John,
My American fire truck uses what they called a Barton Vacuum Primer, mounted on the fire wall. It's a sorta kidney-shaped beast, one larger float chamber beneath a second, smaller chamber. It's plumbed at the top from manifold vacuum, then to the top side of the pump.
Pull the lever, and vacuum pulls water through the hard suction, into the pump, then into the lower primer chamber. When the float raises enough, a drain opens and the water escapes. If, for some reason, the lower float does not operate, the water goes into the upper chamber, and raises the back-up float, which vents the suction, thereby protecting the engine from ingesting water.
I've always thought these vacuum primers were elegant in their simplicity, not much to malfuntion, and they don't freeze, since they're in the engine compartment. They turn up occasionally on "The Bay", often sold with the fire pump thrown in! ;-)
Other trucks use a large electric motor turning a positive displacement pump to draw the water. Works fine as well. Speaking of which, what happened to your truck's original primer? Had to have one when in service.
Gotta agree with you, drafting is a blast.
-Michael
