What is the structural difference between a parallel gate valve and a wedge gate valve?

Globe valves and gate valves in the structure.

This article begins with a look at what.

It is a parallel gate valve.

That is, the sealing surface is parallel to the vertical centerline, so the sealing surface on the valve body and the ram is also parallel to each other. The most common type of gate valve is double gate type, in order to make the valve body and the gate two sealing surfaces contact tightly, often use the double-sided thrust wedge clamped between the two rams. In this way, when the valve is closed, the double-sided thrust secondary block is in contact with the bottom of the valve body and is gradually stressed, and the double ram is pushed open so that the sealing surface of the ram is sealed and close to the valve body.

This kind of double ram parallel gate is mostly used on low-pressure pipelines such as small pipelines. Parallel gate valves also use a single gate, but it is rare.

That is, the sealing surface is at a certain angle to the vertical centerline, and the higher the temperature of the medium, the greater the tilt angle, so as to reduce the possibility of wedge when the temperature changes.

The gate of the wedge gate valve is both single and double. The advantages of the double ram type are that the accuracy of the sealing and angle is low, the temperature change is not easy to wedge the ram, and the gasket can be compensated for the wear of the sealing surface.

The disadvantage is that the structure is complex, easy to stick in dry media, and more importantly, the upper and lower baffles are easy to fall off after being corroded for many years. Although the single ram has the shortcomings such as high accuracy requirements of sealing and angle, difficult processing and temperature change may make the ram wedged, the structure is simple, the use is reliable, especially after changing to the elastic ram, it can produce the slight most elastic deformation to make up for the deviation generated in the processing of the angle of the sealing surface, so it is widely used at present.

Here are some of the well-known brands recognized in the valve industry, which are widely recognized and have a high reputation. While rankings may vary depending on time and market conditions, the following brands are generally considered to be among the top brands in the valve industry:

The following are the top ten domestic first-line valve brand manufacturers in 2022-2023, but for reference only: Suzhou Neway Valve Co., Ltd., Shanghai Guanlong Valve Machinery, Shanghai Qizhong Valve Manufacturing, Sanhua, Su Yan, Shentong, Su Valve, Nanfang, Jiang.

First, the word Yao. The above manufacturers are only estimates and references, and the specific situation may vary or fluctuate at any time due to changes in a series of factors such as changes in the market, the size of the competition pattern, and the stability of product quality. As an indispensable key device in industrial production and civil facilities, the quality and reputation of the valve brand directly affect the satisfaction and trust of users.

These brands are known in the valve industry for their innovative technology, high-quality products and reliability. It is important to note that the market and industry are evolving rapidly, and different rankings may vary depending on time and region. For the most up-to-date ranking information, it is recommended to refer to industry reports, professional organizations or market research data for more detailed and accurate information.

Types of gate valves.

1.It can be divided according to the structure of the ram.

In the parallel gate valve, the structure with thrust wedge is the most common, which has a double-sided thrust wedge in the middle of the two gate plates, and this kind of gate valve is suitable for low-pressure small and medium-diameter (DN40-300mm) gate valves. There are also springs between the two rams, and the springs can generate tight force, which is conducive to the sealing of the rams.

2) Wedge gate valve: the sealing surface is at a certain angle to the vertical centerline, that is, the two sealing surfaces are wedge-shaped. The inclination angle of the sealing surface is generally 2052,3930,5.

8。，10。The size of the angle mainly depends on the temperature of the medium.

Generally, the higher the operating temperature, the larger the angle should be taken to reduce the possibility of wedge in the event of temperature changes. In the mode gate valve, there are single rams, double rams and elastic rams. The single gate mode gate valve has a simple structure and reliable use, but it has high requirements for the accuracy of the sealing surface angle, which is difficult to process and maintain, and the possibility of wedge is great when the temperature changes.

Double gate mode gate valves are mostly used in water and vapor medium pipelines. Its advantages are: the accuracy of the sealing surface angle is low, the temperature change is not easy to cause the phenomenon of wedge, and the gasket can be added to compensate when the sealing surface is worn.

However, there are many parts of this structure, which are easy to bond in viscous media and affect the sealing. The main thing is that the upper and lower baffles are easy to rust when used for a long time, and the ram is easy to fall off. The elastic gate wedge gate valve, which has the advantages of simple structure and reliable use of single gate wedge gate valve, can produce a small amount of elastic deformation to make up for the deviation generated in the processing process of the sealing surface angle, and improve the manufacturability, has been widely adopted.

