1979 Ingersol-Rand Patent 4,157,234
Devices of this type, generally referred to as "scroll" pumps, compressors and engines, have two interfitting spiroidal or involute spiral elements of like pitch which are mounted on separate end plates. These spirals are angularly and radially offset to contact one another along at least one pair of line contacts such as between spiral cylinders. The pair of line contacts will lie approximately upon one radius drawn outwardly from the central region of the scrolls. The fluid volume so formed therefore extends all the way around the central region of the scrolls. In certain special cases the pocket or fluid volume will not extend the full 360.degree. but because of special porting arrangements will subtend a smaller angle about the central region of the scrolls. The pockets define fluid volumes which vary with relative orbiting of the spiral centers while maintaining the same relative spiral angular orientation. As the contact lines shift along the scroll surfaces, the !
! pockets thus formed experience a change in volume. The resulting zones of lowest and highest pressures are connected to fluid ports."
