Ball is a sphere with a circular channel for close and open parts, ball rotation with the stem of the valve action to achieve headstock.
Ball valve is one of the fastest growing valve varieties in recent years, has a rotation of 90 degrees.
Ball valve used to be cut off in the main line, distribution and change the direction of the flow medium, it only need to be rotated 90 degrees and a very small torque can close the tight.
Ball valve is most suitable for switch, cut off valve to use, except for V-shaped ball valves. The main feature of the ball valve is compact structure, operation and maintenance easily, suitable for water, solvent, acid and natural gas and other general working media, it’s also suitable for media with harsh working conditions, such as oxygen, hydrogen peroxide, methane and ethylene.
Valve Overview
Fully welded ball valves are used mainly in gas transmission and distribution pipeline (Mid-stream), typical for underground and buried installation.The ball is fixed and the seat rings are floating, free to move along the valve axis.
Side load generated by pressure acting on the ball is absorbed by bearings.
At low pressure the seat sealing acting is achieved by the thrust of the springs acting on the seat. As the pressure increases the fluid pressure pushes the seat rings against the ball, making the sealing more reliable.
A floating ball valve with floating ball(not fixed by a trunnion) inside the valve body, it drifts toward to the downstream side and tightly pushes against the seat under the medium pressure to ensure sealing reliability. The floating ball valve has simple structure, good sealing performance but the seat material is required to withstand the workload since the sealing pressure is bared by the seat ring. Due to unavailability of high performance seat material, floating ball valve is mainly used in middle or low pressure application.
The flow resistance force of ball valve is very small, full bore almost without flow resistance force which make the medium pass through the valve with minimal resistance, therefore, improves the efficiency of the system.
The structure is simple, compare with other types of valves, small volume, light weight, this is not only easy to transport and install, but also reduces manufacturing costs.
Ball valve has excellent sealing performance, most ball valve seats are made of elastic materials such as polytetrafluoroethylene, often referred to as a soft seal. In general, the tightness of the soft seal is easily guaranteed, the machining accuracy and surface roughness of the sealing surface are not very high. In addition, two sealing surfaces of the ball valve are isolated from the medium when open or closed fully, avoid the erosion of the sealing surface by the medium.
Ball valve operation is very simple, just rotate 90 degrees to finish open or close the action, not only speeds up the operation, also easy to control remotely.
The structure is simple, the seal ring is usually active, this makes disassembly and replacement very convenient, simplifies the maintenance process.
Ball valves have a wide range of applications，from 1/2”to 40”，from high vacuum to high pressure environments, can find the suitable ball valve model. In addition, ball valves can also be used in media which contain suspended solid particles.
Ball Valves are mainly divided into two types, i.e. floating ball valve and trunnion ball valve. The former is simple in design and low in price,however, its operation torque is bigger comparing to that of the trunnion ball valve with same diameter. In general, floating ball valve is adopted for valves of small and medium diameter. On the contrary, trunnion ball valve is relatively higher in price, and smaller in operation torque. So valves with bigger diameters are employing generally the design structure of trunnion ball valve. The following table of ball valve tructures relating to each pressure rating is recommended by TEJI to customers for reference when selecting ball valves. The applicable scope of metal to metal sealed ball valve with floating ball is narrower due to bigger operation torque.
Regarding trunnion ball valve, if customers have no special requirement, it is suggested that TEJI make decision based on own processing technique to employ the structure of either two piece or three piece body, Generally, TEJI adopts two piece body design for ball valve≤DN350(NPS14), and three piece design for ball valve≥DN400(NPS16).
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