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

1) Open rod gate valve: the stem nut is on the valve cover or bracket, and when the gate is opened and closed, the stem nut is rotated to realize the lifting of the valve stem. This structure is beneficial to the lubrication of the valve stem and has a clear degree of opening and closing, so it is widely used.

2) Dark rod gate valve: the stem nut is in the valve body, which is in direct contact with the medium. When opening and closing the gate, it is achieved by rotating the valve stem.

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 the stem thread not only cannot be lubricated, but also directly accepts the erosion of the medium and is easily damaged.

2. If the diameter of the channel in a valve body is not the same (often the diameter at the valve seat is smaller than the diameter at the flange connection), it is called the diameter shrinkage. The diameter shrinkage can reduce the size of the part, reduce the force required to open and close the part accordingly, and at the same time expand the application range of the part. But after the diameter shrinks.

The loss of fluid resistance increases. Under certain operating conditions in certain sectors (e.g. pipelines in the oil sector), valves with reduced bore are not permitted. On the one hand, this is to reduce the resistance loss of the pipeline, and on the other hand, it is to avoid the obstacle caused by the shrinkage of the bore to the mechanical cleaning pipeline.

The difference between a gate valve and a globe valve is as follows:

Sealing surface. The sealing surface of the gate valve globe valve is a small trapezoidal side of the valve core (depending on the shape of the valve core), once the valve core falls off, it is equivalent to the valve closing (if the pressure difference is large, of course, the closure is not strict, but the anti-reverse effect is not bad), the gate valve is sealed by the side of the valve core gate, the sealing effect is not as good as the globe valve, and the valve core is not as good as the valve is closed.

Flow. The gate valve is a two-way valve, which has no requirements for the inlet and outlet ends of the flow in the pipeline, while the shut-off valve has a flow direction requirement, and only allows the fluid medium to flow in one direction.

Flow resistance. The gate valve is only allowed to be fully open and fully closed, and when the whole pipeline flow channel is in the fully open state, there is no obstruction, and the pressure loss of the medium is minimal. The globe valve is used for flow regulation, and the resistance to the flow of the medium is greater.

Maintenance process. When the gate valve is maintained and overhauled, the valve needs to be removed from the pipeline, and the valve seat and disc of most of the globe valves can be replaced without removing the entire valve from the pipeline. Therefore, the globe valve is more suitable for the occasion where the valve and the pipeline are welded into one.

The difference between the selection of Zhidong and the globe valve mainly depends on the difference between the gate valve and the globe valve.

1.The structure is different. The gate valve is more complex than the globe valve, the height size is larger, the gate valve is shorter and higher than the stop valve of Viton VTON from the appearance, especially the open rod gate valve needs a higher height space, which should be paid attention to in the case of limited installation space.

2.The sealing surface is different. When the Vton gate valve is opened and closed, the valve core and the sealing surface of the valve seat are always in contact and rub against each other, so the sealing surface is easy to wear, especially when the valve is close to the closed state, the pressure difference between the front and rear of the valve core is very large, and the sealing surface is more seriously worn;

The sealing surface of the gate valve has a certain self-sealing ability, and its valve core is tightly in contact with the sealing surface of the valve seat by the medium pressure to achieve tightness and no leakage. The spool inclination of the wedge gate valve is generally 3 6 degrees, and the spool is easy to get stuck when the forced closing is excessive or the temperature changes greatly. Therefore, the high-temperature and high-pressure wedge-shaped gate valve has taken certain measures to prevent the valve core from jamming in the structure.

When the gate valve is opened and closed, the valve core and the sealing surface of the valve seat are always in contact and rub against each other, so the sealing surface is easy to wear, especially when the valve is close to the closed state, the pressure difference between the front and rear of the valve core is very large, and the wear of the sealing surface is more serious.

Compared with the globe valve, the main advantage of the gate valve is that the fluid flow resistance is small, the flow resistance coefficient of the ordinary gate valve is about, and the resistance coefficient of the ordinary globe valve is about. The opening and closing force is small, and the medium can flow in both directions. The disadvantage is that the structure is complex, the height size is large, and the sealing surface is easy to wear.

The sealing surface of the globe valve must be closed by forced force to achieve the seal, and the driving torque of the globe valve is several times that of the gate valve under the same caliber, working pressure and the same driving device. This point should be paid attention to when adjusting the torque control mechanism of the electric valve.

The sealing surfaces of the globe valve are in contact with each other only when they are completely closed, and the relative slippage between the spool and the sealing surface of the forced closure is very small, so the wear of the sealing surface is also very small. The wear of the sealing surface of the globe valve is mostly caused by the debris in front of the valve core and the sealing surface, or due to the imtightness of the closed state, which causes the high-speed erosion of the medium.