Structure, characteristics, advantages and classification of ball valve

The ball valve is evolved from the plug valve, which has the same 90 degree rotation lifting action. The ball valve can be closed tightly only by 90 degree rotation and small rotation torque. The completely equal inner cavity of the valve body provides a small resistance and straight passage for the medium.

The main features of ball valve are compact structure, easy operation and maintenance, suitable for general working media such as water, solvent, acid and natural gas, and also suitable for media with poor working conditions, such as oxygen, hydrogen peroxide, methane and ethylene. The ball valve body can be integral or combined.

1. The closing part of the ball valve is a ball. It is a kind of valve that the ball rotates around the center line of the valve body to open and close. Ball valve is mainly used to cut off, distribute and change the flow direction of medium in pipeline. Ball valve is a new type of valve widely used in recent years. It has many advantages, as follows.

2. It has the lowest flow resistance (actually 0); it can be used in corrosive medium and low boiling point liquid because it will not stick when working (when there is no lubricant).

3. In a large range of pressure and temperature, it can achieve complete sealing;.

4. It can realize fast opening and closing, and the opening and closing time of some structures is only 0.05 ~ 0.1s, so as to ensure that it can be used in the automation system of the test bench. When the valve is opened and closed quickly, there is no impact during operation, and the spherical closing part can be automatically positioned at the boundary position;

5. When fully open and fully closed, the sealing surface of the ball and valve seat is isolated from the medium, so the medium passing through the valve at high speed will not cause the erosion of the sealing surface.

6. It has compact structure and light weight, so it can be considered as the most reasonable valve structure for low-temperature medium system; the valve body is symmetrical, especially the welded valve body structure, which can well bear the pressure from the pipeline; the closure part can bear the high-pressure difference when closing.

The ball valve with fully welded valve body can be directly buried in the ground, so that the internal parts of the valve will not be eroded, and the maximum service life can reach 30 years. It is the most ideal valve for oil and gas pipelines.

Ball valve can be divided into:

1. Floating ball valve

The sphere is floating. Under the action of medium pressure, the sphere can produce a certain displacement and press tightly on the sealing surface of the outlet end to ensure the sealing of the outlet end. The structure of floating ball valve is simple and its sealing performance is good, but the load of working medium borne by the ball is all transferred to the outlet sealing ring, so it is necessary to consider whether the sealing ring material can withstand the working load of the ball medium. This structure is widely used in medium and low pressure ball valves.

2. Fixed ball valve

The sphere is fixed and does not move under pressure. Fixed ball valves are equipped with floating seats. Under the pressure of medium, the seats move to make the sealing ring tightly press on the ball to ensure the sealing. Bearings are usually installed on the upper and lower shafts of the ball, with small operating torque, suitable for high-pressure and large-diameter valves. In order to reduce the operating torque of ball valve and increase the reliability of sealing, oil sealed ball valve has appeared in recent years. Special lubricating oil is injected between the sealing surfaces to form an oil film, which not only enhances the sealing performance, but also reduces the operating torque, and is more suitable for high-pressure and large caliber ball valve.

3. Elastic ball valve

The sphere is elastic. Both the ball and the seat seal ring are made of metal materials. The specific pressure of the seal is very large. The pressure of the medium itself can not meet the requirements of the seal, so an external force must be applied. This valve is suitable for high temperature and high pressure medium. The elastic sphere is to open an elastic groove at the lower end of the inner wall of the sphere to obtain elasticity. When the channel is closed, the wedge-shaped head of the valve rod is used to make the ball expand and compress with the valve seat to achieve sealing. Before rotating the ball, first loosen the wedge-shaped head, then the ball will return to its original shape, so that there is a small gap between the ball and the valve seat, which can reduce the friction and operating torque of the sealing surface.

The ball valve can be divided into straight through type, three-way type and right angle type according to its channel position. The latter two ball valves are used to distribute media and change the flow direction of media.

Its many characteristics make the ball valve widely used in petroleum, chemical industry, power generation, papermaking, atomic energy, aviation, rocket and other departments, as well as people's daily life.