I'm just making up a softwash system for a job next week, I'm more worried about too much flow, if the WFP hose I'm going to use restricts the flow slightly I think that will be a good thing. I'm using a small 50psi pump to pull the solution out of a water tank to feed a WFP brush and as telescopic lance.
Will your hose have a trapped pressure? I don't think the flow is what might cause the problem it's the pressure the pump is pushing out