Re: [Amel Yacht Owners] Re: Watermaker and transmission fluid

Patrick McAneny

Bill, Thanks for the explanation. If you re pickled after three years and then ran it for a long time to flush it out ,would that get you back to a good set of membranes? Hate to buy new ones ,these were new less than four years ago.

-----Original Message-----
From: greatketch@... [amelyachtowners]
To: amelyachtowners
Sent: Thu, Aug 23, 2018 10:32 am
Subject: Re: [Amel Yacht Owners] Re: Watermaker and transmission fluid

If the membrane is pickled with sodium metabisufite (also called sodium pyrosufite) the issue with long term storage (beyond about 1 year) is not damage to the membranes from the pickling solution, but rather that the pickling solution losses its biostatic properties and the membranes foul from biological growth.  

When dissolved in water sodium metabisufite gradually hydrolyses to release sulfur dioxide leaving a solution of sodium sulfite. Sulfur dioxide is a strong reducing agent, and a very effective microbiocide.  Once all of the sodium metabisulfite hydrolyses, and the resulting sulfur dioxide reacts and dissipates, there is nothing left to protect the membranes from biological growth.  The usual recommendation is that the membranes should be re-pickled after a year to keep them safe.  I would guess that timeframe is actually highly variable depending on initial water quality, pH, bioburden, temperature, and other variables.

This is the same reason that membranes sold "wet" have a relatively short shelf life.  It is not the membranes that "go bad" rather it is the pickling solution.

Bill Kinney
SM160, Harmonie
Annapolis, MD, USA

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