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A scroll compressor is a rotating displacement compressor, i.e. it compresses a specific amount of air in an ever decreasing volume. The compressor element consists of a fixed spiral in an element housing and a motor powered eccentric, moveable spiral. The spirals are mounted with 180° phase displacement to form air pockets with a varying volume. This provides the elements with radial stability. Leakage is minimised as the pressure difference in the air pockets is less that the pressure difference between the inlet and the outlet. The moving spiral is driven by a short stroke crankshaft and runs eccentrically around the centre of the fixed spiral. The intake is situated at the top of the element housing. When the moving spiral runs clockwise air is drawn in, and is captured in one of the air pockets and compressed variably in towards the centre where the outlet and a non-return valve are situated. The compression cycle is in progress for 2.5 turns, which virtually gives constant and pulsating free air flow. The process is relatively silent and vibration free, as the element has hardly any torque variation compared to, e.g. a piston compressor.