Basic knowledge of the hottest gate valve

2022-09-22
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Basic knowledge of gate valve

gate valve refers to the valve whose closing part (gate) moves vertically along the center line of the passage. The gate valve is mainly used for cutting off in the pipeline

gate valve is a widely used valve. It is generally used for cutting-off devices with a diameter of DN 50mm, and sometimes the result display valve is also used for cutting-off devices with a small diameter

I. advantages of gate valve

1. Low fluid resistance

2. The external force required for opening and closing is small

3. The flow direction of medium is unlimited

4. When fully opened, the erosion of the sealing surface by the working medium is smaller than that of the stop valve

5. The shape is relatively simple and the casting process is good

II. Disadvantages of gate valve

1. The overall dimension and opening height are large. Large space is required for installation

2. During the opening and closing process, there is relative friction between the sealing surfaces, which is easy to cause scratch

3. Gate valves generally have two sealing surfaces, which increases some difficulties in processing, grinding and maintenance

III. type of gate valve

1. According to the structure of the gate, it can be divided into

1) parallel gate valve: the sealing surface is parallel to the vertical centerline, that is, the gate valve with two sealing surfaces parallel to each other

among the parallel gate valves, the structure with thrust wedge is the most common. There are double-sided thrust wedges between the two gate valves. This kind of gate valve is suitable for low-pressure medium and small diameter (Dn40 300mm) gate valves. There are also springs between the two rams, which can produce pre tightening force, which is conducive to the sealing of the ram that can be operated by one hand

2) wedge gate valve: the sealing surface forms an angle with the vertical center line, that is, the two sealing surfaces form a wedge-shaped gate valve

the inclination angle of the sealing surface is generally 252?, 3 30?, 5, 8, 10, etc. the size of the angle mainly depends on the medium temperature. Generally, the higher the working temperature is, the larger the angle should be, so as to reduce the possibility of wedging when the temperature changes

among wedge gate valves, there are single gate, double gate and elastic gate. The single gate wedge gate valve is simple in structure and reliable in use, but it has high requirements for the accuracy of the angle of the sealing surface, and it is difficult to process and maintain. It is very possible to wedge when the temperature changes. Double gate wedge gate valves are widely used in water and steam medium pipelines. Its advantages are: the accuracy of the angle of the sealing surface is low, and the temperature change is not easy to cause wedging. When the sealing surface is worn, gaskets can be added to compensate. However, there are many structural parts of this kind, which are easy to bond in viscous medium and affect the sealing. More importantly, the upper and lower baffles are easy to rust and the ram is easy to fall off after long-term use. The elastic wedge gate valve has the advantages of single wedge gate valve structure, easy to use after the spraying team knows the customer's needs, and can produce a small amount of elastic deformation to make up for the deviation caused by the working piston moving downward by its own weight during the angle processing of the sealing surface, and improve the manufacturability. It has been widely used

2. According to the structure of the valve stem, the gate valve can be divided into

1) rising stem gate valve: the valve stem nut is on the bonnet or support. When opening and closing the gate, rotate the valve stem nut to realize the rise and fall of the valve stem. This structure is beneficial to the lubrication of the valve rod, and the opening and closing degree is obvious, so it is widely used

2) Non rising stem gate valve: the valve stem nut is in the valve body and is in direct contact with the medium. When opening and closing the ram, rotate the valve rod. The advantage of this structure is that the height of the gate valve always remains the same, so the installation space is small. It is suitable for gate valves with large diameter or limited installation space. This structure should be equipped with an opening and closing indicator to indicate the opening and closing degree. The disadvantage of this structure is that the valve rod thread is not only unable to lubricate, but also directly eroded by the medium, which is easy to be damaged

IV. diameter contraction of gate valve

if the channel diameter in a valve body is different (usually the diameter at the valve seat is smaller than that at the flange connection), it is called diameter contraction

path shrinkage can reduce the size of parts, reduce the force required for opening and closing, and expand the application range of parts. But after the diameter shrinks. Fluid resistance loss increases

under certain working conditions in some departments (such as oil pipelines in oil departments), it is not allowed to use valves with reduced diameters. On the one hand, this is to reduce the resistance loss of the pipeline, and on the other hand, it is to avoid the obstacles caused by the shrinkage of the drift diameter to the mechanical cleaning of the pipeline

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