Abstract: Seals for providing sealing contact between the rotary piston and the apexes of the casing of a rotary type combustion engine, compressor, or pump for sealing the several pressure chambers, one from the other or others, during operation. The seals are disposed in radially formed slots at each apex of the housing and are so constructed to permit pressure in the chamber being pressured to be communicated to the rear side of the seal, or the side opposite that which makes sealing contact with the rotary piston, so that such pressure acting on the rear side may assist the spring normally acting against the same side in forcing the seal against the rotary piston with greater pressure and thereby provide a better sealing effect.