the piston assemblies are carried by a common shaft and displaced 90 degrees apart each piston assembly includes two pistons the pistons have their working end surfaces 180 degrees of rotation apart the rotor shaft is hollow along a portion of its length the hollow portion of the shaft delivers fluid under pressure from an external source through channels within the pistons to fluid troughs in the circumferential surfaces of the annular chambers additional channels in the annular chambers and housing provide fluid under pressure to actuate shuttle valves at specific rotation locations of the pistons in each chamber each chamber includes side wall vents for exhausting spent working fluid a screen is positioned vertically between the adjacent vents to cause condensate to be directed to a collection sump by gravity application_number US 10440187 A description referring now to the various drawing figures fig1 depicts a partial cutaway showing of the rotary external combustion engine 10 of the present invention the engine housing includes a working fluid input end plate 12 an output end plate 14 a bottom or floor surface 18 side walls 17 see the various other figures and a cover or top surface 16 within the housing is a pair of annular chambers 20 and 22 the inside surfaces of the annular chambers are enclosed by mirror image annular chamber end plates 23 and 24 a partially tubular or hollow rotor shaft 25 passes through the engine 10 longitudinally.