Controlled suction unloading in a scroll compressor

A positive displacement scroll type fluid compressor comprising

• a. two generally parallel plates, the facing surface of each having an involute wrap element attached thereon in fixed angular, intermeshed relationship with the wrap element of the other, said wrap elements of each defining a radially inner and a radially outer flank surface of similar spiral shape about an axis, contacting flank surfaces of the intermeshed wrap elements and plates defining pockets of fluid;
• b. a drive shaft rotatably driven about a longitudinal axis by a prime mover, and operatively connected to one of the two parallel plates in driving relationship, the other plate being fixed so that said one plate is caused to orbit relative to the fixed plate when the drive shaft rotates;
• c. a perimeter wrap attached to the fixed plate on the same surface as its involute wrap element, extending from that involute wrap element in a lobular shape which encloses the wrap element on the orbiting plate in circumvallate sealing relationship;
• d. a first and a second fluid inlet, disposed generally diametrically opposite each other in the fixed plate adjacent its periphery, and in fluid communication with one or more of the fluid pockets as they are formed;
• e. a compliant sealing member disposed adjacent the perimeter wrap, extending between it and the outer flank surface of the orbiting plate involute wrap element and between the parallel plates in sealing relationship, said member being operative to prevent fluid flow between the first and second fluid inlets;
• and
• f. valve means for controlling fluid flow to at least one of the first and second fluid inlets and thereby operative to modulate the capacity of the compressor.