"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