Characteristics and Selection of Ball Valves

The Ball Valve is evolved from a cock, and its opening and closing part is a sphere, which rotates 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 flow direction of medium in the pipeline. The ball valve with V-shaped opening also has good flow regulation function.

The ball valve is not only simple in structure and good in sealing performance, but also small in size, light in weight, less in material consumption, small in installation size, small in driving torque, easy to operate and easy to realize quick opening and closing, so it is one of the fastest developing valve varieties in recent ten years. Especially in industrial developed countries such as America, Japan, Germany, France, Italy, West and Britain, ball valves are widely used, and their varieties and quantities continue to expand, and they are developing in the direction of high temperature, high pressure, large warp, high sealing, long life, excellent regulating performance and multi-function of one valve. Their reliability and other performance indexes have reached a high level, and they have partially replaced Gate Valves, globe valves and throttle valves. With the technical progress of ball valves, they will be widely used in the foreseeable short term, especially in oil and gas pipelines, oil refining cracking units and nuclear industry. In addition, in other industries, the ball valve will become one of the leading valve types in the fields of medium and large caliber and medium and low pressure.

Ball Valve

The working principle of ball valve is to make the valve open or closed by rotating the valve stem. The ball valve switch is light and small in size, can be made into a large diameter, has reliable sealing, simple structure and convenient maintenance, and the sealing surface and spherical surface are always in a closed state, which is not easy to be eroded by media, and is widely used in various industries.

Ball valve and plug valve belong to the same type of valve, only its closing part is a ball, and the ball rotates around the center line of the valve body to open and close.

Ball valves are mainly used to cut off, distribute and change the flow direction of medium in pipelines. Ball valve is a new type of valve widely used in recent years, which has the following advantages:

1. The fluid resistance is small, and its resistance coefficient is equal to the pipe section with the same length.

2. Simple structure, small volume and light weight.

3. Tight and reliable. At present, the sealing surface material of ball valve is widely made of plastic with good sealing performance, and has also been widely used in vacuum system.

4. Convenient operation, quick opening and closing, only 90 rotation from full opening to full closing, which is convenient for remote control.

5. The maintenance is convenient, the ball valve structure is simple, the sealing ring is generally movable, and the disassembly and replacement are convenient.

6. When the valve is fully open or closed, the sealing surfaces of the ball and valve seat are isolated from the medium, and when the medium passes, it will not cause erosion of the valve sealing surface.

7. Wide application range, from small diameter to several millimeters to several meters, from high vacuum to high pressure.

Ball valves have been widely used in petroleum, chemical industry, liquefied gas, water supply and drainage, food, pharmaceutical, power generation, paper making, urban construction, mineral, boiler steam system, municipal, atomic energy, aviation, rocket and other departments, as well as people's daily life.

The ball valve is mainly used to connect or block the pipeline medium, especially in the parts requiring quick opening and closing, such as emergency unloading. Because of its simple structure, few parts, light weight and good sealing performance, it has been widely used. Structure: It is mainly composed of valve body, valve cover, sealing valve seat, ball and valve stem. The ball with hole is the core of the ball valve, and the ball is controlled to open and close by the rotation of the valve stem. Rotation is the whole switch. Ball valves can be divided into floating ball valves and fixed ball valves. The characteristic of floating ball valve is that the ball can float freely. According to the different structure of seal seat, it can be divided into fixed seal seat and movable seal seat. The floating ball valve with fixed sealing valve seat has the structure as shown in the figure. Two fixed sealing valve seats made of fluoroplastic are installed in the valve body, and a floating ball made of carbon steel or stainless steel is clamped between the two seats. The ball has a circular through hole, and the channel opens after opening; When the valve stem rotates, the ball hole is perpendicular to the passage of the valve, and the ball is pressed against the back valve seat by the pressure of the medium to ensure the sealing of the valve.

Main selection principles of ball valves:

1. For the main pipeline of oil and natural gas transmission, which needs to be cleaned and buried underground, the ball valve with full diameter and full welded structure shall be selected; For ball valves buried on the ground, choose full diameter welded connection or flange connection; Branch pipe, choose flange connection, welding connection, full diameter or reduced diameter ball valve.

2. Flanged Ball Valves shall be used for the transportation pipeline and storage equipment of the finished oil.

3. Floating ball valves with flange connection and internal thread connection shall be used in the pipeline of city gas and natural gas.

4. In the oxygen pipeline system of metallurgical system, the fixed ball valve with strict degreasing treatment and flange connection should be selected.

5. Low temperature ball valves with valve covers should be selected for piping systems and devices of low temperature medium.

6. Lifting rod type ball valve can be used in the pipeline system of catalytic cracking unit of oil refining unit.

7. All-stainless steel ball valves made of austenitic stainless steel and with PTFE as valve seat sealing ring should be selected for the devices and piping systems with corrosive media such as acid and alkali in chemical system.

8. Metal-to-metal sealed ball valves can be selected for piping systems or devices of high-temperature media in metallurgical systems, power systems, petrochemical devices and urban heating systems.

9. When flow adjustment is needed, the adjusting ball valve with V-shaped opening driven by worm gear and worm, pneumatic or electric can be selected.