I installed a Village Marine/Offshore Marine Little Wonder 250 water
maker a year ago in June. It was supposed to produce 250 GPD, but from
day one I never got that kind of throughput. This translates to about
10.4 GPH and I was only getting between 6.5 (at 12.5V) and 7.2 GPH (at
14.2V) as measured right at the output of the pressure vessel. If you
include the temperature correction factor for 83 F water (0.89), I
really should have been getting 11.7 GPH. To say the least I wasn't
happy.

The entire system has 1/2" ID feeds, 1/4" ID product tubing, a good
boost pump, etc, so there should be no problems with feeds/output. I
was immediately in contact with Village Marine and they requested that I
bring back the motor, membrane and pressure vessel. I was in Guatemala
at the time, and there was no way that I could bring the pressure vessel
back with me, but I brought the membrane and motor back. They replaced
the membrane and brushes on the motor, and then I got to pay for
shipping these items back to Guatemala...$$$$

I reinstalled them when I got back to the boat this cruising season and
there was absolutely no change. Then based upon more e-mail they
discovered that I had the wrong motor. I was supposed to have a blue
1/4 HP motor instead of the black 1/8 HP motor that was on there. So I
hauled the black motor back and brought back the blue motor. More
shipping $$$$ and no change, except that the new motor draws a bit more.

Village Marine has now requested that I bring the entire system back so
that they could test it on their bench. They claim that they've sold
lots of these systems that produce as expected. I'll point out that the
product flow guage that they provide read 0-30 GPH and is very hard to
read at the low end. I replaced it with a 0-12 GPH guage. At this
point I've got the boat in Honduras and there's no easy or inexpensive
way to ship anything to/from the US.

Now I was getting really ****ed, so I started researching how RO systems
work, or shall I say, are supposed to work. An RO membrane is speced to
run at 800 PSI and converts 13-15% of the raw water to product water.
To produce 10.4 GPH, I would need to provide (10.4/0.15)=69 GPH of raw
water at 800 PSI. When I look at my flow gauges, I'm producing 22 GPH
of waste water and 7 GPH of product water, for a total flow of 29 GPH.
This is a far cry from the 69 GPH that need.

It would appear that I'm converting (7/29)=24% of the raw water to
product water, and that this isn't a sufficient flow to scour the salt
crystals from the membrane and this will eventually lead to the membrane
becoming fouled.

I also found a formula for determining how many HP are required to pump
this amount of water. That formula, which is HP=(PSI*GPM)/1460,
translates to 0.63 HP, which is a lot bigger than the 0.25 HP motor that
I have. Working backwards, a 0.25 HP motor should produce 27 GPH, which
is about what I'm getting. At 27 GPH I should only get 4 GPH of
product, but I'm getting up to 7 GPH.

So, my questions are as follows:

1) Are the calculations that I listed above correct?
2) How can I be producing water at the rate that I am?
3)What determines the prodution rate of a membrane assuming that it's at
800 PSI?
4) Does anyone have a Little Wonder system that actually produces at the
speced rate?
5) They claim to need to test the pressure vessle. What could they
possibly be looking for?

-- Geoff