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

"Geoff Schultz" wrote in message
6...
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?

1) Those are the same formulas I am working from. Pretty standard. You
really need .6HP to supply 1.1 GPM @ 850PSI. You can't get more than about
28 GPH @800PIS out of 1/4HP
2) Sounds like you are overdriving the membranes and they are going to
scale up a lot faster. I ran the numbers you gave through Rosa, Dow's
design program. Even at the designed 10 GPH product @ 15% the concentrate
flow is marginal at best. At half that supply rate concentrate flow is way
low.
3) Salinity of the water, temperature, condition of the membranes,
configuration of the membranes, pressure and rate of feed water. Are the
membranes plumbed in series or parallel? Is the pressure between 800 and
850PSI? Are you pulling from a brackish river outflow or open seawater?
4) Built my own
5) I have no idea.

--
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

"Glenn Ashmore" wrote in
news:IkAye.148973$sy6.17500@lakeread04:


"Geoff Schultz" wrote in message
6...
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?

1) Those are the same formulas I am working from. Pretty standard.
You really need .6HP to supply 1.1 GPM @ 850PSI. You can't get more
than about 28 GPH @800PIS out of 1/4HP
2) Sounds like you are overdriving the membranes and they are going
to scale up a lot faster. I ran the numbers you gave through Rosa,
Dow's design program. Even at the designed 10 GPH product @ 15% the
concentrate flow is marginal at best. At half that supply rate
concentrate flow is way low.
3) Salinity of the water, temperature, condition of the membranes,
configuration of the membranes, pressure and rate of feed water. Are
the membranes plumbed in series or parallel? Is the pressure between
800 and 850PSI? Are you pulling from a brackish river outflow or open
seawater?
4) Built my own
5) I have no idea.

Glen,

I've used ROSA also and came up with the basically the same numbers that
I do by hand. I'm running a single 2.5"x40" SW30-2540 membrane and am
pulling in normal seawater at 83F and running it at 825 PSI.

I must admit that one thing thta I've never understood about ROSA is how
to specify the input pressure to the membrane. If I specify a feed
pressure of 825 PSI it shows 100% of the feed water turning into
permeate (product water). I just leave it 0 and it caculates things as
expected at 800 PSI. If I specify 25 PSI for the feed pressure, it
calculates a recovery rate of 44%, which is way high. Any idea on how
to specify an feed pressure of 825 PSI?

Back to one of my main questions. I've never quite understood how RO
membranes work. How is it that the production rate of the membrane
varies based upon the quantity of the water passing over it? The
pressure is the same. Is it the scouring effect of the flowing
raw/waste water?

-- Geoff

I think there is a bug in Rosa when it comes to feed pressure. It comes up
with pressures that exactly 1/10th of what I come up with by hand.

Actually the flow rate of the feed water only indirectly effects net product
at a given pressure. What it does do is change the ratio of product to
brine. As the salt content of the brine goes up the required osmotic
pressure goes up. If the system pressure remains the same the product goes
down. Conversely, the more feed water you supply the salt concentration
goes down so the required osmotic pressure goes down. If the system
pressure remains the same product goes up.

You can increase the product up to 25% or so just by increasing system
pressure a bit and cutting back the feed rate but at the price of
considerably shorter membrane life. The membranes are not just super fine
filters. Quantum theory is still black magic to my Newtonian brain so I
don't fully understand it but basically the atoms in the membrane material
have an electrical effect on the salt ions (all salt ions, not just sodium
chloride) that forces them away from the membrane surface. Ions also repel
each other so as the number of salt ions increase they are forced closer to
the membrane and scaling increases.

--
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...
"Glenn Ashmore" wrote in
news:IkAye.148973$sy6.17500@lakeread04:


"Geoff Schultz" wrote in message
6...
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?

1) Those are the same formulas I am working from. Pretty standard.
You really need .6HP to supply 1.1 GPM @ 850PSI. You can't get more
than about 28 GPH @800PIS out of 1/4HP
2) Sounds like you are overdriving the membranes and they are going
to scale up a lot faster. I ran the numbers you gave through Rosa,
Dow's design program. Even at the designed 10 GPH product @ 15% the
concentrate flow is marginal at best. At half that supply rate
concentrate flow is way low.
3) Salinity of the water, temperature, condition of the membranes,
configuration of the membranes, pressure and rate of feed water. Are
the membranes plumbed in series or parallel? Is the pressure between
800 and 850PSI? Are you pulling from a brackish river outflow or open
seawater?
4) Built my own
5) I have no idea.

Glen,

I've used ROSA also and came up with the basically the same numbers that
I do by hand. I'm running a single 2.5"x40" SW30-2540 membrane and am
pulling in normal seawater at 83F and running it at 825 PSI.

