Mixing up membrane gpd ratings

[ADK_XJ]

I have a 4 housing setup with 150 gpd membranes that I've run in series for the last two seasons but just received another set of 4 RO housings (no membrane) and all the fittings to plumb into the system.

My question is: can I use a lower GPD membrane to save some cash or should I really be matching to the 150 gpd membranes I have to preserve efficiency? There's quite a cost jump from 100 to 150.

I guess a second question would be, now that I have so many membranes should I considering running one set in parallel and then into the next set in parallel to get better flow? I have 150-200 gpd rated pump, is that too much for the little guy?

Thanks, all!

[carls47807]

What model pump are you using?

As a general rule for these small systems, you don't want to run more than 4x more membrane capacity than the rating of your pump (a 200gpd pump should be able to run 800gpd in membranes). Beyond that, you will need unnecessary restriction in order to keep pressure up (restriction that does not produce more permeate), and decrease the flow which could cause membranes to foul. Running 2 sets of 4 in parallel might be beneficial only because 8 in a row gets complicated.

Depending on your pump specs, I think 6 would be your max. You can mix and match membranes. Running them first as opposed to last doesn't theoretically matter.