The ball valve is the valve that uses a sphere with a circular through hole as the opening and closing part, and the sphere rotates with the valve stem to realize the opening and closing action. The ball valve evolved from the plug valve, also known as the spherical plug valve. The opening and closing part of the ball valve is a sphere, and the sphere rotates 90° around the axis of the valve stem to achieve the purpose of opening and closing. Compared with other valves, the ball valves have many outstanding advantages. The main characteristics are as follows:
1. The ball valve has small fluid resistance and the lowest flow resistance (actually zero)
The ball valves generally have two structures: reduced and non-reduced diameter channels. Regardless of the structure, the flow resistance coefficient of the ball valve is relatively small. Especially the so-called full-flow type, that is, the ball valve that does not reduce the diameter, because its channel diameter is equal to the inner diameter of the pipeline, the local resistance loss is only the friction resistance of the pipeline of the same length, that is, the flow resistance of this kind of the ball valve is the smallest among all valves. In the rocket launch and its test system, the resistance of the pipeline is required to be as small as possible.
2. The opening and closing of the ball valve is fast and convenient.
Since generally we only need to rotate the handle of the ball valve 90°to complete the fully open or fully closed action, it is easy to achieve rapid opening and closing. The opening and closing time of some structures is only 0.05 to 0.1s, so as to ensure that it can be used in the automation system of the test bench. When opening and closing the valve quickly, there is no shock in operation.
3. The ball valve has good sealing performance.
At present, most of the valve seats of the ball valves are made of elastic materials such as polytetrafluoroethylene, and the sealing pair composed of metal and non-metal materials is usually called a soft seal. Generally speaking, the tightness of the soft seal is easy to guarantee, and the processing accuracy and surface roughness of the sealing surface are not very demanding.
4. The ball valve has a long service life.
Because PTFE has good self-lubricating properties, the friction and wear with the ball is small, and due to the improvement of the ball processing technology, the roughness is reduced, thereby increasing the service life of the ball valve.
5. The high reliability of the ball valve is mainly due to:
(1) The sealing pair of the ball and the valve seat will not suffer from scratches, sharp wear and other failures, and will not get stuck during work (when there is no lubricant), so it can be reliably used in corrosive media and low-boiling liquids;
(2) The built-in valve stem structure eliminates the potential accident risk that the valve stem may fly out due to the loosening of the packing gland under the action of fluid pressure;
(3) The ball valve with anti-static and fire-resistant structure is suitable for pipelines that transport oil, natural gas, and coal gas.
6. Flat and smooth passages in the valve body are more suitable for conveying viscous fluids, slurries, and solid particles.
7. Because it will not get stuck during work (when there is no lubricant), it can be reliably used in corrosive media and low-boiling liquids.
8. The ball-type closing piece of the ball valve can be automatically positioned in position and can withstand the high pressure difference when it is closed.
9. In a large pressure and temperature range, it can achieve complete two-way sealing.
10. During fully open and fully closed action, the sealing surface of the ball and the valve seat is isolated from the medium, so the medium passing through the valve at high speed will not cause erosion of the sealing surface.
11. With compact structure and light weight, it can be considered as the most reasonable valve structure for cryogenic media systems.
12. The ball valve body is symmetrical, especially the welded valve body structure, which can well withstand the stress from the pipeline.