Gate valve basic knowledge

Gate valve is the closing member (gate) along the centerline of the vertical movement of the valve. Gate valve is mainly used in the pipeline cut off. Gate valve is a widely used type of valve, the general caliber DN ≥ 50mm cutting devices are used it, and sometimes a small caliber shut-off device is also used gate valve. First, the advantages of gate valve 1, fluid resistance is small. 2, external force required for opening and closing smaller. 3, the flow of medium is not limited. 4, fully open, the sealing surface by the erosion of the working medium smaller than the stop valve. 5, the shape is relatively simple, casting technology is better. Second, the shortcomings of the valve 1, the overall dimensions and the opening height are larger. Installation requires more space. 2, the process of opening and closing, there are relative friction between the sealing surface, easily lead to abrasions. 3, the gate valve generally has two sealing surfaces, to the processing, grinding and maintenance to increase some difficulties. Third, the type of gate valve 1, according to the structure of the gate can be divided 1) parallel gate valve: sealing surface and the vertical center line parallel to the two sealing surfaces parallel to each other gate valve. In parallel gate valves, the structure with thrust wedges is the most common, with double-sided thrust wedges in the middle of the two gate plates. This type of gate valve is suitable for low pressure medium and small bore (DN40-300mm) gate valves. There is also a spring between the two rams, the spring can produce preload, is conducive to the gate seal. 2) wedge gate valve: sealing surface and the vertical center line into a certain angle, that is, two sealing surface into a wedge-shaped gate valve. The sealing surface of the tilt angle is generally 2 ° 52 °, 3 ° 30 °, 5 °, 8 °, 10 °, the size of the angle depends on the medium temperature level. The higher the general operating temperature, the angle taken should be greater in order to reduce the possibility of wedging occurs when the temperature changes. In the wedge gate valve, there is a single gate, double gate and elastic gate of the points. Single gate wedge gate valve, simple structure, reliable, but the sealing surface angle of the higher precision, processing and maintenance more difficult, wedges the possibility of temperature changes great. Double gate wedge gate valve in the water and steam medium pipe used more. Its advantages are: low precision of the sealing surface angle, the temperature change is not easy to cause wedging phenomenon, the sealing surface wear, you can add gasket compensation. However, this structure more parts in the viscous medium easy to bond, affecting the seal. More importantly, the long-term use of the lower bezel easy to produce corrosion, easy to fall off the gate. Flexible gate wedge gate valve, it has a single gate wedge gate valve structure is simple, the use of * can have the advantage of producing a small amount of elastic deformation make up the sealing surface angle of the process of deviation, improve the process, has been a large number use. 2, according to the structure of the valve stem can be divided into 1) Ming rod valve: stem nut in the valve cover or bracket, open the gate, the use of rotating stem nut to achieve stem lifting. This structure is beneficial to the lubrication of the valve stem, opening and closing a clear degree, it is widely used. 2) dark bar gate valve: stem nut in the valve body, and the media in direct contact. Open and close the gate, the rotary valve stem to achieve. The advantage of this structure is that the height of the gate valve always remains unchanged, so the installation space is small, suitable for large-caliber or gate valves with limited installation space. This structure should be equipped with an opening and closing indicator to indicate the degree of opening and closing. The disadvantage of this structure is that not only is the stem thread unlubricated, but it is also subject to direct media erosion and damage. Fourth, the valve diameter of the valve contraction If the channel diameter of a valve body is not the same (often at the valve seat diameter less than the diameter of the flange connection), known as the diameter of the contraction. Path contraction can reduce the size of the parts, opening and closing the corresponding reduction in force required, while expanding the scope of application of components. However, after the path of contraction. Fluid resistance loss increases. Under certain operating conditions in certain sectors (such as oil pipelines in the petroleum sector), valves with reduced diameter are not allowed. This is done on the one hand to reduce the loss of resistance on the part of the pipeline and on the other hand to avoid obstacles to the mechanical cleaning pipeline after the shrinkage of the path.

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