Revolving door

A revolving door typically consists of three or four doors that hang on a central shaft and rotate around a vertical axis within a cylindrical enclosure. To use a revolving door, a person enters the enclosure between two of the doors and then moves continuously to the desired exit while keeping pace with the doors.

Revolving doors were designed to relieve the immense pressure caused by air rushing through high-rise buildings (referred to as stack effect pressure) while at the same time allowing large numbers of people to pass in and out. They are also energy efficient; they act as an airlock to prevent drafts, decreasing the loss of heating or cooling for the building as compared to a standard door.

Around the central shaft of the revolving door, there are usually three or four panels called wings or leaves. Large diameter revolving doors can accommodate pushchairs and wheeled luggage racks - such large capacity doors are sometimes H-shaped to split the circle into only two (hence larger) parts.

Some revolving door displays incorporate a small glass enclosure, permitting small objects such as sculpture, fashion mannequins, or plants to be displayed to pedestrians passing through. Such enclosures can either be mounted at the central pivot, or attached to the revolving door wings.

The wings of revolving doors usually incorporate glass, to 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.

Automatic revolving doors are powered above/below the central shaft, or along the perimeter. Automatic revolving doors have safety sensors, but there has been at least one fatality recorded.

Skyscraper design requires a means of draft block, such as revolving doors, to prevent the chimney effect of the tall structure from sucking in air at high speed at the base and ejecting it through vents in the roof while the building is being heated, or sucking in air through the vents and ejecting it through the doors while being cooled, both effects due to convection. Modern revolving doors permit the individual doors of the assembly to be unlocked from the central shaft to permit free flowing traffic in both directions. This feature, called breakout or break away, is typically used only during emergencies, or to admit oversize objects. The most effective method for this is the "bookfold" design, which allows all three or four wings to be broken away together. Normally, the revolving door is always closed so that wind and drafts cannot blow into the building, to efficiently minimize heating and air conditioning loads.

In right-hand traffic countries, revolving doors typically revolve counter-clockwise (as seen from above), allowing people to enter and exit only on the right side of the door. In left-hand traffic countries such as Australia and New Zealand, revolving doors revolve clockwise, but door rotations are mixed in Britain. Direction of rotation is often enforced by the door governor mechanism, or by the orientation of the door seal brush (weatherstrips).