US Patent 9297381 Switchable single-start or multi-start scroll pump

The present invention is a scroll pump comprising two intermeshing scrolls arranged so that on relative orbital movement of the scrolls gas is pumped from an inlet to an outlet. The scrolls have a plurality of successive scroll wraps I, II, II, IV, V, VI between the inlet and the outlet. There is a single-start condition in which fluid is pumped from the inlet to the outlet along a single flow path extending through each of the scroll wraps in succession and a multi-start condition in which fluid is pumped from the inlet along a plurality of flow paths which extend in parallel through radially adjacent scroll wraps and converge to a single flow path prior to the outlet. A valve arrangement is operable for switching the scroll pump between the single-start and the multi-start conditions.