THE FIRE SERVICE INSTRUCTOR

The Thirteenth Installment of a Treatise to Aid Those Responsible for Training Men in the Fire Service to Develop a Systematic Type of Teaching

Battalion Chief

Chapter IV (Continued)—Helps in Teaching

General Description of Aero System (Continued)

AT each end of the tube there is a diaphragm or small metal box with very thin sides capable of being bulged outward by air pressure. The bulging of the diaphragm closes electrical contacts which operate a transmitter, automatically sending the alarm to the Fire Department. An annunciator indicates the floor or section of the building where the fire originated and a local alarm is sounded on gongs. Each diaphragm frame carries a “vent” which is really a small leak from the tubing to the outer air. The “vent” is the compensating feature of the system. It allows air to pass very slowly into or out of the tubing in order that the inner pressure may be the same as that of the outer atmosphere. Slowly rising temperatures, such as those taking place between night and day or winter and summer or those caused by radiators or other heating appliances, increase the air pressure within the tubing so slowly that it can be relieved through the vents without moving the diaphragms; a fire, however, causes such a rapid increase of pressure that the diaphragms are bulged out, the contacts closed, and the alarm given before the pressure can escape through the vents. The amount of leakage through the vent can be regulated so as to pass a pre-determined amount of air per minute. It is, therefore, easy to adjust the vents so that a fire will give an alarm although a gradual rise of temperature will not do so.

The Aero System operates on the principle of the “rate of temperature rise.” It is not a “fixed point” alarm; that is, it does not necessarily give an alarm of lire because a certain high temperature has been reached. It operates only when the temperature rises rapidly from any previously existing condition, whether that temperature was low or high; it will, therefore, give an alarm from the outbreak of a fire in a boiler room as readily as from a fire in an ice-house.

All parts of the system can be tested for operation as frequently as desired, and no part or device has to be re newed after a fire call has been sent in order to replace the system in service. This applies not only to the electrical parts of the system, but to the tubing circuits as well.

Apparatus

The apparatus installed on the premises consists of one or more Aero tubing circuits each connected to a Detector Unit, one or more manual stations, a control panel with Transmitter and Relay, and Annunciator and iocal Alarm bell. A local Source of electrical energy is also provided together with necessary wire, conduit and miscellaneous fittings.

Aero Tubing

The tubing used in this system is of pure drawn copper with an outside diameter of approximately 1/12″. This tubing is distributed throughout the protected areas so as to insure a prompt alarm on the outbreak of fire at any point. Methods of installation and other structural details are controlled by the rules of the Under writers.

Detector Unit

The tubing circuits terminate in a detector unit. The base of this unit is inches long, 6 1/4 inches wide, and 1 1/4 inches deep, with tapped holes for 1/2-inch conduit both top and bottom. The front cover is a pan 2 inches deep made of pressed steel. The unit has either an enamel or parkerized finish.

One detector unit is required for each tube circuit, both ends of the tubing terminating in the unit. In this are assembled on a small hakelite panel the necessary devices for the operation of the circuit. The devices are: two detector frames in which are set the expansible diaphragms and compensating vents, two annunciatoractuating relays, a test-valve, a test switch and the necessary terminals and wiring.

(To be continued)