I must admit that one thing thta I've never understood about ROSA is how
to specify the input pressure to the membrane. If I specify a feed
pressure of 825 PSI it shows 100% of the feed water turning into
permeate (product water). I just leave it 0 and it caculates things as
expected at 800 PSI. If I specify 25 PSI for the feed pressure, it
calculates a recovery rate of 44%, which is way high. Any idea on how
to specify an feed pressure of 825 PSI?

Back to one of my main questions. I've never quite understood how RO
membranes work. How is it that the production rate of the membrane
varies based upon the quantity of the water passing over it? The
pressure is the same. Is it the scouring effect of the flowing
raw/waste water?

-- Geoff

I still have more questions about RO systems. Manufactures quote their
system production rates in GPD and Amps. I compare them by calculating
product Gallons per Amp-hour, and the rates seem to be all over the board.
For example, Village Marine systems utilize about 2 AH per gallon for their
Little Wonder Systems. HRO systems are 4+ AH per gallon.

The manufacture's publications make you believe that their systems have
become more efficient through their pump and motor technology. Is there
really that much difference in technology? Some vendors claim to have an
energy recovery system, but I don't understand what this is or how it
works. It certainly doesn't seem to apply to basic systems that I'm
looking at.

Any insights into this?

-- Geoff

I think the RO salesmen have taken lessons form the air compressor people.
Gallons per hour is a lot more useful but gallons per day sounds better.
There are a lot of ways to play with the numbers. The basic physics is hard
to get around but there are a lot of "soft numbers" they can work with.
The simplest way is to overdrive the membranes and change the owner's manual
to require more frequent maintenance. Ideally a membrane should be driven
at 14-15% product but they will work all the way up to 30% or more given the
right conditions. They just won't last as long. Parallel membranes are
more efficient than series membranes because both membranes see the same
salt concentration but they require more flow and therefore more expensive
pumps. Some of the more expensive systems use a multi-stage membrane
arrangement that makes the system more complex but can be 10-20% more
efficient. Also the higher the capacity the more efficient they can be.

The only real way to really get more product for less energy is with a
pressure recovery device. On big commercial systems this is usually an
impulse impeller driven by the discharged brine. They are big heavy,
expensive and don't really do much good until you are in the 50-100 GPM feed
range. The Clark pump as used by Spectra and a few others is the most
efficient and the only recovery device that is practical on a boat..

In most systems the energy in the high pressure brine is lost when it passes
through the pressure regulator. The energy stored as pressure is converted
to velocity and is discharged overboard.. That is about 70% of the total
energy used by the system. The Clark pump is a variation of the old
Worthington shuttle valve duplex boiler feed pump. It has a pair of
cylinders with large pistons and narrow rods. A pair of shuttles control
the flow in and out of the cylinders. At top dead center the rods take up
about 15% of the volume of the cylinder.

Rather than discharging the high pressure brine through a pressure regulator
it is directed to the back side of a piston. The front side of the piston
pushes the new feed water into the membrane. Because of the volume that the
piston rod takes up the amount of feed water pushed into the membrane is
about 15% greater than the brine coming out. . That 15% has to go somewhere
and that is out the product side. After friction losses the Clark pump
can recover about 75% of the brine's energy so the net energy input per
gallon of product is less than half that of a traditional system.

The down side is that a Clark pump of acceptable size for a medium size
yacht can't pump very fast. (Under 1 GPM) They are pretty well limited to
around 6 or 7 gallons of product per hour which means you hear the whine of
the feed pump and click-clack of the Clark pump for hours on end.

--
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...
I still have more questions about RO systems. Manufactures quote their
system production rates in GPD and Amps. I compare them by calculating
product Gallons per Amp-hour, and the rates seem to be all over the board.
For example, Village Marine systems utilize about 2 AH per gallon for
their
Little Wonder Systems. HRO systems are 4+ AH per gallon.

The manufacture's publications make you believe that their systems have
become more efficient through their pump and motor technology. Is there
really that much difference in technology? Some vendors claim to have an
energy recovery system, but I don't understand what this is or how it
works. It certainly doesn't seem to apply to basic systems that I'm
looking at.

Any insights into this?

-- Geoff

Geoff Schultz wrote:

The manufacture's publications make you believe that their systems have
become more efficient through their pump and motor technology. Is there
really that much difference in technology? Some vendors claim to have an
energy recovery system, but I don't understand what this is or how it
works. It certainly doesn't seem to apply to basic systems that I'm
looking at.

Any insights into this?

-- Geoff

Spectra, Livol, and HRO Seafari "Escape" all use some form
of a similar looking pump that recovers some the energy in
the waste brine. Spectra uses one called the "Clark" pump -
a cutout drawing is on their website. In principle it's
simple; I'm sure the details of making it all work are a bit
more complex.

Spectra Ventura 150 gives 6.3 GPH @ 9 Amps. Catalina 300
produces 12.5 GPH @ 15 Amps.

