T&T: Fw: Fw: $150 Reverse Osmosis System

[Larry N. Brown]

> 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