Sail Switches
A sail switch consists of a steel or polyester film sail mounted on a switching device (see Figure 6-43). The combined unit is mounted so that the sail is located in an air duct. When the air velocity increases, the switch makes an electrical circuit. Figure 6-44 illustrates the location of the sail switch in a gas control circuit.
Sail switches are used in forced warm-air heating systems, in air- conditioning systems, and with gas-fired unit heaters. Some sail switches are designed to provide on-off control of electronic air cleaners, odor-control systems, humidifiers, and other equipment that is energized when the fan is operating. In these applications,
the sail switch completes a power circuit to auxiliary equipment, which can be wired independently of the blower motor. Sail switches are also used in electric heating systems to provide mini- mum airflow.