A frequently asked question concerning Firovac is "On your vac/pumpers is it possible to fill the tank at a draft site while at the same time as pumping into another truck?"
The answer is: We do not set our units up to do that for the following reason,
Although it could possibly work for a short period of time, eventually the vacuum pump will overcome the fire pump and it will cavitate the fire pump. A fire pump functions at 15-16 inches of mercury and the vacuum pump goes up to 25-27 inches of mercury. Cavitation of a fire pump will destroy the impeller.
Furthermore, a more efficient way to supply water is to discharge it into a drop tank from which the pumper can fill. Pumping directly into another truck provides no water reserve beyond the booster tank. A drop tank is worth another tank in the system as it extends the water reserve.
The picture below shows Firovac drafting from a creek and discharging into a drop tank. The pumper then drafts from the drop tank to fight the fire.