1. From the structure
The one-piece ball valve is integrated by the inside of the ball, PTFE ring and lock nut. The caliber of the ball is slightly smaller than that of the pipe diameter. It is similar to the wide
ball valve.
The two-piece ball valve is composed of two parts. The sealing effect is better than the one-piece ball valve. The caliber of the ball is the same with that of the pipe, which is easier to disassemble than the one-piece ball valve.
The three-piece ball valve is composed of three parts: both sides of the valve cover and the middle valve body. The three-piece ball valve is different from the two-piece ball valve and the one-piece ball valve is convenient to disassemble and maintain.
2. From the pressure
The pressure of three-piece ball valves is much higher than that of one-piece and two-piece ball valves. The main three-piece ball valve outside is fixed by four bolts, which plays a good fastening role. The cast valve body can be pressed up to 1,000psi≈6.9MPa. Higher pressures require a forged body.
3. According to the structure forms, ball valves can be divided into the following types:
Floating ball valves:
The ball body of the ball valve is floating. Under the action of medium pressure, the ball can have a certain displacement and tight pressure on the sealing surface of the outlet end. It can ensure the outlet end sealing. The structure of the floating ball valve is simple. The sealing is good, but the working medium of the bearing load of the ball all passes to the export seal ring. Therefore, it is necessary to consider whether the sealing ring material can withstand the working load of the sphere medium or not. This structure is widely used in middle and low pressure ball valves.
Fixed ball valves:
The ball body of the ball valve is fixed. The pressure does not move. Fixed ball valves are all with floating seat. It is moved by the medium pressure so that the sealing ring is pressed on the ball in order to ensure the sealing. Bearings are usually installed on the upper and lower shafts of the ball, and the operation torque is small. It suitable for high-pressure and large-diameter valves. In order to reduce the operating torque of ball valves and increase the reliability of the seal, there is an oil seal ball valve. The special lubricating oil is injected between the sealing surfaces to form a layer of oil film. In order to enhance the sealing and reduce the operating torque, the high-pressure large-caliber ball valve is more suitable.
Elastic ball valves:
The ball body of the ball valves is elastic. The ball body and valve seat sealing rings are made of metal materials. The sealing pressure is very large. It relies on the pressure of the medium itself which has not reached the requirements of sealing, and the external force must be applied. This valve is suitable for high temperature and high pressure media. The elastic sphere is at the lower end of the inner wall of the sphere to open an elastic groove and obtain elasticity. When closing the aisle, use the stem wedge to open the ball and seal the seat. Loosen the wedge head before turning the ball. Then, the ball will then return to its original shape so that there is a small gap between the ball and the seat, which can reduce sealing surface friction and operating torque.
According to its channel position, ball valves can be divided into straight-through type, three-way type and right-angle type. The latter two ball valves are used to distribute media and change the flow direction of media.
