The invention relates to a compressor including: a stationary volute (6) and a moving volute (9) each comprising a plate (7, 11) provided with a scroll (8, 12), said scrolls defining variable-volume compression chambers (13); a separator (16) sealingly mounted to the plate (7) of the stationary volute (6) and defining therewith a first intermediate volume (19); and a delivery chamber (22) defined by the separator and a sealed enclosure. The compressor also includes: a bypass passage arranged to communicate the first intermediate volume (19) with an intermediate compression chamber (13b); a flow passage arranged to communicate the first intermediate volume (19) with the delivery chamber (22); and a bypass valve (34) mounted to the surface of the separator that is facing the delivery chamber, which valve can move between positions for sealing and opening the flow passage.
