Throttle a pump harmful?

I've read here and on Marc's tank website that you shouldn't throttle
centrifugal pumps with a ball valve but that you should divert some of
the flow back to the intake side.

I hope I'm not being obtuse when I ask, "Why?"

Speaking specifically about Mag pumps, the manufacturer doesn't warn
about or otherwise recommend any minimum flow rates through the pump,
and the backpressure from a constriction in the line should be
identical to the backpressure from a higher head application.

At least that's what my math comes out to. I don't think the pump
can tell if the reason it's not pumping as much is because there's
a 5' head or an almost closed gate valve in the line.

If I'm wrong about this, could someone please take the time to
explain how the two cases (partially closed valve vs. increased
head) are different from the pump's perspective?

Or, alternatively, something else (not necessarily pump damage) may be
the reason to keep the flow through rate at a maximum. Perhaps
something like plankton mortality rates (just stabbing in the dark
here) that get much worse if the backpressure goes beyond a certain
point...

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

Ross, my whole reasoning is to avoid putting any undue stress on the pump, and
that is my only reason. Why add head pressure to a pump that doesn't need it?
I believe that the extra effort may lead to the pump running at a higher
temperature, possibly warming the tank water more.

Marc


Ross Bagley wrote:

I've read here and on Marc's tank website that you shouldn't throttle
centrifugal pumps with a ball valve but that you should divert some of
the flow back to the intake side.

I hope I'm not being obtuse when I ask, "Why?"

Speaking specifically about Mag pumps, the manufacturer doesn't warn
about or otherwise recommend any minimum flow rates through the pump,
and the backpressure from a constriction in the line should be
identical to the backpressure from a higher head application.

At least that's what my math comes out to. I don't think the pump
can tell if the reason it's not pumping as much is because there's
a 5' head or an almost closed gate valve in the line.

If I'm wrong about this, could someone please take the time to
explain how the two cases (partially closed valve vs. increased
head) are different from the pump's perspective?

Or, alternatively, something else (not necessarily pump damage) may be
the reason to keep the flow through rate at a maximum. Perhaps
something like plankton mortality rates (just stabbing in the dark
here) that get much worse if the backpressure goes beyond a certain
point...

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

--
Personal Page: http://www.sparklingfloorservice.com/oanda/index.html
Business Page: http://www.sparklingfloorservice.com
Marine Hobbyist: http://www.melevsreef.com

Ross / Marc

Do you have a pump curve? It's a long time since I was doing chem. eng. but
my memory says the pump curve gives flow / head / efficiency and power
consumption. Until you have a look at that you don't really know which
condition will generate more heat. I think stress on the pump should not be
an issue -- they should be designed to run within their stated range.

Phil


"Marc Levenson" wrote in message
...
Ross, my whole reasoning is to avoid putting any undue stress on the pump,
and
that is my only reason. Why add head pressure to a pump that doesn't need
it?
I believe that the extra effort may lead to the pump running at a higher
temperature, possibly warming the tank water more.

Marc


Ross Bagley wrote:

I've read here and on Marc's tank website that you shouldn't throttle
centrifugal pumps with a ball valve but that you should divert some of
the flow back to the intake side.

I hope I'm not being obtuse when I ask, "Why?"

Speaking specifically about Mag pumps, the manufacturer doesn't warn
about or otherwise recommend any minimum flow rates through the pump,
and the backpressure from a constriction in the line should be
identical to the backpressure from a higher head application.

At least that's what my math comes out to. I don't think the pump
can tell if the reason it's not pumping as much is because there's
a 5' head or an almost closed gate valve in the line.

If I'm wrong about this, could someone please take the time to
explain how the two cases (partially closed valve vs. increased
head) are different from the pump's perspective?

Or, alternatively, something else (not necessarily pump damage) may be
the reason to keep the flow through rate at a maximum. Perhaps
something like plankton mortality rates (just stabbing in the dark
here) that get much worse if the backpressure goes beyond a certain
point...

