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From: Larry N. Brown (no email)
Date: Fri Mar 07 2008 - 16:24:44 EST
> REPLY
> Not quite as bad as cold fusion. I lived in a house that was equipped with
> such an RO filter.
> The trouble is, it wasted ten times as much water as it filtered through
> the
> RO membrane.
> Either way you look at it, this is a very wasteful device that uses too
> much
> power and to omuhc water.
> Perhaps the "marine" versions of RO are over priced. But unless you want
> to
> build your own, which is not that dificult, yo upay for the convenience of
> having someone else do it gor you.
> In a house it wastes a lot of water. If the house is on a well the well
> may
> not be capable of delivering so much quantity.
> In a boat you woudl need to generate extra power to drive th epump.
> That being the case, you might as well get the most efficienct pump you
> can
> find to deliver enough potabel water using the least amount of energy.
>
> regards
> Arild
Perhaps I did inject a little hyperbole but to desalinate seawater requires
a great deal of pressure, around 850 PSI depending on the salinity. Here's a
little anecdotal information to establish some data points. In the
Mississippi Sound which varies considerably in salinity from place to place,
it takes 600-850 psi across the membranes to get my normal product water
flow of 40 GPH. In Oak Harbor Marina, just off the Rigolets on Lake
Ponchartrain, it would take 300-500 psi for full flow depending on the
movement of the tide. Here in the Tchefuncte River, totally fresh for all
practical purposes, it takes around 250 psi to get normal flow.
When I finish making RO water, I have a flush switch that opens a solenoid,
allowing RO water from the freshwater tanks to flush the membranes and flow
overboard. Part of my procedure is, when I finish making water, I throw the
tank/test valve to test so when I start the machine anew I can always run
some product water into a cup for a taste test to prevent contamination of m
water supply in the event of a membrane puncture. When I flush the membrane
with the outflow valve wide open, at 0 PSI back pressure, a small stream of
fresh water comes out of the test drain. I'm pumping RO water across the
membranes at little, if any, psi back pressure and yet that water's pure
enough to flow across the membrane.
I bought a commercially produced RO machine with many bells and whistles. I
understood the principles but doubted my capability to fabricate a unit
myself. I was so busy on other projects to get the show on the road, I just
sprung for the store bought one and I'm not dissappointed with it. But, if I
were to get another boat --heaven forefend-- I wouldn't hesitate for a
moment to fabricate one myself with off the shelf parts. It's not rocket
science but it does require some specialized knowledge. If anyone's
interested, I'd be happy to discuss it offline.
Regards,
Larry and Teri
M/V Cigano, 47' Prairie Sundeck Cruiser
Lying: Covington, LA
N 30 26.7
W 90 07.1
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