Abstract: A combination double screw rotor assembly includes a first screw rotor and a second screw rotor arranged in parallel in a casing, the first screw rotor and the second screw rotor each having a low pressure screw rotor element, a high pressure screw rotor element, and a spiral thread formed of a first spiral thread segment at the high pressure screw rotor element and a second spiral thread segment at the low pressure screw rotor element, the first spiral thread segment having an uniform short pitch, the second spiral thread segment having an uniform long pitch, the upper spiral thread segment and second spiral thread segment of the first screw rotor being respectively meshed with the first spiral thread segment and second spiral thread segment of the second screw rotor.

Abstract: An asymmetric double screw rotor assembly includes two asymmetric screw rotors respectively revolvably meshed together in a casing having an inlet and an outlet, the spiral threads of the screw rotors defining an uniform pitch, the outer diameter of the first screw rotor and the inner root diameter of the second rotor being uniform, the inner root diameter of the first screw rotor gradually increased from the inlet of the casing toward the outlet, the outer diameter of the second screw rotor gradually reduced from the inlet of the casing toward the outlet. Upon respective rotary motion of the screw rotors, the volume of the respective air chambers gradually reduces from the inlet of the casing toward the outlet.

Abstract: A double screw rotor assembly includes two screw rotors meshed in a bushing inside a casing. The threads of the screw rotors have a uniform pitch, and define with the bushing a plurality of air chambers in the pitch. The volumes of the air chambers reduce gradually from the inlet toward the output due to the reduce of tooth high so that the outer diameter defined by the tooth tip of the thread of each screw rotor has the shape of an invertedly disposed cone. Adjustable spring means is provided to impart an axial spring force to the bushing relative to the casing, guide means is provided to guide axial movement of the bushing relative to the casing, and a O-ring is disposed between the top wall of the bushing and the casing. Adjusting the pre-loading of the spring means controls the dimension of the clearance between the inside wall of the bushing and the tooth tip of the thread of each screw rotor.

Abstract: A double screw rotor assembly includes two screw rotors meshed in a bushing inside a casing. The threads of the screw rotors have a constant pitch, and define with the bushing a plurality of air chambers in the pitch. The volumes of the air chambers reduce gradually from the inlet toward the outlet due to reduced tooth height so that the outer diameter defined by the tooth tip of the thread of each screw rotor has the shape of an invertedly disposed cone. An electric driving device is controlled to move the bushing axially in the casing relative to the screw rotors in adjusting the clearance between the inside wall of the bushing and the tooth tip of the thread of each screw rotor, so as to minimize the consumption of starting power and facilitate stable running of the screw rotors, Further, a O-ring is provided at the top wall of the busing and pressed on the casing to keep an airtight status, so as to improve the working efficiency.