(under subclass 284) Device wherein said chamber is formed by a thrust member and an enclosure which together contain a fluid, said enclosure has at least one opening therein for the passage of fluid therefrom, and said thrust member moves past said opening to permit or prevent passage of fluid through the opening.
(1) Note. In this subclass, there is usually an orifice in the piston for flow of a portion of fluid and another orifice in the chamber wall for flow of another portion of fluid. When the piston covers the wall orifice, fluid flows only through the piston orifice and is accordingly restricted to a lesser flow, thus exerting a greater resistance to movement of the piston.
(2) Note. In several devices of this and the indented subclasses the chamber wall that has the orifice(s) comprises a perforated tube (e.g., a piston rod) within a cylinder; thus the wall referred to is an interior wall.
