(under the class definition) Apparatus in which the working chamber is formed at least in part by a flexible wall, said wall being progressively distorted by contact with a member external thereto having a surface substantially circumferentially coextensive therewith to expand or contract the working chamber.
(1) Note. For a definition of collapsible wall, see Class 92, Expansible Chamber Devices, subclass 89.
(2) Note. A flexible coating material forming a surface of the working chamber disclosed merely for wear prevention, sealing, protection against corrosiveness, etc., of the coated part is not considered to be a flexible wall for classification here. See this class, subclass 152 and the notes therein for rotary expansible chamber devices having parts either coated with or made of non-metallic material.
