PDA

View Full Version : 75gpd vs 100gpd RO


bboshart
02/25/2008, 04:47 PM
I purchased a RO/DI unit mail order. I chose the specific unit because it had a 75gpd Dow filmtec membrane which I understand is highly rated. When my unit arrived there was no membrane. I called the store and they said they would send one as soon as possible. It arrived today but is a "Waterite Black Max 100gpd". The enclosed packing slip said "free upgrade to 100 gpd". I don't what to do?? I don't need 100, 75 would be sufficient. Is there a big difference in efficiency between 75 and 100. Does Dow make this membrane? What would you do?

AZDesertRat
02/25/2008, 05:14 PM
Never heard of that brand. Its either a repackaged membrane from Dow, GE or Applied membranes or it could be a Chinese or Taiwanese knockoff. I would not use it without more information. The 100 GPD Dow is the worst possible membrane you could get while the 75 is the industry standard. I would call them and get more info on manufacturer, rejection rates and GPD at what pressure.

bboshart
02/25/2008, 05:30 PM
They (the membrane) have a website http://www.waterite.com

If I'm using a 100 instead of 75, do I need a different restricter? Restricters need to be matched to the membrane?

tankman10000
02/25/2008, 05:36 PM
i would make them send me what i bought in the first place

AZDesertRat
02/25/2008, 09:57 PM
They appear to be a true RO at 96-98% rejection rate but are 100 GPD at 60 psi. The 75 GPD Dow is 75 GPD at 50 psi, 90 GPD at 60 psi and 100 GPD at 65 psi so it is very similar to the 75 GPD Dow.

bboshart
02/26/2008, 05:27 AM
I emailed my vendor and this is the reply:

"When I spoke with our purchaser he provided me with a little insight. The 75GPD units have a 100GPD membrane in them but use a 75GPD flow restrictor. It is this difference in flow rate that provides you with the slightly higher rejection rate."

Sounds plausible, so I'm happy with what I have. Either way I'll have 0 TDS water, perhaps my DI resin will not last as long.

AZDesertRat
02/26/2008, 01:40 PM
I would calculate the waste ratio to ensure it is sufficient. Sounds like what they are doing is wasting less to build up a higher pressure to drive it through the membrane. The disadvantage to this is you may not get sufficient flushing of the membrane causing it to fail prematurely. You always want 4:1 waste ratio when possible to keep it well flushed. If you water conditions are near pristine 3:1 may suffice but for most of us who exceed a TDS or 250 or so it is not enough.
I don't like their answer, they still did not answer the question as to who manufacturers the membrane.

bboshart
02/26/2008, 02:37 PM
I guess the proof will be in the performance. Once my TDS meter arrives, I'll get it going. I do have a flush kit (restrictor by-pass) installed. Thanks for the replies.

AZDesertRat
02/26/2008, 03:24 PM
Still test your waste ratio. Many times vendors include a fixed orfice flow restrictor that may or may not be right for your pressure and temperature. Manually flushing the membrane does not replace having the correct waste flows.