Ball valve is evolved from the plug valve, its opening and closing parts is a ball, the ball rotation 90 degrees around the axis of the stem to achieve the purpose of opening and closing. They are designed to cut off, distribute and change the direction of medium flow in pipelines. The V-shaped ball valve also has a good flow regulation function. Ball valve not only simple in structure, good in sealing performance, And in a certain nominal diameter range, They are small volume, light weight, sample in structure, small installation size, and small driving torque, simple operation, easy to achieve opening and closing, is one of the fastest valve varieties developed in recent decades. Ball valve has a very wide range of USES, variety and quantity continues to expand, to high temperature and high pressure, large diameter, good sealing performance, long service life, good regulation performance, and multifunctional. For their reliability and other performance indicators, they has partially replaced the gate valve, globe valve and throttle valve. With the development of ball valves, they will be used more widely in the foreseeable future, especially in oil and gas pipelines, refinery cracking units and the nuclear industry. In addition, in the industries of the medium and large diameter, Low and medium pressure fields, ball valves will also become one of the leading valve types. Ball valves work by rotating the stem to keep the valve open or blocked. they can be made into a large diameter, still reliable sealing, simple structure, convenient maintenance, sealing surface and valve ball often in the seal state, not easy to be eroded by the medium. Ball valves and plug valves are of the same type, only its closing part is a ball, ball rotating around the center line of the body to open, close a valve. The ball valve in the pipeline is mainly used to cut off, distribution and change the flow direction of the medium. It has the following advantages: 1. The fluid resistance is small, and the resistance coefficient is the same as the pipe section of the same length. 2. Simple structure, small volume and light weight. 3. Compact and reliable, the sealing surface material of the ball valve is widely used in plastic, good sealing, and has been widely used in the vacuum system. 4. Easy operation, fast opening and closing, rotation of 90° from full open to full close, convenient for remote control. 5. Convenient maintenance, simple ball valve structure, sealing ring is generally active, disassembly and replacement are relatively convenient. 6. When fully open or fully closed, the sealing surface of the ball and seat is isolated from the media, which will not cause erosion of the valve sealing surface when passing through. 7. Wide range of applications, sizes from few millimeters to a few meters, from high vacuum to high pressure can be applied. Ball valve has been widely used in petroleum, chemical industry, liquefied gas, water supply and drainage, food, pharmaceutical, power generation, papermaking, urban construction, minerals, boiler steam system, municipal, atomic energy, aviation, rocket and other departments, as well as People’s Daily life. Ball valve is mainly used to put through or block the pipeline medium, especially in the need to quickly open and close the part is better, such as emergency unloading. Because it has the advantages of simple structure, few parts, light weight and good sealing performance. Structure: mainly composed of body, bonnet, sealing seat, ball and stem. The valve ball is the core of the ball valve, the ball is controlled by the rotation of the valve stem to open and close. Ball valves can be divided into floating ball and trunnion ball. According to the different structure of the seal seat is divided into fixed seal seat and movable seal seat. The floating ball with fixed sealing seat is equipped with two fixed sealing seats made of fluorine plastic in the body, and a floating ball made of carbon steel or stainless steel is clamped between the two seats. The ball has a round through hole on the ball. When the ball is opened, the channel is opened; When the stem turns, the hole is perpendicular to the valve’s path, and the pressure of the medium presses the ball against the back seat to ensure valve sealing. The main selection principle of ball valve: 1. For the main line of oil and natural gas transmission, pipelines to be cleaned and buried underground, ball valves of full-size and all-welded structure shall be selected; Buried on the ground, select full size welded or flanged ball valves; Branch pipe, use flange connection, welding connection, full size or reduced size ball valve. 2, The finished oil pipeline and storage equipment, the choice of flange connection of the ball valve. 3, City gas and natural gas pipeline, the choice of flange connection and internal thread connection of the floating ball valve. 4, In the metallurgical system of oxygen pipeline system, it is appropriate to choose after strict degreasing treatment, flange connection of the fixed ball valve. 5, Low temperature medium pipe system and device, it is appropriate to choose a low temperature ball valve with a valve cover. 6. In the pipeline system of catalytic cracking unit of oil refining unit, the lifting rod ball valve can be selected. 7, Chemical system of acid and alkali and other corrosive media device and pipeline system, it is appropriate to choose austenitic stainless steel, PTFE seat sealing ring of all stainless steel ball valve. 8. Metal to metal sealing ball valves can be used in pipeline systems or devices of high-temperature media in metallurgical systems, power systems, petrochemical plants and urban heating systems. 9, The need for flow regulation, can choose worm gear worm transmission, pneumatic or electric with V-shaped opening adjustment ball Valve.