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 capability. It is easier/cheaper to solve the waterproofing than make a self priming, continuously rated pump. It also deals with any cooling issues.
And stops freeze damage.
NT
They aren't
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 the user. 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
G.Harman
It's the type of the pump. If you remember your basic science. Lift and force varieties.
If you wanted one to to both, it would be a double pump so much more expensive. Same with car fuel supplies.
Cheap. All you need is a potted motor with an impeller in a case. They are extremely reliable with only one moving part.
The main reason is they're easy to install/remove/replace. Also cheap to make and ideal for the situation (pumping out of open water u nlike say central heating.)
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.
AJH
Maybe they'd survive on reduced voltage. If life weren't so short one could build something that would last a lifetime, perhaps using a bucket wheel.
NT
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 intermittent use!
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.
Less chance of freezing, too?
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 oversized solids... 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.
G.harman
Tell that to the folk that use industrial electrode heaters, kettles, washing machines, dishwashers, etc etc. It's just something we tell little children.
of course it does
NT
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 locality).
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 cooling setup.
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 subjected to.
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 combat.
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 evaporative losses.
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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