Join Date: Sep 2004
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SD is correct about seeking manufacturer advice. I offer the comments below as a "generic approach". I developed it because I have a desal system that's engineered from generic components and the "manufacturer - assembler" of the system was located in a warm climate and chose not to deal with the subject in the Xerox-ed owner's manual I have.
I winterize the system by first "pickeling" the membrane and then removing the pressure vessel with the membrane and biocide inside. I carefully cap the fittings to keep the biocide in the pressure vessel to keep the biocide from spilling out and then take it home -- storing it horizontally in a warm space. The key is not to let any part of the membrane dry out during the winter.
Winterizing the rest of the unit is pretty simple. The filters are removed and drained (new filters are installed on recommissioning) and the pumps and lines are winterized with non-toxic antifreeze. I make sure that on recommissioning all the anitfreeze is flushed from the system before installing the pressure vessel and membrane. This can make a mess, especially when you flush the HP pump, so you want to make preparations to contain the flushing water. To flush the system on recommissioning, use clean seawater if you can. If not, use distilled water. Don't use tap water as it may contain chlorine which will harm the membrane.
It's my understanding that the biocides in the membrane will hold up for only six months, so it's possible that the membrane might need cleaning when you recommission the system.
I've found keeping up with the desal maintenance to be too much of a hassle unless we're in a live-aboard cruising mode where we are not often at a dock and/or water is expensive. When we're just doing seasonal cruising in NE, water is free and not hard to find, so I keep the system off line. This means that I may need to replace the membrane when we go cruising again, but that's a price to pay for not having to recommission, maintain and decommission the system every summer.