3.6.5 Butterfly and ball valves
The seal of a butterfly valve is mounted on the circumferences of the valve plate. The plate revolves around an axis, which runs transversely through the circular valve housing. The valve plate remains in the valve opening. The valve has a short design and a low flow resistance, as the gate releases almost the entire cross section.
Ball valves are extremely robust valves with free passage and vacuums to about 1 · 10-5 hPa. A ball with a hole through it is rotatably supported and sealed on both sides by means of universal ball joints (usually made of PTFE), which also have holes through them. When the hole is in the direction of the flow, the entire cross section is released. It should be noted that ball valves contain an enclosed volume when closed.
In the 3-way design, the ball bore is in the form of an “L” or “T”. Due to the size of the bore, the three ports may overlap when switching.