In addition to water pressure, LP’s are sensitive to back
pressure. Back pressure is the amount of pressure
required down stream of the proportioner to discharge
the total foam solution flow. This will include the pressure
required at the inlet to the discharge device(s), elevation
head and line losses. The total allowable back
pressure
on the discharge side of the LP can not exceed
65% of the water inlet pressure. If back pressure
exceeds
65%, the LP may not pick-up foam concentrate
or the solution may be lean.