RO system startup controller/delay timer

[Sleepydoc]

Whenever I start my RO/DI system, I drain the RO water off before the DI resin until the TDS has dropped, typically 5-10 minutes or so, then I switch it over to run through the resin. Currently I do this by hand but it would be really convenient to have timer and some solenoid valves do it automatically. I know I could do it with an Apex, but that's overkill for this application. Does anyone know of a ready-built setup to do this?

 

[AllSignsPointToFish]

I don't know of any commercial product that does this. However, it seems like you could build one with a digital timer something like this:

And a couple of 12V solenoid valves similar to this:

I tried to find a three-way valve that would work, but I have yet to find one made of plastic. I believe you make this work for under $30 once you throw in a power supply.

 

[Sleepydoc]

Yeah, I'd thought about making my own, possibly just with a 555 timer chip but I'd prefer to have one ready-made. Odd that there isn't anything out there like this