A rotary piston and cylinder device (1) comprising a rotor (2), a stator and a shutter disc (3), the rotor comprising a piston which extends from the rotor into the cylinder space, the rotor and the stator together defining the cylinder space, the shutter disc passing through the cylinder space and forming a partition therein, and the disc comprising a slot (3a) which allows passage of the piston therethrough, the shutter disc comprising a circumferential surface (30) arranged to form a seal with a surface of the rotor, the circumferential surface defining a profile which forms at least one close running line (13b) with said rotor surface, and the at least one close-running line offset from a rotor plane (13) which lies on a radius of the rotor and which includes the axis of rotation of the rotor.

A rotary piston and cylinder device (1) comprising a rotor (2), a stator and a shutter disc (3), the rotor comprising a piston (5) which extends from the rotor into the cylinder space, the rotor and the stator together defining the cylinder space, the shutter disc passing through the cylinder space and forming a partition therein, and the disc comprising a slot (32a) which allows passage of the piston therethrough, and a surface of the rotor and a surface of the stator opposing each other forming a close-running surface pair, and at least one of the surfaces comprising an abradable coating (10) which is provided with a plurality of recess formations, and the recess formations are discontinuous from each other.

A rotor mechanism for use in moving fluid. The rotor mechanism has six rotor units spherically arranged, with at least one rotor unit including a port through it's body. Each rotor has the form of a truncated cone with two symmetric spiral recesses provided on the lateral surface of the rotor which acts to cooperate with the adjacent rotors. Rotation of at least one rotor unit causes rotation of adjacent rotor units which thereby moves fluid without compression between the outside of the mechanism and the port via a central substantially spherical free space cavity formed by the cooperation of inner surfaces of the rotor units. The rotor mechanism is fully submersible.

A rotor for a rotary piston and cylinder device (1), wherein at least part of an outer surface (30) of the rotor (22) is a substantially frusto-conical shaped surface.