Re: Pickling watermaker


amelliahona <no_reply@...>
 

Hi All:   The last reply is correct, in that the propylene glycol (NOT to be confused with ethylene glycol) antifreeze solution is too large of a molecule to penetrate the RO (reverse osmosis)  membranes.  

You should NOT raise the pressure in the system while circulating the anti-freeze solution.   Only the water that the propylene glycol is diluted in will penetrate the membrane NOT the antifreeze.

You have to think of your system as two separate loops;  A) the seawater side that includes the sea-chest, sea-water manifold,  low pressure feed pump, pre-filters, high pressure pump, sea-water side of the membranes and housing, control panel plumbing with the pressure knob and associated plumbing, and the brine water rejection plumbing to overboard, and B) the fresh water side of the membranes, the control panel plumbing with the diverter valve, and the lines to the fresh water tank.  

As you probably know I am against using meta-bisulfite for storage.  It is corrosive and damages all metal parts.  When using propylene glycol for winterization (anti-freeze protection) you need to protect both sides of the system.  To protect the sea water side circulate the antifreeze solution thru the system WITHOUT RAISING THE PRESSURE.  After having done that THEN using a syringe or other means of injecting some antifreeze solution flush the fresh water side by disconnecting the fresh water (product water) line at the membranes, allowing the membranes to drain, and then injecting some of the propylene glycol solution into the membrane cavity and thru the product water line.  I would guess that only about 3 or 4 ounces of the antifreeze injected down the product water lines will be adequate as it is a small bore line  and even less will fill the RO membrane center tube (disclaimer I haven't actually winterized my boat but see this:  


Note insert dots and slashes where indicated.

West Marine also has some information on their products for winterizing on their web site.

While there is no way to treat the entire fresh water contents of the membrane cavity (this isn't a loop that you can flush), the center product water tube will drain and you can back flush some antifreeze into that tube.  There isn't a great deal of fresh water volume in there anyway.  So let the fresh water side drain from the membranes, then fill as best you can with concentrated antifreeze then re-connect the already flushed product water tubing to membranes fresh water line.  The bulk of the volume of the cavity is filled with the membranes and the sea water volume.  If what little fresh water there is in the cavity freezes it won't burst or damage the membranes as there is room for expansion provided by the sea-water side which won't freeze. That is my theory at least, as there is no way to circulate propylene glycol thru the fresh water side of the membranes.   

Hope this helps. 

Sincerely, 

Gary S. Silver    s/v Liahona   Amel SM 2000  Hull # 335 
Currently in Puerto Rico at Puerto Del Rey Marina


 

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