Analysis of the characteristics and applications of ball valves
The ball valve is a new type of valve that came out in the 1950s. In just over 30 years, it is one of the valve varieties that have developed rapidly in the past ten years. Especially in developed countries such as the United States, Germany, Japan, France, Italy, Spain, and Britain, the use of ball valves is very extensive, and the variety and quantity of use continue to expand. Life, excellent adjustment performance and multi-function development of a valve, its reliability and other performance indicators have reached a higher level, and have partially replaced gate valves, globe valves, and throttle valves. It has been widely used in many aspects such as aerospace, petrochemical industry, long-distance pipeline, light industry food, construction and so on.
The ball valve 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 of the valve. 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 used as a sphere, and the sphere is rotated 90 degrees around the axis of the valve stem to achieve the purpose of opening and closing. The ball valve is mainly used to cut off, distribute and change the direction of the medium flow in the pipeline. The ball valve designed as a V-shaped opening also has a good flow adjustment function. The ball valve can be closed tightly with only a 90-degree rotation and a small torque. The completely equal internal cavity of the valve provides a straight flow channel with little resistance for the medium. The ball valve is not only simple in structure, good in sealing performance, but also small in size, light in weight, low in material consumption, small in installation size, and small in driving torque within a certain nominal passage range. It is easy to operate, easy to achieve rapid opening and closing, and easy to operate And maintenance, suitable for general working media such as water, solvents, acids and natural gas, but 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.
Why can the ball valve be widely used in many aspects such as aerospace, petrochemical industry, long-distance pipeline, light industry food, construction, etc.? This is because ball valves have many outstanding advantages compared with other valves. The main features of the ball valve are as follows:
1. The ball valve has small fluid resistance and low flow resistance (actually zero):
Ball valves generally have two structures: reduced diameter and non-reduced 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 the channel diameter is equal to the pipe inner diameter, the local resistance loss is only the friction resistance of the pipe of the same length, that is, the flow resistance of this ball valve is small among all valves. In the rocket launch and its test system, the resistance of the pipeline is required to be as small as possible. There are two ways to reduce the resistance of the piping system: one is to reduce the fluid flow rate. For this reason, it is necessary to increase the pipe diameter and valve diameter, which will often have an adverse effect on the economy of the piping system, especially for the low-temperature transportation system ( Liquid hydrogen) is extremely unfavorable; one is to reduce the local resistance of the valve, therefore, the ball valve naturally becomes the best choice.
2. The opening and closing of the ball valve is fast and convenient:
Since the ball valve generally only needs to rotate the handle 90° to complete the fully open or fully closed action, it is easy to achieve rapid opening and closing. It can realize fast opening and closing, and the opening and closing time of some structures is only 0.05-0.1s 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. Good sealing performance of the ball valve:
At present, most of the valve seats of 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 ensure, and the processing accuracy and surface roughness of the sealing surface are not very demanding.
4. Long service life of the ball valve:
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:
①A pair of sealing pair of ball and valve seat will not have troubles such as scratches, sharp wear, etc., and will not get stuck during work (when there is no lubricant), so it can be reliably applied to corrosive media and low boiling point liquids;
②The 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;
③The ball valve with anti-static and fire-resistant structure is suitable for pipelines that transport oil, natural gas, and gas.
