Re: Duo 60 Watermaker



I assume you have tested the water right of of the watermaker itself and it shows the same salt content?  If not, then it is a tank problem...

I wish I had a simple answer for you...  There are two likely causes for high solids content in the permeate from an RO unit: a bad seal or a bad membrane.

The first thing I would try to do is to isolate the problem to one of the two pressure vessels. Try disconnecting the product water lines from the two membrane housings, and collect permeate from each of them separately.  
I'll bet you find one very much saltier than the other, and we would then know where the problem is.  In the unlikely case BOTH are equally bad, you might have gotten a bad batch of membranes, but that seems unlikely.  Could also have been a technique problem in installation of the membranes if Dessalator's instructions were not closely followed.

Now comes the hard part...

Seal? or Membrane?

Since we have (hopefully) now shown that one combination of membrane and pressure vessel is the source of the problem, we need to figure out is it seal, or membrane. With the membrane in the housing, I know of no test that would give a differential diagnosis between those.  If we remove the membrane, we can test it separately.  It is a bit involved, but not too bad...  Here is a description of the process:

The alternative to that complex test is to just replace the bad membrane with its seals.  But before you do, check the housing VERY carefully for any scratches or roughness in the places where the seals seat.  When you install a new membrane, be sure to follow the instructions from Dessalator exactly.

Bill Kinney
SM#160, Harmonie
Nanny Cay, Tortola, BVI.

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