Thunderbolt Siren Restoration-Blower Page

Thunderbolt Siren Restoration Blower Thunderbolt Siren Restoration Main Siren Chopper Chopper Housing Rotator Blower Siren Controls Sirens Main Page Civil Defense Museum Main		The Thunderbolt siren uses a blower unit consisting of a roots blower and a large electric motor to pump 250 cubic feet of air per minute at 6.5 psi. through the chopper. This gives the siren it's high sound output by "supercharging" the siren unit at the top of the pole. Here is the blower frame with the motor, on the left, and roots blower, on the right. The blower air pipe comes out of the bottom of the blower and goes out in between the rails at the right end of the unit. The round object, on top of the air pipe just to the right of the the blower is the blower pressure relief valve. This valve releases air pressure if the chopper is not running and has the opening in the siren stator blocked, or if the air flow is blocked for some other reason. The valve has weights that stack on top of it to hold the valve down until the pressure exceeds 6.5 psi. When the pressure exceeds this amount the valve lifts up and releases the excess pressure while the blower is running. This way the blower is protected. This motor and blower are not the original units that were with this siren. The original roots blower, pictured below, was completely rusted inside. This motor and blower came from a mid-1970s vintage Thunderbolt so it has the smaller type roots blower. The motor is a 7.5 hp 3 phase unit that checked good when I had it tested at a motor shop. I mounted the blower skid on a set of heavy casters to make the siren easy to move around. It actually worked very well. The siren was easier to move around on the casters than my big Matco toolbox. Click Photo To See Larger. This is the original blower that was with the siren. This thing is a solid chunk of pig iron! This blower was completely siezed with rust from water sitting in the blower. Later model Thunderbolts have smaller blowers that weigh about 1/2 of what this thing weighs. I think the blowers were changed in the early 1970s but I'm not sure. Here is a view of the back side of the blower unit. You can see the air pipe and pressure relief valve to the left.I didn't repaint the blower frame. I just gave it the WD-40 and rag treatment. Here is the siren assembled without the blower cover on. I could run the rotator in this arrangement because the weight of the blower and motor was more than enough to counteract the weight of the horn as it rotates.

The Thunderbolt siren uses a blower unit consisting of a roots blower and a large electric motor to pump 250 cubic feet of air per minute at 6.5 psi. through the chopper. This gives the siren it's high sound output by "supercharging" the siren unit at the top of the pole.