Three rotor screw pump with smaller central rotor

摘要

A screw pump including three rotors 12, 14a, 14b each being provided with a generally helical screw thread 20, 20', 26a, 26a' 26b, 26b' with the rotors arranged such that a central rotor 12 is located between the other two outer rotors 14a, 14b and the screw threads mesh with rotation of one rotor causing rotation of the others. The thread 20, 20' of the central rotor is a helical groove extending radially inwardly of the central rotor and the threads of the outer rotors are a helical ridge extending radially outwardly of the rotor and the outer diameter of the central rotor is smaller than the outer diameter of the outer rotors. Provides two fluid delivery chambers between the pump housing and the outer rotors to increase output. Thread pitch and depth may be respectively less than 1.6 to 0.5 and 0.2-0.1 times outer rotor diameter.