|
Excellent chart Bill, it shows it all. I'm
sure you are right about the EWP HP saved claim although I think the success of
the EWP is due to several factors. Just a SWAG but I think they
are:
1. As you said, The EWP never runs at the
high end of the rpm spectrum where the stock pump is absorbing excessive HP
(and perhaps a *little* more flow).
2. The cooling requirements of the engine do
not need the upper limit of flow that a mechanical WP could
provide.
3. The efficiency of the EWP is probably much
better than the engine driven pump so it doesn't need as much power for a give
flow rate & head. Haven't seen the DC pump innards but the
Mezzier EWP is a surgeon's tool if the stock WP is an axe.
The EWP pessimists always point to "More flow is
better" which is correct to a point, but ignores the real world requirements of
what it takes to do the job. Another case of perfect being the enemy of
good maybe.
Tracy Crook
Here is a .GIF that illustrates both our points.
At zero flow, the pump shaft horsepower is less than at rated flow, but all
the energy is going into heating the water.
I believe that the reason Davies Craig claims
that they save a lot of horsepower, is because at high rpm, the pump is not
running at its high efficiency point. It is clear from the successful EWP
tests of Todd, that the actual energy required to pump the water is small. So
if DC is correct, then they are using the high rpm point for the "horsepower
saved".
Bill Schertz
|