Jed Rothwell wrote:
Stephen A. Lawrence wrote:
The pump is specified by its manufacturer to require drive from a 10
HP engine in order to achieve its rated performance.
Actually, if the manufacture's specifications call for a 10 hp engine,
that means anything bigger will wreck the pump. They usually specify the
highest power level that can be used with a pump. In actual use most of
the time it is a fraction of 10 HP.
So I was being too generous to them :-)
Look at it differently.
The motor requires 20 watts of input electrical power.
I hesitate to give credence to Neuman et al., but if the pump moves at
all with only 20 W input, that is remarkable. 10 hp = 7,457 W. Even at
low power, 1/10th the top rated power, it would consume 700 W. Pumps,
automobile engines and other heavy equipment of this nature has
considerable friction. You cannot usually turn these machines by hand,
and you can easily apply 20 W with your hand. (By comparison, peddling a
bicycle hard with your legs generates ~200 W.) It is hard to imagine a
pump of this size producing any flow with only 20 W.
That thought crossed my mind too. But ... as far as I know they haven't
said what brand and model the pump is. We can be reasonably certain
this pump was not chosen at random.
I can't say how they selected the pump, but if I were doing this I would
look for a pump with a high rating, but which had low internal friction,
such that it would operate (at a low rate) with small torque.
It's a "positive displacement" pump, which, I would guess, means it's
reciprocating (or wabble-plate) rather than rotary. One consequence of
that is that if you can get it to turn at all, no matter how slowly, it
will pump (some) water.
A rotary pump using a turbine, on the other hand, would require some
minimum spin rate in order to do anything at all.
A rotary pump with flexible impeller, like the old Jabsco pumps I recall
from the days of my youth, takes a fairly significant and irreducible
torque just turn at all, as the impeller blades need to be "squished" as
it goes around.
But a reciprocating pump should, I would think, present no resistance to
turning other than friction in the bearings and rings.
By the way, have they said anywhere that the pump is a straight-up
unmodified off-the-shelf unit? I don't recall seeing such an assertion.
*********************************
Remember Klipschorn speakers?
Sometimes high power handling capacity and high efficiency come together
in one package.
So there is a mystery here. But it will only be explicable if they give
us some real information.
- Jed
