Double screw rotor assembly having means to automatically adjust the clearance by pressure difference

A double screw rotor assembly comprising:

• a casing, said casing comprising an inside wall defining a receiving chamber, an inlet and an outlet respectively disposed in communication with the receiving chamber of said casing;
• a bushing mounted in the receiving chamber inside said casing and moved axially along the inside wall of said casing, said bushing having a double loop-like cross section and comprising an inside wall defining a receiving chamber and an outside wall fitting the inside wall of said casing;
• guide means to guide axial movement of said bushing relative to said casing;
• an O-ring mounted on said bushing at a top side and facing said casing;
• two screw rotors meshed together and mounted in the receiving chamber inside said bushing, said screw rotors each comprising at least one spiral thread of a constant pitch, said at least one spiral thread each comprising a tooth tip, two side walls, and a root of tooth, said tooth tip of said at least one spiral thread of each of said screw rotors defines an outer diameter having the shape of an invertedly disposed cone;
• and
• pre-loading adjustable spring means mounted between said bushing and said casing and imparting an axial spring force to said bushing relative to said casing, wherein said adjustable spring means pushes said bushing away from said casing to increase the gap between the inside wall of said bushing and the tooth tip of each spiral thread of said screw rotors before rotation of said screw rotors, and said bushing is forced by a pressure difference between said inlet and said outlet to conquer the axial spring force from said adjustable spring means and to force said O-ring against said casing after rotation of said screw rotors, thereby causing the gap between the inside wall of said bushing and the tooth tip of each spiral thread of said screw rotors to be gradually reduced.