An apparatus comprising a first piston member (22) rotatable about a first rotational axis (30) and a rotor (16) comprising a first chamber (34a) and pivotable about a second rotational axis (32). The first piston member (22) extends across the first chamber (34a). The rotor (16) and first piston member (22) are rotatable around the first rotational axis (30), and the rotor (16) is pivotable about the second rotational axis (32) to permit a relative pivoting motion between the rotor (16) and the first piston member (22) linked to the rotor (16) rotating about the first rotational axis (30).

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.