Turbine main valve-4

Release time:

2024-08-03

Type of main valve

2) butterfly plate. The butterfly plate is installed in the valve body through the upper and lower shafts. When the butterfly valve is in the fully closed position, the butterfly plate bears all the water pressure. When it is in the fully open position, it is in the water flow center. Therefore, the butterfly plate should not only have enough strength and rigidity, but also have good hydraulic performance to reduce the hydraulic loss. The butterfly plate is made of cast iron or cast steel into diamond, lens and flat shape. Among them, diamond shaped butterfly plate is suitable for low head unit; lens shaped butterfly plate is suitable for high head unit; flat shaped butterfly plate is connected by two plates and a number of downstream reinforcement plates, and the two plates also flow through each other, with small hydraulic loss. When fully closed, the rigidity of bearing water pressure is large and the sealing performance is good, so it is suitable for high head unit.

Driven by the operating mechanism, the butterfly plate rotates around the shaft in the valve body. In order to form the moment of closing the butterfly plate when closing the main valve, the center line of the upper and lower shafts and the butterfly plate is generally double eccentric or triple eccentric. The area difference between the upper and lower axes is about 8% ~ 10%. The rotation angle of most butterfly plates to the water flow center line is 75 ° ~ 80 °, so as to compress the valve body seal when the butterfly plates are fully closed. The flow passage surface of butterfly plate is arch structure to increase the flow passage capacity.

3) sealing device. When the butterfly valve is closed, there will be water leakage between the end of the butterfly plate at the connection between the valve body and the upper and lower valve shafts, and between the outer circle of the butterfly plate and the sealing surface of the valve body. Therefore, the two places are equipped with sealing devices, and the sealing forms are divided into end sealing and circumference sealing.

A. end seal. There are many forms of end seal, such as bronze expansion ring end seal, pressure self compensation combination seal, etc. The best effect is bronze expansion ring end seal, which is suitable for butterfly valve with smaller diameter. The pressure self compensation combined seal is suitable for the butterfly valve with large diameter.

B. circumferential seal. Circumference seal is also called main seal. There are two kinds of common circumference seal: compression type and air shroud type.

The seal seat of the compression type circumferential seal valve body is welded on the valve body by overlaying stainless steel or integral stainless steel ring. In order to prolong the service life of the seal seat, its surface roughness Ra is not more than 0.8um. The whole ring of solid high hard oil-resistant rubber with hardness of 75shorea is used for sealing the butterfly plate, and the rubber ring is pressed on the butterfly plate with stainless steel pressing plate. When the butterfly plate is placed in the fully open position, the sealing ring can be repaired or replaced without disassembling the valve body. When the butterfly plate is in the fully closed position, the sealing ring of butterfly plate has the maximum pressing capacity under the influence of water pressure. When the downstream pipeline of butterfly valve is filled with water, the back pressure is formed, and the pressing capacity is gradually reduced. The sealing and pressing amount can be fine adjusted by stainless steel pressing plate, and the pressing amount is 0.5 ~ 2mm.

After accurate calculation of rigidity and adjustment of sealing ring compression, the leakage of butterfly valve during sealing test and commercial operation can be within the allowable range of the standard.