Based on structure, ball valves are classified into following types:
The ball of floating ball valves is floating. Under the pressure of medium, the ball can displace and compress on the sealing face of exit to ensure the sealing of exit.
Floating ball valves have simple structure and good sealing. However, load of medium bear by ball is transmitted to sealing ring of exit completely. For that, materials of sealing ring must endure the load of medium. Floating ball valves are widely utilized in pipes under low or medium pressure.
The ball of trunnion ball valves is fixed. The ball cannot displace under pressure. Trunnion ball valves have a floating seat. The seat displaces and compresses sealing ring on ball to ensure sealing under the pressure of medium. Generally, the upper and lower axle of ball is equipped with bearing, having low torque. Trunnion ball valves are suitable for high pressure large diameter pipes.
To reduce torque and improve reliability of sealing, oil seal ball valves have come out in recent years. Customized lubricating oil is injected between sealing faces, forming a level of oil slick to enhance sealing and reduce torque. Compared with trunnion ball valves, oil seal ball valves are more suitable for high pressure large diameter pipes.
3. Flexible ball valves
The ball is flexible. Ball and sealing ring of seat are made of metal materials, having high sealing specific pressure. Depending on pressure of medium cannot realize sealing. So the valves must be imposed with external force. Flexible ball valves are applicable for high temperature and high pressure medium.
The lower end of wall inside ball has a elastic groove. Nevertheless, flexible ball valves have flexibility. When closing channel, wedge on stem makes ball roll out and compress on seat to realize sealing. Loosen wedge before rotating ball so that ball can resile. Then, a gap appears between ball and seat to reduce friction on sealing faces and torque.
Based on channel positions, ball valves can be classified into straight through ball valves, three-way ball valves
and right angle ball valves. Three-way ball valves and right angle ball valves are used to distribute medium or change flow direction of medium.
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