Abstract: A lightweight, heavy duty, large volume centrifugal compressor for use in mechanical vapor compression systems, especially water vapor compression systems in heat pump installations, said compressor comprising a shaft driven propeller-like rotary member consisting of a frusto-conical hub and a plurality of curved blades made of a lightweight material, each being secured to said hub along a longitudinal curved line and radially extending therefrom; each pair of adjacent blades being interconnected by a bridging membrane member of a lightweight material curvingly extending from the roots of the leading edges of said adjacent blades to the tips of the rear edges of the blades; said rotary member being encompassed within a closely fitting shroud, so that curved vapor flow channels are defined between each said pair of blades, their associated membrane member, and the shroud.