Tue Apr 29, 2014 2:28 am
This has been discussed before, but here we go. Supercharged sirens do not require as much air pressure (P.S.I.) as much as they require air volume (C.F.M.). Thunderbolt blowers only supply 6 or 7 P.S.I. A person blowing hard exceeds that, but does not have the needed volume of air required to supercharge a large siren. A slight amount of back pressure is required to create the air pulse, but a consistently large flow of air is required to sustain the air pulse. As the chopper closes off the stator port the roots blower is able to build up some back pressure (6-7 P.S.I.). As the chopper turns and opens the stator port this slight back pressure creates the the initial air pulse heard, but the consistent large air flow sustains the air pulse until the cycle starts over.
What you have found is nothing more than a fast moving fan. Fans do not create much back pressure. Once there is a restriction on the output end of the fan the air stops moving forward and just moves around within the fan housing. A roots blower on the other hand has two rotors with a close tolerance to the blower housing. This close tolerance does not allow the air to just move around in the housing once there is a restriction. The air must move forward out of the blower wether there is a restriction at the output or not. This is the reason there is a relief valve on the output end of the blower.
Owner of a Federal Electric Model 2, Federal Sign and Signal SD-10, Federal Sign and Signal 1000(T) and a H.O.R. Si-Rex 7:10 Omnidirectional