Pneumatic Sirens

Pneumatic sirens are relatively rare devices, which are still present mainly in Germany, and earlier could be found in Switzerland. These devices take adventage from pneumatic solutions, thanks to which they are capable of achieving a very high sound volume for the cost of being (mostly) considerably large, heavy and bulky devices, which are difficult to maintain. Pneumatic sirens are not being used in Czechia, and there is no evidence that might indicate their installation in the past. However, such devices were actively tested in Czechia sometime in the 20th century, although most likely proscribed for use.

Principle of Function

Pneumatic sirens work similarly to mechanical sirens. The sound is generated in the siren's head, when the air is "chopped" between air ports of a swiftly spinning rotor and a stator, which is stationary. The "chops" then result in strong bursts of air, of which the wavelenght transforms into a mechanical sound. The main difference between mechanical and pneumatic sirens is that the air is not supplied by a centrifugial force (sucked into the rotor by the stator's air intakes) but is instead delievered to the head via pipeline from a pressurized air tank or a compressor, located under the siren's pole. This solution significantly allows for a greater volume and performance, and another adventage also lies in the fact that an source of pressurized air is always available.