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

--
Personal Page: http://www.sparklingfloorservice.com/oanda/index.html
Business Page: http://www.sparklingfloorservice.com
Marine Hobbyist: http://www.melevsreef.com

Hi Ross

For most impeller pumps and centrifugal pumps it wouldn't matter at
all, because they are designed to operate within a wide range.

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.

We have similar set-ups on all of our bottle filling equipment, except
instead of a manual valve it has a spring loaded ball valve that can
be set at various pressures. When the filling head solenoid opens,
you have the desired head pressure. When the filling head valve
closes, the spring loaded valve is forced open with the excess head
pressure and allows the product to recycle back to its own carboy
(sump). Some systems use a split solenoid so that when one side is
open the other side is closed, but you get unequal head pressure for a
split second as the solenoid switches, which can cause a splash of the
product, so these split solenoids are rarely used. In fact, most
small bottlers and repackagers use gravity feed rather than pump feed
to save costs on electric and equipment replacement costs.

TTUL
Gary

am (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

Ross

You need the pump curve for the particular pump to answer those questions.

Phil


"Ross Bagley" wrote in message
...
am (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

"Phil Krasnostein" writes:

Ross

You need the pump curve for the particular pump to answer those questions.

Given these pump curves, what can you tell me? Or is there another curve
(more/different data) that would be needed to answer my question?

http://www.marinedepot.com/aquarium_...on.asp#qone800

There's definitely a "belly" to the curves and it seems that if you
chose a point where the area within the rectangle of the flow and
height is maximized, you may have found some sort of a sweet spot.

But is that sweet spot likely to have the lowest wear on the pump? Is
the pump likely to run most efficiently and produce the least waste
heat at that point on the curve? What might that sweet spot mean
to us as aquarists?

Thanks for all the help,
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

Given these pump curves, what can you tell me?

for what you are after, no one can tell you anything from those graphs

Or is there another curve
(more/different data) that would be needed to answer my question?

very much so, you need one that has that curve and some kind of electrical consumption
curve(you could get the answer from almost any electrical curve), it would be nice to have
a MTBF curve added to that, another might be heat transfer.

when water moves slower thru a hot object it picks up more heat some of that is set, some
of it depends on what the water is moving thru.



There's definitely a "belly" to the curves and it seems that if you
chose a point where the area within the rectangle of the flow and
height is maximized, you may have found some sort of a sweet spot.

But is that sweet spot likely to have the lowest wear on the pump? Is
the pump likely to run most efficiently and produce the least waste
heat at that point on the curve? What might that sweet spot mean
to us as aquarists?

that sweet spot probibly doesnt mean anything, except where the most gph is. most
aquarium pumps dont list the data you want. some larger like 1/4+ hp pumps do.


--
Richard Reynolds

Ross
These curves are simple and don't tell you much. You also need efficiency
and power consumption data. For some general info, have a look at

http://www.mcnallyinstitute.com/06-html/6-01.html

In my experience, centrifugal pumps are generally designed to be throttled
by valves, and won't wear out because of it -- certainly energy loss across
the valve restriction will generate some heat.

Phil

"Ross Bagley" wrote in message
...
"Phil Krasnostein" writes:

Ross

You need the pump curve for the particular pump to answer those
questions.

Given these pump curves, what can you tell me? Or is there another curve
(more/different data) that would be needed to answer my question?


http://www.marinedepot.com/aquarium_...nbow_lifegard_
quiet_one_information.asp#qone800

There's definitely a "belly" to the curves and it seems that if you
chose a point where the area within the rectangle of the flow and
height is maximized, you may have found some sort of a sweet spot.

But is that sweet spot likely to have the lowest wear on the pump? Is
the pump likely to run most efficiently and produce the least waste
heat at that point on the curve? What might that sweet spot mean
to us as aquarists?

Thanks for all the help,
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

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