A ball valve contains a sphere with a drilled hole or port through the middle of it. When the port is in line with both ends of the valve, flow will occur. When the valve is closed, the hole is perpendicular to the ends of the valve, and flow is blocked. A shut-off is performed by a 90° rotation. Ball valves are the only type of valves which enables the operation of pipe pigging.

 Ball-Valve.pdf

A trunnion ball valve has additional mechanical anchoring of the ball at the top and the bottom, suitable for larger and higher pressure valves (say, above 10 cm and 40 bars).