Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A revolving door typically consists of three or four doors that hang on a center shaft and rotate around a vertical axis within a round enclosure. Revolving doors are energy efficient inasmuch as they prevent drafts, thus preventing increases in the heating or cooling required for the building. At the same time, revolving doors allow large numbers of people to pass in and out. Around the center shaft of the revolving door there are usually three or four doors called "wings" or "leaves." Large diameter revolving doors can accommodate strollers and luggage racks. The tallest revolving door currently is approximately 16 feet (4.9 m) high with 4 wings. The glass doors allow people to see and anticipate each other while passing through the door. Manual revolving doors rotate with pushbars causing all wings to rotate. Revolving doors typically have a "speed control" (governor) to prevent people from spinning the doors too fast.

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