The subject invention described herein is directed to an improved fluid powered system for dispensing a selectively variable proportion of additives into a primary fluid supply line such as is commonly encountered in the firefight industry where it is desirable to proportion foam concentrates into a water line. The subject invention features a water driven motor that is integral to a variable displacement additive pump. A proportioning adjustment allows the solution % to be adjusted. Once set, the additive percent varies in direct proportion to the water flow rate in order to maintain a nearly constant solution percentage over a broad flow range.