RO DI questions

[mike31154]

Originally Posted by Milad

what should the pressure be after the RO membrane?
also is the RO membrane is the first thing above the 3 things right?
mines go 3 at the bottom, one white thing at top and one clear thing which i think is resin.

Typically you would not monitor the pressure after the RO membrane. The reason to install a pressure gauge before the membrane is to give you a better idea of when your pre filters may be due for a change. This will be indicated by a gradual drop in water pressure as measured just before the membrane. It could also indicate a problem with the membrane itself. It is necessary of course to know what your source pressure is as well, so you can compare the two numbers and make an educated decision as to what may be affecting the performance of your system. Most folks rely on an initial measurement of source pressure and install the gauge before the RO membrane. I chose to install two pressure gauges so I have real time information of both pressure levels whenever the system is running. If your house pressure drops for some reason upstream, it could easily fool you into thinking there's a problem with your RODI system.
EDIT: I've been running this system for over a year now with no filter changes yet. Source water TDS is 210 to 220. Started monitoring the pressures probably 8 months ago. Typical household source pressure is around 85 psi and pressure before the RO membrane 55 psi, giving a pressure differential of 30 psi between source and the membrane. I noticed the poly pre filter getting quite grungy through the clear housing last month and decided to remove it and rinse it off (didn't have a new one on hand). After reinstalling it, I had 86 psi at source and 66 psi at the RO membrane - pressure differential now only 20! Last time I ran the system was just over a week ago, 87 and 60, difference 27. Clearly I need to get a couple of 1 micron poly pre filters and change them more frequently.

As far as how the system is put together, if you're asking about the one in my photo, yes, the RO membrane is mounted horizontally above the three pre filters. I have one poly prefilter and two carbons. The DI resin is in a separate cartridge with bracket at the far left in the photo. I mounted everything to a single 2x4 which is attached to the wall studs. If you're wondering about your own unit, I have no idea since you've provided no photo or manufacturer's info.... although most of them are set up in a similar if not identical manner.