and cylinder assembly piston 809 performs a reciprocating movement in rotating cylinder or rotor 801 which rotates relative to stationary member 804 stationary member 804 has a curved guide 824 disposed around cylinder 801 the shape of the curved guide 824 protruding from the inner wall of stationary member 804 is indicated by the dotted lines in fig8 a piston 809 is supported by a double t shaped member 825 passing through rotor 801 the t beams 826a and 826b of the double t shaped member 825 support axes 827a to d which carry rollers 828a to d to engage the curved guide 824 the t beams 826a and b upon reciprocating movement of the piston 809 slide within the elongated linear guides 829a and b respectively which are cut into the walls of cylinder 801 piston 809 is sealed towards the working chamber by means of sealing gaskets 810 fig9 a and 9b show an embodiment similar to that of fig8 a and 8b fig9 b being a cross section along the line b b of fig9 a wherein the stationary member 904 has a linear guide disposed therein the linear guide is formed by rollers 930a to d which are supported by.