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Book - School of Science and Technology

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Types <strong>of</strong> refrigeration plant 539SuctionRotorsTwin helical rotorsFigure 19.6 Screw compressorUnloaderpistonSlidevalveDischargemachines to a cooling capacity in excess <strong>of</strong> 4.5 MW <strong>and</strong> <strong>of</strong>fers the advantages <strong>of</strong> minimumvibration <strong>and</strong> low noise level. Open, hermetic or semi-hermetic machines areavailable, depending on the size <strong>and</strong> the manufacturer. In the smaller sizes, screw compressorsare manufactured as sealed units with capacity control by a simple slide valvemechanism down to 25% <strong>of</strong> full load.CondenserCoolingwater inCoolingwater outCompressor<strong>and</strong> motorFloatvalveChilledwater outEvaporatorWater inFigure 19.7 Centrifugal system

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