The ball valve evolved from the plug valve, and it has the same 90-degree rotation lifting action. The ball valve can be closed tightly with only a 90-degree rotation operation and a very small torque. The completely equal inner cavity of the valve body provides a very small resistance and straight flow channel for the medium.
The main characteristics of the ball valve are its compact structure, easy operation and maintenance, suitable for general working media such as water, solvents, acids and natural gas, and also suitable for media with harsh working conditions, such as oxygen, hydrogen peroxide, methane and ethylene. The ball valve body can be integral or combined.
The closing part of the ball valve is a sphere, which is a valve that rotates around the center line of the valve body to achieve opening and closing. The ball valve is mainly used in the pipeline to cut off, distribute and change the flow direction of the medium. The ball valve is a new type of valve that has been widely used in recent years.
Ball valves can be divided into the following types according to their structure:
1. Floating ball valve
The ball is floating. Under the pressure of the medium, the ball can produce a certain displacement and press tightly on the sealing surface of the outlet to ensure the sealing of the outlet.
The floating ball valve has a simple structure and good sealing performance, but the load of the working medium borne by the ball is all transmitted to the outlet sealing ring. Therefore, 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 ball is fixed and does not move after being pressurized. Fixed ball valves are all equipped with floating valve seats. After being pressurized by the medium, the valve seat moves, so that the sealing ring is pressed tightly on the ball to ensure 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 the ball valve and increase the reliability of the seal, an oil-sealed ball valve has appeared in recent years. It not only injects special lubricating oil between the sealing surfaces to form an oil film, but also enhances the sealing performance and reduces the operating torque. It is more suitable for high-pressure and large-diameter ball valves.
3. Elastic ball valve
The ball is elastic. The ball and the valve seat seal ring are made of metal materials. The sealing pressure ratio is very large. The pressure of the medium itself cannot meet the sealing requirements, and external force must be applied. This valve is suitable for high-temperature and high-pressure media.
The elastic ball is elastic by opening an elastic groove at the lower end of the inner wall of the ball. When closing the channel, the wedge head of the valve stem is used to expand the ball and press it against the valve seat to achieve sealing. Before turning the ball, loosen the wedge head, and the ball will return to its original shape, so that a small gap appears between the ball and the valve seat, which can reduce the friction of the sealing surface and the operating torque.