Pressure Washer Downstream Chemical Injectors Downstream injectors are installed after the pump. In order to function, the pressure must be lowered with the use of either a dual lance and soap nozzle, a variable nozzle, a dual nozzle holder, or an adjustable nozzle holder. Water enters the inlet of the injector and creates a venturi which drops the pressure and suctions the chemical from container. Chemical can be injected either in concentrated form or in diluted form. Chemical can be regulated by turning the dial on the injector or installing a metering device on the chemical line. The injector contains a check valve to prevent water from flowing into the chemical container while in high pressure mode. NOTE: Length of hose will determine ability of injector to work properly. It is recommended to keep hose length at 100 feet or less.