The use of piecewise forms for the numerical representation of shape

A valve in which a valve member is mounted for rotary valving motion within a valve casing and an actuator in which at least one pair of expansible bellows engaging opposite sides of a vane and acting in opposition one to the other give rise to rotary motion. The bellows preferably are free from any direct fixation to the vane or the like, and have a particular configuration as described.