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An overview of gate valve, and its advantages and disadvantages

Gate valve refers to the valve that the closure member (disk) moving along the vertical centerline of the pathway. It's used in pipe only for full-open or full-close, but not for adjustment or choking. Generally, gate valve has been widely used in the cutting devices of DN ≥ 50mm, and sometimes used in the minor-caliber ones, too.

The disk of the most commonly used mode has two sealing surfaces, that form a wedge (the angle of which depends on the valve parameter). Generally, the angle is 50°, when the medium temperature is not high, the angle is only 2°52'. The disk of wedge gate valve can be made to be a whole, called solid wedge. In order to improve the technology, make up the deviation generates in the production process, the disk can also be micro-deformation, which called flexible wedge.

When gate valve closed, the sealing surface can be sealed by the medium pressure, which means the medium pressure push the sealing face to the other side of the seat, it's also named self-sealing. Most of the gate valves are the kind of forced sealing, which means, in order to ensure the leak tightness, the valve relies on the external pressure to push the disk to the seat when it's closing.

The gate valve, when its disk makes straight line movement with the stem, is called rising stem. There always trapezoidal threads one the rising stems. Through the agency of the nuts on the top of the valve and the guide grood on the valve body, the rotary movement is converted into the straight line movement, at the same time, the operating torque turns into operating thrust.

When the valve opens, and the height of the disk upgrades equal to the valve size port, the fluid channel is completely smooth. It's impossible to monitor the height of the disk in the process of the operating, so we usually take the apex of the stem as a symbol. If the apex comes in a fixed position, the valve totally opens. Considering the dead-lock caused by the temperature change, we usually take back 1/2-1 circle after the disk comes to the apex. Therefore, the wide-open valve position is determined by the position of the disk.

The advantages of gate valve

(1) Little fluid resistance. The flowing medium will not change its direction in a through way valve, so the fluid resistance is little.

(2) Open-close torque is little, the operating is labor saving. Compared with the globe valve, the disk of the gate valve is making vertical movement with the flowing direction of the medium, so it's open-close is labor saving.

(3) Medium flowing direction is unrestricted, won't be turbulent flow, and won’t reduce the pressure. Medium can flow in any direction of the both sides of the valve, and can reach the purpose the using. Gate valve is more applicable to the pipe, the direction of the medium in which may be changed.

(4) Face to face dimension is short. The disk of the gate valve is set vertical to the body, the disk of the globe valve is set horizontally, so the face to face dimension of the gate valve is shorter than that of the globe valve.

(5) Efficient sealing. When it is full open, the erosion impact to the sealing surface is little.

(6) When it is full open, the erosion impact to the sealing surface is less than that to the gate valve.

(7) Its shape is relatively simple, the casting technology is good, and the scope of application is wide.

The disadvantages of gate valve

(1) The sealing surface is easily to be damaged. There is relative friction between the disk and the two sealings which get to the seat, so the sealing surface is easily to be damaged. The service life span will be also influenced, and the maintenance is not easy.

(2)The gate valve must be full-open or full-close, the journey the disk takes is long, so the space when the valve opening occupies is large. The external dimensions is big,
the gate valve requires larger space for installation.

(3) The structure is complex. Generally, there are two sealings on the gate valve, so the number of the difficult parts is larger, the task of producing and maintence is arduous, and its cast is also higher than the globe valve.

The contraction of the bore

If the diameter of the valve passage is not the same, it's called the contraction of the bore. The contraction may shrink the size of the part, the power when the valve open/close needs will reduce, and the scope of the parts' application is also expanded, but the fluid resistance loss will increased.

Under some certain working conditions of some certain departments (such as the pipeline of the oil sector), it is not allowable to use this kind of valve. On the one hand, it is in order to reduce the loss of pipeline resistance, on the other hand, to avoid the mechanical cleaning obstacle caused by the contraction of the bore.

 

 

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