As a side note, if you run your RODI production water line a long distance, those waste water shut off valves don't work so well, they need pressure bladders installed.

I had mine setup this way, it failed to often for me. But I run my output line across my house.

Mark, does your aquasafe have a built in pressure activated valve to shut off waste water production then?

The Aqua-safe units have the valve and just assumed all other units would have one included as well (why I was specific).

As the valve is mounted on the ro/di unit sensing the pressure differance between unit supply and output, can't see why distance would matter (my float is on the end of a probably 20' run).

No, they don't all come with them, I didn't know any of the did come with them.

The RO unit I have came with an electric pump so it can go the distance and has a built in auto shutoff in the unit

?? The feed line can go a long distance, but when the float valve closes, the pressure buildup over the length of the line is not enough to trigger the hydraulic shut off valve. Installing a pressure valve boosts the pressure in the line.

Where does your electric pump come into play in your setup exactly? Are you sure it doesn't boost the psi of your house water pressure for the RODI?

I thing Greg is talking about a booster pump with a pressure switch.

That's it Harvey. I thought that was what we were talking about. Didn't mean to create a thread hijack.
I have my RO running to a res. and from there I have an "Aqua Medic" auto top off unit. I only set it up very recently but so far it works really well.

Thats ok. Your pump is for input pressure, I meant pressure created on the output by a float valve closing. No pump can do that, but pressure bladders like spectra pure sells with their units will.