Mechanical operation for pivoted and projected ventilators is achieved with a horizontal torsion shaft actuated by an endless hand chain or by motor power. Arms attached to the torsion shaft open and close the vents.
Two common types of operating arms are the lever and the rack and pinion (Fig. 11.59). The lever is used for manual operation of small groups of pivoted vents where rapid opening is desirable. The rack and pinion is used for longer runs of vents and can be motor powered or manually operated. The opening and closing by rack and pinion are slower than by lever arm.
Usually one operating arm is furnished for each vent less than 4 ft wide and two arms for each vent 4 ft or more wide. Mechanical operators should be installed by the window manufacturer before glazing of the windows.
Continuous top-hung windows are mechanically controlled by rack-and-pinion or tension-type operators (Fig. 11.59).
DOORS
The purpose of doors is to close openings that are needed in walls and partitions for access to building interior spaces, when closing is required to prevent trespass by unauthorized persons, to provide privacy, to protect against weather, drafts, and noise, and to act as a barrier to fire and smoke. Many types of doors are available for this. They may be hinged on top or sides to swing open and shut, they may slide horizontally or vertically, or they may revolve about a vertical axis in the center of the opening.
A large variety of materials also is available for door construction. Wood, metal, glass, plastics, and combinations of these materials with each other and with other materials, in the form of sandwich panels, are in common use.
Selection of a type of door and door material depends as much on other factors as on the primary function of serving as a barrier. Cost, psychological effect, fire resistance, architectural harmony, and ornamental considerations are but a few of the factors that must be taken into account.
Doors may be classified as ordinary or special purpose. Ordinary doors are those used to protect openings up to about 12 ft high or wide. Often, such doors are available in stock or standard sizes. Larger doors may be considered special purpose, because they are generally custom designed and built and require specially designed framing.
In either case, a door system consists of a door proper, hardware for control of door movement (Arts. 11.65 to 11.67), a door frame around the wall opening to support the door and trim the opening, and structural framing, such as a lintel, to support the wall and other building components directly over the opening.
