(under the class definition) Apparatus in which a cylinder and a rotating working member of substantially like axial extent have interfitting internal and external helical surfaces of unlike pitch, rotation of the working member causing relative gyratory movement between the cylinder and the working member to thereby expand and contact the working chamber.
(1) Note. Such devices wherein the cylinder is the working member are considered proper for classification here.
(2) Note. Included herein are devices in which the cylinder is made of a tubular material, helical surfaces thereon being formed by the helical surfaces of the working member pressing thereagainst.
