The difference between triple-offset and “quadruple-offset”shut-off butterfly valves

Triple-offset shut-off butterfly valves are considered state of the art. Compared to other butterfly valve types, such as centric or double-offset designs, they open and close without any friction. A few years ago even alleged “quadruple-offset” shut-off butterfly valves were introduced. Even the experts could easily comprehend the fourth offsetity feature. When looking closely at the geometry it becomes obvious that doubt in the fourth offsetity is not unfounded.