I'm trying to understand why you and @ smart n cleen are trying to design a completely new class of battery sprayers. If sprayer is going to be in the van and something goes wrong with it ( and eventually it will, e.g clogged filter) than you have to run back to the van and fix it, instead working on hydro force directly. I see playing with your battery sprayers in summer time, but doing this in winter is just plain ineffective. Your thin plastic line will freeze in matter of seconds sitting on the frozen ground. Same thing can happen to a Neptune , or any solution line if you're not moving quick enough. Don't forget, once warm, hot water starts running trough line, you're golden and worry free. If you think that atomization from your battery operated sprayer will be lesser, it all depends what spray pattern are you using at the tip of spray wand
( hopefully not a mist nozzle). Why not adjust pressure regulator on TM or porty to a desired pressure and proceed with injection sprayer. You'll get right ( or more accurate dilution) . IMO what's important about playin down prespray is a technique. 12"-15" off of the floor and pointing wand straight down, not swinging it like a tennis rocket, will get you satisfactory results.
I would like to see you making some innovative moves, not going back in time.
I don't mean all that in derogatory way, I'm just saying that prevac, prespray, crb-ing or whatever means of getting carpet clean are being used should be one smooth process and playing with a plastic/ vinyl tubing with no flexibility ( not in freezing temps) ain't going to cut it.