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Old 01/11/2008, 01:34 PM
jdieck jdieck is offline
Flea Slide
Join Date: Dec 2002
Location: Naperville IL
Posts: 12,458
Originally posted by AZDesertRat
The waste is still 4:1 at the final point of waste. I make 240 GPD, I waste 240x4 or 960 gallons, its not less. its still 4:1 of the total production. Membranes will not last as long without doing , Dow and Spectrapure don't stay in business by not bench testing things like this for years and years. Short term it will work but eventually it will catch up to you guaranteed.
I do not know how you have your system connected or if you are using individual restrictors for each membrane or if you adjusted a single overall restrictor to give you 4:1 overall but in my system that is not the case.
The overall total waste is not 4:1 it is 4:2 (Look at the mass balance in the diagram above) which is equivalent to 2:1 (Two gallons of waste for each gallon of product for the combined system)
Despite this lower overall ratio the flow used to flush membrane 1 is 5 times its product which is better than what the specification of 4:1 calls for. The flow used to flush membrane 2 is 4 times it's product volume which for membrane two will make it 4:1.

By the way I do not claim to have designed this myself, it is a design I got from Scott's (from Spectra) published diagrams.

I remember you saying back then when I first presented this about two years ago about eventually catching up "guaranteed" and that no one has tested it long term.
Well here we are again but it has not caught up yet after 5 years for membrane one and 4 or so years for membrane two (which I installed after I had the system in operation for about a year).

The thing I really do not understand is were do you get that the flushing ratio of each membrane has been reduced when in reality has been increased for membrane 1. The only difference is that membrane two is getting water with 20% higher ppm but still well within the membrane's specifications specially if the TDS of the tap water is relatively low.
Did I write what I wrote? What the heck am I talking about! Well..... Nevermind.

Last edited by jdieck; 01/11/2008 at 01:44 PM.