A method and apparatus are disclosed for operating an air supply system for a glass sheet quench including a D.C. drive system of a variable speed blower operated on a duty cycle. A quench cycle and a cooling cycle are carried out in the quench. In the preferred embodiment shown for thin glass (i.e. glass which is 5 mm or less in thickness) the drive system is sized to the RMS requirements of the complete cycle to minimize the initial and operating costs, size and power requirements of the D.C. drive system.
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