Variable in-line inductors are used to mix foam concentrate with water when the foam concentrate is supplied from a tank at atmospheric pressure. This in-line inductor has a better tolerance to back pressure and better foam concentrate suction than a standard in-line inductor. The HP- Z 200 inductors are connected to the water line. They can be placed far from the foam branchpipe, as they can accommodate up to 5 bar pressure loss in the hose.