Originally Posted by typhoon
Ok I know this question has been answered but i can't seem to find it and the tech sheet from DOW does not mention it .
What is the shelf life of a
Don't want to buy old ones .
There is a lot of confusion around this question because a "properly stored" membrane doesn't really have a shelf life. But how do you know if the membrane you buy has been properly stored and how do you properly store one yourself?
Once an RO membrane is allowed to dry out it's done it becomes trash. Secondly storing them at high temperatures can break down the organic film that does the RO magic. Then as a bonus if biological growth happens in the membrane while it's being stored that can kill it. The final item that will kill an RO membrane in storage
is if it's allowed to freeze the ice crystals will tear and rupture the RO membrane and then it's dead. So that's why DOW ships their membranes in a double vacuum bag with sodium metabisulfite preservative inside the bag to keep it moist and to keep biological growth from happening. The storage
temperature for a membrane is 140 degrees Fahrenheit so that's pretty darn hot. So unless it's sat in the back of a truck or the back trunk of a car even an engine
room doesn't really get to 140 degrees. (note: the operating temperature for an RO membrane is 120 degrees but with water flowing through the pressure vessel it's pretty difficult to exceed that temperature during operation)
In my experience the reason people think there's a shelf life with an RO membrane is because it's either allowed to dry out or it's allowed to have biological growth. So the membrane they purchased 3 years ago and had in storage is now dead. So as the end of the day a "newer membrane" does have a less chance of being bad because the time period required to take good care of it is less, so your odds are just better that something bad did not happen to it in storage.
When using an off-the-shelf membrane I really don't see any point in storing a spare aboard your boat. They may cost a little more but they are available anywhere around the world and DHL can typically get one to you in under a week for about a hundred bucks to most places around the world. For Cruisers that insist on carrying a spare membrane I think the best way is to put it inside of a PVC pipe filled with pickling solution with the end caps glued on that way it is protected pretty well and will most likely be brand new when you need it vs dried out and dead.