1. The definition of the gate valve It is a kind of valve widely used in the pipeline, which mainly plays the role of connecting and truncating the medium. It is not suitable for regulating the flow of the medium, but it can judge the flow size according to the height of the stem lifting (such as the elastic seat seal gate valve with opening and closing scale for fire fighting). Compared with other valves, The requirements for the range of application of the
gate valve are wide such as the pressure, temperature, caliber and so on.
2. The structure of the gate valve Gate valves can be divided into the wedge type single gate, elastic gate, double gate and parallel gate according to the different internal structures.
The support of different stems can be divided into rising stem gate valves and non-rising stem gate valves.
3. The valve body and flow channel The structure of the gate valve body determines the connection between the valve body and the pipeline, and the valve body and the valve cover. In terms of manufacturing methods, there are casting, forging, forging welding, casting welding and tube plate welding. The forged valve body has developed to the direction of large calibers. The casting valve body has gradually developed to small calibers. Any kind of gate valve body can be forged. It also can be cast, according to the requirements of the means of the manufacturing of the user and the manufacturer.
The channel of the gate valve body can be divided into full bore type and reduced bore type. The flow aperture smaller than the nominal flow through the valve is called a reduced bore. There are two kinds of reducing shapes: uniform reducing shapes and uniform reducing shapes. The cone-shaped flow channel is a nonuniform reduction. The aperture of the inlet end of this kind of valve is basically the same as the nominal diameter. Then, the inlet gradually shrinks to the minimum at the seat.
The reduced bore flow channel is used (whether taper shaped non-uniform reduction or uniform reduction). Its advantage is the same size of the valve. It can reduce the size of the gate, opening and closing force and torque.
The disadvantage is listed as follows. The flow resistance increases and the pressure drop and the energy consumption increase, so the shrinkage hole should not be too large. For taper, compared to the nominal diameter, the ratio of valve seat diameter is usually 0.8 to 0.95. If the nominal diameter is less than 250mm, the inner diameter of the valve seat is generally one step lower than the nominal diameter.
4. Motion mode of the gate valve When the gate valve is closed, the sealing surface can only rely on the medium pressure to seal, that is, it only relies on the medium pressure to press the sealing surface of the gate to the seat on the other side to ensure the sealing of the sealing surface. Most gate valves are forced to seal. That is, when the valve is closed, the external force must be forced to press the gate to the seat to ensure the sealing surface.
Mode of motion: The gate valve's gate plate moves in a straight line with the valve stem. It is also called the rising stem gate valve. Usually, there is a ladder thread on the lifting rod through the nut at the top of the valve and the guide groove on the valve body. The rotating motion changes into a straight motion. That is, the operating torque changes into the operating thrust accordingly. When the valve is opened, the path of the fluid is completely clear when the ram elevation is equal to 1:1 of the valve diameter, but this position cannot be monitored during operation. In actual use, the apex of the stem is used as a symbol. The fully open position of the valve is determined by the position of the ram (stroke). Some stem nut of gate valves is located on the gate plate, and the hand wheel rotates to drive the valve stem to rotate, and the gate plate is lifted. This kind of valve is called a rotating rod gate valve or non-rising stem gate valve.