The Livol D30C-12 produces 30 L/hr (7.9 GPH) @ 8.5 Amps.

The HRO 200 produces 8.3 GPH/13 Amps, clearly the worst
performer of this bunch.

Evan Gatehouse

Glenn,

Sorry to keep coming back to the same issues, but I just want to make
sure that I've really done my homework before talking to Village Marine
about my system. Since my system, and many non-state-of-the-art systems
don't have energy recovery systems, the formula for computing the HP for
the pump is:

HP = (PSI*GPM)/1460

Thus you have 2 or 3 things to play with on the right side of the
equation:

1) You can increase the PSI which will overdrive the membrane but will
increase production rates.

2) You can lower the GPM and drive the production rate on the membrane
above the 13-15% rate speced for the membrane which will cause the
membrane to foul more quickly.

3) One question I have is can you increase the efficiency of the pump
and thus increase the denominator? What is 1460? Is this some fixed
constant for all pumps or does this represent optimal case pumping?

On the left side you've got HP, and the only thing that you can do there
is to increase the efficiency of the motor. Are there really large
differences in the watts per HP based upon motor technology?

I have a reasonable understanding of RO system design in parallel vs
serial membranes. Parallel is out for me because it would require
doubling the feed flow rate for an additional membrane. Series is much
better as the flow rate to the following membrane only drops by the
amount of permeate (product) produced by the prior membrane and there is
also a corresponding pressure drop to the feed of the next membrane.
This causes the TDS (Total Disolved Solids) of the next membrane to
increase and this eventually limits the number of series membranes which
can be used.

So, what's 1460 and what differences are there in motor technology?

-- Geoff

1460 is called a "drive constant" for electrical horsepower. One HP is
33,000 ft. lb/minute and one cubic foot is 7.48 gallons. Consider a
cylinder with a cross sectional area of 144 sq in. (1 sq.ft.) place a
33,000 lb piston in it and pump one cubic foot of water into it in one
minute. The pressure is 33,000lb/144 sq in = 229.16 PSI * 7.48 GPM = 1714.
That is the hydraulic constant. Electric motor driven pumps range from 78
to 92% efficient with a mean of about 85% so 1714*.85= 1456. 1460 is
standard for all hydraulic pressure calculations with electric motors. With
a super premium 10 HP pump and motor at 90% you might use 1540 but no
practical electric motors under 2HP ever gets much better than about 85%.

1HP = 746 Watts. Mother nature does not allow us to screw around very much
with either.

--
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
...
Glenn,

Sorry to keep coming back to the same issues, but I just want to make
sure that I've really done my homework before talking to Village Marine
about my system. Since my system, and many non-state-of-the-art systems
don't have energy recovery systems, the formula for computing the HP for
the pump is:

HP = (PSI*GPM)/1460

Thus you have 2 or 3 things to play with on the right side of the
equation:

1) You can increase the PSI which will overdrive the membrane but will
increase production rates.

2) You can lower the GPM and drive the production rate on the membrane
above the 13-15% rate speced for the membrane which will cause the
membrane to foul more quickly.

3) One question I have is can you increase the efficiency of the pump
and thus increase the denominator? What is 1460? Is this some fixed
constant for all pumps or does this represent optimal case pumping?

On the left side you've got HP, and the only thing that you can do there
is to increase the efficiency of the motor. Are there really large
differences in the watts per HP based upon motor technology?

I have a reasonable understanding of RO system design in parallel vs
serial membranes. Parallel is out for me because it would require
doubling the feed flow rate for an additional membrane. Series is much
better as the flow rate to the following membrane only drops by the
amount of permeate (product) produced by the prior membrane and there is
also a corresponding pressure drop to the feed of the next membrane.
This causes the TDS (Total Disolved Solids) of the next membrane to
increase and this eventually limits the number of series membranes which
can be used.

So, what's 1460 and what differences are there in motor technology?

-- Geoff

"Glenn Ashmore" wrote in
news:XQeze.149130$sy6.77021@lakeread04:

1460 is called a "drive constant" for electrical horsepower. One HP
is 33,000 ft. lb/minute and one cubic foot is 7.48 gallons. Consider
a cylinder with a cross sectional area of 144 sq in. (1 sq.ft.) place
a 33,000 lb piston in it and pump one cubic foot of water into it in
one minute. The pressure is 33,000lb/144 sq in = 229.16 PSI * 7.48
GPM = 1714. That is the hydraulic constant. Electric motor driven
pumps range from 78 to 92% efficient with a mean of about 85% so
1714*.85= 1456. 1460 is standard for all hydraulic pressure
calculations with electric motors. With a super premium 10 HP pump and
motor at 90% you might use 1540 but no practical electric motors
under 2HP ever gets much better than about 85%.

1HP = 746 Watts. Mother nature does not allow us to screw around very
much with either.

Glenn,

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