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