Blower Motors

The Thunderbolt siren was an electro-mechanical warning siren once manufactured in the United States by Federal Signal Corporation. The Thunderbolt siren consists of three motors. more...

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The blower motor is housed inside a large rectangular "motor box" typically found at the base of the siren (or in some installations on a wooden platform mounted half way up the utility pole, other methods include mounting a long wooden platform halfway up between two poles.). This motor is connected to a standpipe which blows or pumps air up to the "chopper" motor. As the chopper spins, the air forced into it escapes out of rapidly opening and closing holes, creating the siren's sound or "roar". Finally, a rotator motor turns the siren's projector horn 360 degrees when in operation. The Thunderbolt could be shipped in single or three phase power and could either be installed pole mounted or roof mounted.

Thunderbolt history

The Thunderbolt was first produced by Federal Enterprises (now Federal Signal Corporation) in 1952. There were three models manufactured:

Model 1000, a single tone siren which generated 127 dB of sound (measured from 100 feet away from the siren);; Model 1000T, a dual tone version which generated 126 dB at 100 feet;; Model 1003, a dual tone version with the added capability of producing a Hi-Lo "fire" signal. This model also generated 126 dB at 100 feet.;

The dual tone Thunderbolt 1000T/1003 models have often been described by siren enthusiasts and casual listeners alike as having the most eerie and ominous sound due to its very distinctive dual tone that is usually sounded in a minor third. On all Thunderbolt models, the pitch of the siren was adjustable; most often, no two Thunderbolt sirens in the same community sounded the same (unless adjusted for consistency). Some lower pitched 1000T's have been described as sounding like a very loud dial tone. On single tone 1000 models, the sound from the blower motor can be more noticeable giving this version somewhat of a bass-like background sound, setting it apart from the sound of other single toned siren models. The rotator motor/projector horn had three speed settings — 2, 4, or 8 RPM.

Typically, these sirens were/are often seen painted bright yellow. This has more recently come to be known as "Civil Defense Yellow", although on occasion, one might find a Thunderbolt painted in other various colors to meet the community's needs. Very early examples of the siren could be observed with the projector horn painted "zebra striped" black and yellow, or red and white (most often the former). The projector horns on early models were fitted with two sets of metal grilles welded to the front opening of the horn. This was to exclude debris and birds from building nests inside. By the late 1950s, the manufacturer removed the grille design in favor of a protective black mesh screen.

Read more at Wikipedia.org