can be separated in the exhaust chamber and can flow to the sump chamber wherefrom the lubricating oil can flow back to the rotor chamber through a bore in a rotor drive shaft which communicates with the sump chamber through an orifice application_number US 86677778 A description a casing 1 of the compressor has a cylinder block 2 therein at one end and a rotor chamber 3 is formed in the casing at its other end a cylinder head 4 is secured to one end of the casing 1 and a suction valve 18 and a valve plate 6 are interposed between the cylinder head 4 and the top face of the cylinder block 2 the cylinder head has an air inlet chamber 7 in a central portion on the inner face of the cylinder head and an exhaust chamber 8 around the air inlet chamber the cylinder head has an air inlet silencer chamber 9 at one lateral side portion at the outer face of the cylinder head the cylinder head has an exhaust silencer chamber 10 in an upper portion of the other lateral side of the cylinder head and a sump chamber 12 in the lower portion the chamber 10 is separated from chamber 12 by a separator 11 an orifice 11a.