For Foam Supplied Pump
The foam pump should be a rotary or gear type. A variable speed hydraulic motor, a direct drive auxiliary engine, or a power take-off from the truck transmission should drive the pump.
The drive system for the foam concentrate pump should be independent of the drive system for the water pump, such that the foam pump may be run without the water pump.
The foam pump should be suitable for pumping foam concentrate at the full range of temperatures experienced at the location.
The foam concentrate pump maximum discharge pressure should be 300 psig as limited by the pump pressure relief valve to ensure proper foam proportioning over the full operational range of the water pump.
The foam concentrate pump should provide sufficient concentrate when the water pump is running at minimum capacity with the maximum allowable suction pressure.
To protect the pump, a pressure relief valve, sized for pump blocked outlet, should be provided on the discharge side, bypassing back to the pump suction.
A valve blow-off strainer should be installed on the foam pump suction to protect this circuit from scale and foreign particles.