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

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