Ball valve is a kind of valve with the ball as the closing part, mainly composed of valve body, valve seat, ball, valve rod, handle (or other driving devices, such as electric actuator, pneumatic actuator or hydraulic actuator). It is driven by the valve rod and rotates around the axis of the. It is mainly used to cut off, distribute and change the flow direction of the medium in the pipeline.
There are many kinds of ball valves, including different working principles, using media and application places. Users should select different types of ball valves according to the working conditions. The types of ball valves are classified according to the actual working conditions on site.
1、 Floating ball valve
The ball of the ball valve is floating. Under the medium pressure, the ball 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 transmitted 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 ball of the ball valve 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 availability of sealing, oil sealed ball valve has appeared in recent years. Special lubricating oil is injected between sealing surfaces to form an oil film, which not only enhances the sealing performance, but also reduces the operating torque. It is more suitable for high-pressure and large caliber ball valve.
3、 Elastic ball valve
The ball of the ball valve is elastic. The ball and the seat seal ring are made of metal materials, and the specific pressure of the seal is very large. According to the pressure of the medium itself, it 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 an elastic groove opened 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, and 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.