faces of butt welding butterfly valve are welded with the pipeline.