RO Membrane Direction

[plabarr]

I'm new to ROs and I have a unit that takes a 4x40 membrane. I got a Dow XLE-4040 membrane and it has a gasket/O-ring on one end but not the other. Could someone tell me which way that o-ring is supposed to face? Feed side or permeate/concentrate side, or maybe it doesn't matter. Thanks for the help!

[bowhunter]

The o-ring is the brine seal and is supposed to face the feed side. If it's installed the other way it may not seal properly.

[plabarr]

Thank you.