Hi Ross

It's very simple to hook up an ammeter to check the current draw as
well as a thermometer to check motor temperature.

It only makes sense, that to do MORE work, will require MORE energy
and produce MORE heat.

We use MaxiJet1000's to pump heavy viscous liquid, they are the
coolest running of all submersibles we have tried, but do run right at
their automatic shut-off pre-set temperature when the backpressure is
idling high for a long period of time.
The benefit to using MaxiJet's is that they DO HAVE internal thermal
sensors to shut them down, rather than burn them up as some pumps we
have tried.

Higher heat, higher resistance, higher electrical consumption!

You are correct about SOME pumps that REQUIRE Head Pressure to run
more efficiently because of their design.
Although not seen much in aquaria usage, worm drive and screw drive
pumps often need a 'load' on them to function efficiently. Some worm
drive pumps without a 'load' will self-destruct from backlashing of
the gears.

Magnetic driven pumps one would think would not be affected at all by
head pressure, because there is no interaction between the impeller
and the engine, which is just an electromagnet being pulsed to drive
the core which spins the impeller.

But under a heavy load, the core heats up, which in turn causes the
winding driving it to heat up and under enough load, it will get hot
enough to trip the thermal sensor (if your pump has one).

If the load (backpressure) is too great, the magnetics breaks down and
the engine cannot overcome the load on the core.
Most magnetic driven pumps have floating impellers, you will often
hear them chatter as you start up the pump. This is to prevent the
magnetics breakdown as the pump starts and keep start up heat to a
minimum. If you rigidly affix the impeller to the core, you will find
that most magnetic pumps will keep losing their magnetics hold on the
core as they try to start and in some cases may not start at all.

In essence, an alternator works the same way, load it down and it will
heat up.

TTUL
Gary


(Ross Bagley) verbositized:

(Gary V. Deutschmann, Sr.) writes:

[...snip...]

But there is a better way than clamping down the output feed line.
Install a T-Fitting in the output line and a line connected to the
T-Fitting as a return line to your sump, you can install a valve or
clamp this line to increase output from the feed line.
This method works well on all pumps, keeps heat buildup lower and
places less stress on the pump.

Thanks for the answer. This does respond to the core of the
question that I was asking. So what you're saying is that operating a
pump at a higher head does a few things:

1) increases wear/stress on the impeller/motor
2) increases heat production/reduces efficiency

Both sound reasonable and plausible, but I have heard that lower flow
rates can make some pumps work less (that they can work more
efficiently at heads greater than 0ft than they do at 0ft). This has
been asserted for the Rainbow Lifegard Quiet One pump on this very
newsgroup. This assertion is also plausible if the efficiency of
a pump is nonlinear (goes up at lower pressures, then drops again
at higher pressures, going back to zero at the pump's max head).

Now, what I really wonder is: does anyone have any actual numbers to
support either set of assertions. These numbers might only apply to a
particular make/model of pump, but any empirically gathered numbers
would help to satisfy my curiousity.

Regards,
Ross

-- Ross Bagley http://rossbagley.com/rba
"Security is mostly a superstition. It does not exist in nature...
Life is either a daring adventure or nothing." -- Helen Keller