The advantages of gate valves are:
①The fluid resistance is small.
②The external force required for opening and closing is small.
③The flow direction of the medium is not restricted.
④When fully open, the sealing surface is less eroded by the working medium than the stop valve.
⑤The body shape is relatively simple, and the casting process is better.
The disadvantages of gate valves are:
①The overall dimensions and opening height are relatively large. The installation requires a lot of space.
② During the opening and closing process, there is relative friction between the sealing surfaces, which can easily cause scratches.
③Gate valves generally have two sealing surfaces, which add some difficulties to processing, grinding, and maintenance.
the type of gate valve
1. Dividable according to the structure of the gate valve
1). Parallel gate valve.
A parallel gate valve is a gate valve whose sealing surface is parallel to the vertical centerline, that is, two sealing surfaces are parallel to each other. The most common type of this kind of gate valve is the double gate type. In order to make the valve body and the two mirrors of the valve plate contact tightly when closed, a double-sided thrust wedge is often used between the two gates. In this way, when the valve is closed, the double-sided thrust wedge contacts with the bottom of the valve body and gradually receives force, and the double gate is removed to make the sealing surface of the gate and the valve body close. This type of double-brake parallel gate is mostly used on low-pressure pipelines such as small pipelines. There are also parallel gate valves that use a single gate, but they are rare.
2). Wedge gate valve.
Wedge gate valve means that the sealing surface is at a fixed angle with the vertical centerline. The higher the temperature of the medium, the greater the inclination angle. To reduce the possibility of wedging the gate when the humidity changes.
In the wedge gate valve, there are single gate discs, double gates, and elastic gates. The single gate wedge gate valve has a simple structure and reliable use, but it has high requirements for the accuracy of the angle of the sealing surface, processing and maintenance are difficult, and the possibility of wedging when the temperature changes are high. Double ram wedge gate valves are often used in water and steam media pipelines. Its advantages are: lower accuracy requirements for the angle of the sealing surface, temperature changes are not easy to cause the phenomenon of wedging, and gaskets can be added to compensate when the sealing surface is worn. However, there are many structural parts of this kind, which are easy to bond in the viscous medium and affect the sealing. More importantly, the upper and lower baffles are prone to rust after long-term use, and the gates are easy to fall off. Elastic gate wedge gate valve, which has the advantages of simple structure and reliable use of single gate wedge gate valve, and can produce a small amount of elastic deformation to compensate for the deviation of the sealing surface angle processing, and improve the processability. It has been widely used.
2. According to the stem structure, gate valves can be divided into:
1). Dark stem gate valve.
The stem nut is in direct contact with the medium in the valve body. When opening and closing the gate, the stem nut is rotated to realize the lifting of the stem. The advantage of this structure is: the height of the closed valve always remains unchanged, so the installation space is small, and it is suitable for places with large diameters or restricted installation space. This structure should be equipped with an opening and closing indicator to indicate the degree of opening and closing. The disadvantage is that the valve stem thread cannot be lubricated, and it is directly corroded by the medium and easily damaged.
2). Rising stem gate valve.
The stem nut is on the valve cover or bracket. When opening and closing the valve, the stem nut is rotated to achieve the lifting of the stem. This kind of structure is beneficial to the lubrication of the valve stem thread, the degree of opening and closing is obvious, and it is widely used.
the diameter of the gate valve shrinks
If the diameter of the passage in a valve body is different (often the diameter at the valve seat is smaller than the diameter at the flange connection), it is called diameter shrinkage.
Diameter 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. The fluid resistance loss increases. In some working conditions (such as oil pipelines in the petroleum sector), valves with reduced diameters are not allowed. On the one hand, it is to reduce the resistance loss of the pipeline, and on the other hand, it is to avoid obstacles to the mechanical cleaning of the pipeline after the diameter shrinks.
Gate valves are widely used in oil pipelines because they have many advantages:
such as small structure length, simpler body shape, and easy casting. When fully opened, the sealing surface is less eroded by the working medium than the stop valve, and the medium flow is not Direction restrictions, etc., the most important thing is the low fluid resistance and easy operation. However, gate valves also have certain shortcomings: the main reason is that they are large in size and require large installation space. They are sealed during opening and closing and relatively friction causes a large amount of wear. Generally, there are two dense injection surfaces, which bring difficulties to processing, grinding, and maintenance. Especially difficult to adjust the flow.