Like I said, Rosa has a bug in the pressure calculations. I think they are
doing it in pascals and screwing up the conversion to PSI.

Also like I said, although you have to have bought a "5HP" compressor with a
9 amp motor to appreciate it, the R/O salesmen have taken lessons from the
air compressor people.

You also have to take into account that the membrane makers have a different
motive from the R/O system builders. Membranes work over a fairly wide
ratio of product to brine. The membrane makers use conservative figures so
the membranes will last a long time and you will buy more membranes to meet
your product requirement. The system builders use the higher limits so they
can quote the best production with the cheapest cost of production. As long
as the membrane last longer than the warranty period they are happy.

I have not been able to find any hard numbers on the Village marine products
but from what you have said it looks like they are holding the system
pressure above the required osmotic pressure and reducing the flow. That
will increase the recovery rate but it also shortens time between descaling.
There is just no other way to do it with a single SW30-2540 and an under
powered pump.

I probably won't see any VM techs until the Annapolis show if then but when
I do you have given me some new arrows for my quiver. I will shoot a few at
them and see how the dance goes.
--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Geoff Schultz" wrote in message
6...

Thanks for all of the information regarding formula constants. It helps
a lot to understand the calculations. Now that I understand them better
I feel like I'm looping back to prior questions.

Using 1 HP = 746 watts I looked at Village Marine's current offerings
and computed production statistics for their systems using a genereous
13.2V.

Their Littlewonder 160 system draws 13.7A which translates to 0.24HP
which should pump 0.42 GPM and produce 91 GPD at 800 PSI and a 15%
recovery rate. In order for it to produce 160 GPD, you need to
overdrive the membrane at 24% instead of the speced 13%. The same
numbers hold (actually increase to 25% and 28%) for their 200 GPD and
300 GPD systems.

A key point that I seem to be missing is how to overdrive the membrane.
I can only assume that it's by increasing the pressure supplied to it.
The production rates are speced at 800 PSI, so I assume that by
increasing the pressure that the product flow rate increases.

The things that really confuses me is the pressures reported by ROSA.
ROSA reports feed pressures that are typically in the 25-150 PSI range.
What are these pressures? Are these above 800 PSI, or what? I just
don't understand what they're relative to as they clearly aren't
absolute pressures.

-- Geoff