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Structure and Features of Ball Valves

Basic structure and sealing principle of
ball valves

Valves in which a ball rotates on a valve stem as a shaft to control the fluid.
As shown in Fig. 1, the flow path has the same shape as the piping, and there are few elements that give resistance to the fluid, so the structure has extremely low pressure loss when fully opened.


Fig. 2: Floating ball type	Fig. 3: Fixed ball type
The floating ball type has a non-fixed connecting structure of the ball and stem so that the ball moves in the flow direction when fully closed as shown in Fig. 2. With this structure, a self-sealing effect can be expected by pressing the balls against the secondary seat due to the differential pressure when the valve is fully closed. It is mainly used for low pressure (up to JIS20K, CL300) and small bore size (up to DN200).	The fixed ball type has a structure in which the upper and lower portion of the ball are supported and fixed by the stem and trunnion as shown in Fig. 3. With this structure, the fluid is closed using the spring force at the back of the seat and the pressure on the primary side applied to the back of the seat when fully closed. Therefore, the seal is on the primary side, and it is characterized by less fluctuation of operating torque against fluctuation of flow pressure. It is mainly used for high pressure (JIS30K, CL600 or higher) and large bore size (DN250 or higher).

Features of ball valves

①Easy operation of fully open and closed

Opening and closing operations can be performed quickly by turning the stem 90 degrees.
In addition, the open/close state of the valve is clearly indicated by the position of the lever handle, so it has excellent visibility.

②Excellent sealing

PTFE and other plastic materials are used for the valve seat, which makes it easier to stop the fluid with excellent sealing performance.

③Extremely low pressure loss

Since its flow path has the same shape as the piping and there are few elements that give resistance to the fluid, the structure has an extremely low pressure loss when fully opened.