The valve body of the ball valve is produced by welding six partially forged shells after assembly. The structure is compact and the whole ball valve is integrated. At present, the large-caliber ball valves used in production are mostly split three-piece structures, and each part is connected by bolts. Compared with the three-piece ball valve, under the same strength, the wall thickness of the fully welded ball valve forge piece can be made to be very thin, the valve weight can be reduced by a quarter, and the resistance to pipeline bending and extrusion is enhanced.
According to the form of the ball, the ball valve can be divided into two types: fixed ball and floating ball. The product generally adopts a floating ball structure. Under the pressure of the medium, the ball is pressed tightly on the sealing surface of the outlet end to achieve the purpose of sealing. Once the pressure difference between the inlet and outlet of the valve body is large, it is often difficult to open due to the large torque. The fully welded ball valve uses a high-strength satin steel valve stem, supported by a stainless steel bearing covered with PTFE, which rotates smoothly and accurately.
When the ball valve is nearly being fully closed or just opened, the narrow point between the ball valve and the valve seat is scoured at high speed due to the fluid being throttled into high-speed turbulent flow, which becomes the most severely worn area of the seal of the valve seat. The valve seat upstream and downstream of the fully welded ball valve is rotated 15 degrees by the paddles on the valve ball, so that the entire sealing surface of valve seat is washed by fluid in turn, and the same part is washed again after the valve is opened or closed 12 times. The wear of entire valve seat remains the same and the working life is greatly extended.
The sealing material PFFE in the upper area of the valve stem of the fully welded ball valve is a low-friction and aging-resistant material with a long service life. The valve stem of fully welded ball valve is also equipped with a sealing grease injection system. Even if foreign matter enters the ball valve seat and damages the sealing surface, it can still be injected with special sealing grease through the secondary valve seat to maintain the seal. Conventional ball valves do not have a sealing grease injection structure. Once the sealing surface is damaged and internal leakage occurs, we can only replace the entire ball valve.
Although the ball valve adopts the upstream and downstream double valve seat to achieve isolation and seal, the valve seat will be inevitably worn in long-term operation; when the valve is closed, the upstream valve seat may have a certain internal leakage, and the internal leakage medium enters the valve ball cavity. The fully welded ball valve is equipped with a pressure release pipeline connected to the middle cavity and leads the pressure release pipeline out of the ground. Regardless of whether the valve is in the fully open or fully closed position, the valve cavity shut-off valve can be opened to release the pressure in the middle cavity. By releasing the cavity pressure can also test the sealing performance of the valve seat.
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