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The Structure and Application of Gate Valves

1. Structural form of gate valve


Industrial valve is a common valve in electric valve products. The main gate valves of gate valve manufacturers have four structures: wedge type elastic single gate valve, wedge type double gate valve, spring preloaded parallel double gate valve and top block parallel double gate valve. In Ni, the diameter DN of the gate valve is generally above 80mm. The body of the nuclear gate valve shall be forged. Casting is permitted only for nuclear grade 2 and 3 gate valve bodies. However, forgings are often used because the quality of castings is not easy to control and guarantee. In order to prevent medium leakage, the gate valve usually adopts double-layer packing with leakage pipe, and is equipped with a disc spring preloading device to prevent the packing from loosening. There are two drive modes: manual and electric. As the electric drive device of the electric gate valve, the influence of the moment of inertia of the motor on the closing force should be considered, and a motor with a braking function should be used to prevent overload.


2. Two ways of connection between the gate valve body and the bonnet


Flange bolted connection and pressure self-sealing bonnet, but flange bolted connection is more common, because this structure is beneficial to increase the lip seal welding, so the seal is more reliable. The four gate valves have different structures and different performances. The wedge-type elastic single gate valve has the characteristics of simple, firm and reliable sealing pair structure, but it has strict requirements on the angle error between the gate valve and the sealing surface of the valve body during manufacture, so it is widely used in the main circuit system. The wedge-type double gate valve structure is a commonly used structure in thermal power plants. Since the angle of the wedge-type double gate valve can be adjusted by itself, the sealing is more reliable and the maintenance is more convenient. Parallel double gate valve spring preload with advantage load door will not rise sharply when closed, but it will spring force at the same time, this door will not disengage from valve seat when opening and closing, the sealing surface is relatively worn, and there are many door seals part, so it is inconvenient to assemble. The parallel double gate valve with the top block makes the two gates staggered along the inclined plane by the top block, so that the gate valve is closed tightly and the sealing is reliable, but there are many sealing parts of the gate valve.


3. In addition to the above four structures, there are also two gate valves without stuffing boxes


One is the hydraulic gate valve, which uses its own pressure water to push the piston to open or close the valve. Since the piston is directly connected to the gate through the valve stem, there is no packing seal and leak points are avoided. However, it is difficult for pistons and cylinders to seal without leakage, so measures should be taken in the control system to keep the pressure stable. The other is a fully enclosed electric gate valve designed and developed by ourselves. The valve uses a special screen to close the motor, and the opening and closing of the gate is completed by a submerged internal planetary reducer. Due to the use of rolling screw pairs, no filler, energy consumption is reduced, operation safety is ensured, and maintenance is simplified. The disadvantage of these two kinds of gate valves is that the structure is complicated and the cost is high.

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