Type of gate valve
According to the structure of the gate can be divided into 1) parallel gate valve: the sealing surface and the vertical center line parallel, that is, the two sealing surfaces parallel to the gate valve.
In the parallel gate valve, the structure with thrust wedge is most often seen. There is a double-sided thrust wedge in the middle of the two gates. This gate valve is suitable for low pressure medium and small diameter (DN40-300mm) gate valves. There is also a spring between the two gates, the spring can generate a pre-tightening force, which is conducive to the sealing of the gate.
2) Wedge gate valve: The sealing surface and the vertical center line are at a certain angle, that is, the two sealing surfaces are wedge-shaped gate valves.
The inclination angle of the sealing surface is generally 2° 52 Ì, 3° 30 Ì, 5°, 8°, 10°, etc. The angle depends on the temperature of the medium. The higher the general operating temperature, the greater the angle that should be taken to reduce the possibility of wedges during temperature changes.
In the wedge gate valve, there is a single gate, double gate and flexible gate. The single gate wedge gate valve has a simple structure and is reliable in use. However, it requires a high precision for the angle of the sealing surface, and it is difficult to process and maintain. The possibility of wedges is large when the temperature changes. Double gate wedge gate valves are used more often in water and vapour medium lines.
Its advantages are: lower requirements on the accuracy of the sealing surface angle, the phenomenon of the wedge does not easily occur due to temperature changes, and gasket compensation can be added when the sealing surface is worn. However, many of these structural parts are easily bonded in viscous media and affect sealing.
The main reason is that the upper and lower baffles are prone to rust for a long time and the gates are easy to fall off. Flexible gate wedge gate valve, it has a single gate wedge gate valve structure is simple, use the advantages of *, but also produce a slight amount of elastic deformation to compensate for the deviation of the sealing surface angle process, improve the process, has been a lot use.
2, according to the structure of the valve stem valve can be divided into 1) open rod valve: stem nut on the valve cover or bracket, open and close the gate, with a rotary valve stem nut to achieve the lifting of the stem. This kind of structure is beneficial to the lubrication of the valve stem, and its opening and closing is obvious, so it is widely used.
2) Dark rod valve: The stem nut is in the valve body and is in direct contact with the media. When opening and closing the gate, use a rotary valve stem. The advantage of this structure is that the height of the gate valve always remains the same, so the installation space is small and it is suitable for large diameter or gate valves with limited installation space. This structure should be equipped with open and close indicators to indicate the degree of opening and closing. The disadvantage of this structure is that the stem thread not only cannot be lubricated, but also directly accepts media erosion and is easily damaged.
Gate valve diameter shrinkage
If the diameter of a channel in a valve body is not the same (usually the diameter at the valve seat is smaller than the diameter at the flange connection), it is called the diameter contraction.
Diameter shrinking can reduce the size of parts, reduce the required force for opening and closing, and at the same time expand the application range of parts. But after the diameter shrinks. The fluid resistance loss increases.
Under certain working conditions in certain sectors (such as oil pipelines in the petroleum sector), the use of bore-reduced valves is not allowed. This aspect is to reduce the resistance loss of the pipeline and, on the other hand, to avoid obstacles to the mechanical cleaning of the pipeline after its diameter shrinks.
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