Butterfly Valve Use

- May 13, 2020-

Butterfly valve use


The butterfly plate of the butterfly valve is installed in the diameter direction of the pipe. The butterfly valve is simple in structure, small in size and light in weight. It consists of only a few parts, and it can be opened and closed quickly by rotating 90 °. The operation is simple, and the valve has good fluid control characteristics. When the butterfly valve is in the fully open position, the thickness of the butterfly plate is the resistance when the medium flows through the valve body, so the pressure drop generated by the valve is small, so it has good flow control characteristics.

If butterfly valves are required for flow control, the main thing is to choose the correct valve size and type. The structural principle of the butterfly valve is particularly suitable for making large-caliber valves. Commonly used butterfly valves are wafer type butterfly valves and flange type butterfly valves. Wafer type butterfly valve is used to connect the valve between two pipeline flanges with stud bolts. Flange type butterfly valve is equipped with flanges on the valve, and the two ends of the valve are bolted to the pipeline flange using bolts.

Butterfly valve as a component used to realize the on-off and flow control of the pipeline system has been widely used in many fields such as petroleum, chemical industry, metallurgy, hydropower and so on. In the known butterfly valve technology, a sealing structure is mostly adopted in the sealing form, and the sealing material is rubber, polytetrafluoroethylene, or the like. Due to the limitation of structural characteristics, it is not suitable for industries such as high temperature resistance, high pressure, corrosion resistance and wear resistance.

A relatively advanced butterfly valve is a three-eccentric metal hard-seal butterfly valve. The valve body and the valve seat are conjoined members. The sealing surface layer of the valve seat is welded with a temperature-resistant and corrosion-resistant alloy material. The multi-layer soft stack type sealing ring is fixed on the valve plate. Compared with the traditional butterfly valve, this type of butterfly valve has high temperature resistance, light operation, and no friction during opening and closing. When closing, the torque of the transmission mechanism increases to compensate the seal, which improves the butterfly valve. The advantages of sealing performance and extended service life.

However, the following problems still exist in the use of this butterfly valve:

First, because the multi-layer soft and hard stacked seals are fixed on the valve plate, when the valve plate is normally open, the medium will scour the sealing surface. After the soft sealing tape in the metal sheet sandwich is washed, it will directly affect the sealing performance.

2. Due to the structural conditions, the structure is not suitable for valves with a diameter below DN200, because the overall structure of the valve plate is too thick and the flow resistance is large.

3. Due to the principle of triple eccentric structure, the seal between the sealing surface of the valve plate and the valve seat is based on the torque of the transmission device to press the valve plate towards the valve seat. In the positive flow state, the higher the pressure of the medium, the tighter the seal squeezes. When the medium in the flow channel reverses, as the medium pressure increases, the unit positive pressure between the valve plate and the valve seat is less than the medium pressure, and the seal begins to leak.

The high-performance three-eccentric bidirectional hard-seal butterfly valve is characterized in that the valve seat seal ring is composed of multiple layers of stainless steel sheets on both sides of a soft T-shaped seal ring. The sealing surface of the valve plate and the valve seat is an oblique cone structure, and a temperature-resistant and corrosion-resistant alloy material is overlaid on the oblique cone surface of the valve plate; a structure in which a spring fixed between the adjusting ring pressure plate and an adjustment bolt of the pressure plate are assembled together.

This structure effectively compensates the tolerance band between the shaft sleeve and the valve body and the elastic deformation of the valve stem under the pressure of the medium, and solves the sealing problem of the valve during the two-way interchangeable medium conveying process. Adopting soft T-shaped multilayer stainless steel sheets on both sides to form the seal ring, which has the dual advantages of metal hard seal and soft seal. It has zero leakage sealing performance under low and high temperature conditions.

The test proves that in the positive flow state of the pool (the direction of medium flow is the same as the direction of rotation of the butterfly plate), the pressure on the sealing surface is caused by the torque of the transmission device and the effect of the medium pressure on the valve plate. The tighter the oblique conical surface of the valve plate and the sealing surface of the valve seat when the forward medium pressure increases, the better the sealing effect. In the reverse flow state, the seal between the valve plate and the valve seat is pressed against the valve seat by the torque of the driving device. With the increase of the reverse medium pressure, when the unit positive pressure between the valve plate and the valve seat is smaller than the medium pressure, the deformation stored by the spring of the adjusting ring after loading can compensate the tight pressure on the sealing surface of the valve plate and the valve seat. Play the role of automatic compensation. Therefore, unlike the prior art, the utility model does not install a soft and hard multilayer sealing ring on the valve plate, but directly installs it on the valve body. Adding an adjusting ring between the pressure plate and the valve seat is a very ideal two-way hard sealing method. . It will replace gate, globe and ball valves.