Why is it that pond pumps are always submersible ones?
I can see no good reason why the pump can't be external to the pond as
long as it's self-priming (only to a small extent). Much easier to
make and to maintain then.
But they are simple impeller pumps and have almost zero self priming
It is easier/cheaper to solve the waterproofing than make a self
priming, continuously rated pump. It also deals with any cooling issues.
Yet the ones I use with float switch and thermal overload cut outs do
seem to fail, just over a year pumping out a cistern which fills if a
soakaway cannot cope. I've tried several brands and they all seem to
fail with the stator shorting to earth.
This even though they are continuously rated in the spec sheet.
I suspect *submersible* does not imply permanent immersion. I have a
cheap Italian made pump which I use to top up the garden pond from a
shallow well. Used a few times a year, this has now done about 15
seasons. It spends most of its time on a shelf in a shed.
The impeller seals may not withstand the pressure changes due to
seasonal thermal cycling.
Mind, there is also the very cheap (?25.00) pump which powers the
*gurgle* in our back yard. Five years of permanent immersion and very
though once you get to that size then they are not exclusively pond
Different markets, most of what are called pond pumps are smallish
things that can be safely dunked into pond and using a longish cable
connected safely to a supply without too much technical knowledge from
If it just for a fountain then often no extra plumbing is needed at
all. Maintenance will involve pulling it out occasionally and washing
down/back flush with a hose. The motor and its connections will be
manufactured easily by sealing them in at manufacture and if a
magnetic coupling is used as many do then that is it ,no servicing
possible but will last for years if it is a good make.
It will be bearings that wear anyway and very few people would bother
to replace those themselves.
Start going to chambers by the side ,plumbing to disconnect and seals
to maintain then I reckon you are leaving the world of simple Pond
Pumps and moving into the world of pumps generally which might appeal
to those with an engineering bent or background but beyond the
capabilities of many people who just want to buy something and use it.
I have a bit of both, Oase 12 DC pond pump which is still running a
few years over its 5 year guarantee,
For fun occasionally I run an old Lister domestic H1 similar to this
just because it is nice to see something mechanical working .
Mine isn't quite as immaculate but works fine.
They arent always, but submersibles are easier to use much of the time.
Not really. Doesn’t make a lot of difference to the making
and its easier to make a submersible self priming.
Easier to maintain in some ways when you can just take
it out of the pond when you need to do anything to it.
None of the explanations here cite the reason as pumping capabilities of
a centrifugal pump on different densities of fluid.
Simply the pressure at the edge of a vane is a function of rotations
speed, diameter of impeller and directly proportional to density.
Since the density of air is 1/800 of water the pressure of pumped
air/vacuum would not be able to overcome any height of water.
Submersible - Easier to hide, less chance of it running dry if a pipe
splits, one less joint to leak, significantly quieter, fixes the water
draw-off point in the right place at the bottom of the pond rather than
a free-swimming pipe, easy to cage the pump to prevent ingress of
I'm sure there are other reasons too like not such an issue if the
casing halves leak.
Easier to maintain as the inlet is the side that will block from weed
etc so no pipes to disconnect and you can see if it's blocked or not
just be lifting it from the water...
Most of the smaller pond pumps have a motor totaly encapsulated in
plastic at time of manufacture. The connection to drive the impellor
is a magnetic coupling. There is no shaft or gland to wear out and
start leaking which is the weakness of any pump witha mecahnical shaft
from motor/engine to pump impellor.
On Fri, 05 Aug 2016 18:46:07 +0100, damduck-egg wrote:
A fact that's taken advantage of by those cheap, no name, water cooled
'sealed for life' CPU heatsink kits used by some PC systems builders
where the CPU water block incorporates the circulator pump based on the
same magnetically coupled impeller design.
I know about these rather pretentious CPU 'cooling solutions' from a
recent experience with my daughter’s 'custom built' PC which she had lent
out to my son after it had been in storage for some 6 months or more in
our front parlour (the result of a house move and our willingness to save
her and the SiL the costs of storage whilst they were living in a rented
rabbit hutch when house hunting for a more permanent residence in the
After said son had spent a day setting this "Turbo-charged" desktop
tower PC up and downloading the latest updates for the latest of one of
the many first person shoot 'em up games (a Command and Conquer-a-like -
possibly even *that* very game) he started seeing the game slow down and
stutter within a matter of minutes of starting to play the game,
discovering that the cpu was throttling back due to excess temperature
(86 deg C Istr) which lead to my involvement in diagnosing the cpu
Initial examination showed a spot of corrosion lifting the copper
plating off the cheap die cast or aluminium water block come circulator
pump which I thought may have been lifting the block away from full
contact with the cpu heat spreader. There was also some discolouration
suggesting a slow leakage of coolant, presumed to have been slow enough
to have evaporated away harmlessly.
undiscouraged by this, I dressed the spot of corrosion down with a fine
file and we reassembled it to test my remedial work. Needless to say, if
anything, it seemed slightly worse and I eventually realised that either
the pump impeller wasn't actually spinning or else the coolant had leaked
out. It turned out to be the latter, at which point we both decided
against wasting any more time trying to effect a bodge repair by trying
to recharge it with water when the initial leak may well have been
aggravated by the extremely high temperatures it had recently been
I opined to my son that a good quality traditionalfan cooled heatsink
would do an equally (if not more) effective job than that cheap no name
water cooling kit had managed at its peak of performance.
I don't think my son decided on this course of action until he realised
that he'd be spending silly money on fitting another expensive water
cooling kit on a computer that he was only borrowing and did not own.
A few days later, we took delivery of the fan cooled heatsink my son had
ordered from an Ebay trader and I was (once more) roped into fitting the
replacement heatsink assembly and, for a few hours afterwards, I was
treated to the thumps of explosions and various sounds of house to house
Taking time out to pop upstairs to his bedroom, I was able to witness a
very smooth high framerate rendition of the game in progress which was
all the proof I needed to confirm my opinion regarding a fan cooled
heatsink as being a more than sufficient alternative to the originally
fitted water cooling kit. :-)
I think the problem with this cheap water cooling option was the use of
crap materials and the combining of the pump impeller into the water
block itself in a "Sealed for Life", non-refillable cooling system
intended to be fitted by unskilled labour.
Quality water cooling systems (which require a higher level of
mechanical and plumbing skills than the average home computer enthusiast
would typically possess) use a seperate pump and simple water blocks
fabricated out of solid copper, generally coupled together with
transparent tubing which allows inspection for signs of low coolant level
or pumping problems.
However, as I recall, these are normally filled via the heat exchanger's
header tank which allows visual inspection of fluid level and, I'd
expect, obvious signs of coolant flow - the temperatures normally remain
well below boiling point and don't require to be sealed against pressure
build up as in the case of a car radiator - just sealed simply to reduce
The point to note with all of these liquid cooling systems, regardless
of quality and expense, is that magnetically coupled impeller designs are
used universally simply to eliminate reliance on shaft seals which will
eventually start leaking sooner or later - there'll be problems enough
with coolant leakage just with the static seals on pipework couplings
alone (but problems here are more readily dealt with and amenable to home
repair than in the case of a leaking shaft seal on a miniature 12 volt
brushless DC motor driven pump).
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