a question regarding pumps i couldn't answer

[dick benbow]

One of the things I enjoy is sharing the knowledge I know, when i don't have an answer, I like to get one.....your knowledge requested....regarding pumps

centrifical pumps outside a body of water as opposed to a magnetic inside or submerged in the same water as the koi. What concerns should one have as to an effect the koi may experience with the use of the submersed pump? This pump would be protected with GFI...we're focused only on anything magnetic or electrical that may have adverse affects....

[Russell Peters]

Quote: Originally Posted by dick benbow One of the things I enjoy is sharing the knowledge I know, when i don't have an answer, I like to get one.....your knowledge requested....regarding pumps centrifical pumps outside a body of water as opposed to a magnetic inside or submerged in the same water as the koi. What concerns should one have as to an effect the koi may experience with the use of the submersed pump? This pump would be protected with GFI...we're focused only on anything magnetic or electrical that may have adverse affects....

The only problems I have ever run into, with a magnetic or submersable pump, are a short that can cause electrocution or an oil filled body that leaks. If you protect the pump with a GFCI and it is not oil filled, it is my opinion that you would have no problems.

[jnorth]

Other then an oil filled pump leaking the only other thing I've heard of is of course electrocution from a short. So the cure for that is GFIC. Of course GFI isn't fool proof. If you don't test them every now then you may not know it is broken and then the pump might fail and the koi get shocked. Sometimes when I shut down my pumps for filter cleaning I like to do it by hitting the test button on the outlet to make sure it's still working. I think if I had a submersible pump I would do it that way quite regularly.

[mitten]

I think there is another part to the effect that a submersible pump could have. As part of filter cleaning it would be shut off and then turned back on. This would be done infrequently in a well designed filter system with passive settlement that oould be dumped by valve turning daily, that's true, but this type of pump would be more likely to be associated with a system that contained a "pond" filter from some manufacturer who considers that degree of solids filtration for nuts only.

When a motor starts up there is a field of energy created around it and fish near enough to it and small enough or weak enough would be affected by this charge. This is not a malfunction of a pump, has nothing to do with GFI, and is more pronounced in larger pumps.

These are all beliefs that I have based on reading. I am not an engineer, though Daddy was, and can't back this up with quotes or sites, or cites, or links. An engineer may wish to back me and my memories up or may well blast me. My only anecdotal experience was one otherwise unexplainable curved back in one of my first tanks, equipped with a mag 12.

I like the idea. I like the simplicity of plumbing setup. I don't use submersible pumps in any tank with fish. The last chamber of a multi chamber filter is a good place to put it if that's the way you're going to go.

Mickey the windowman

[dizzyfish]

There is also the issue of voltage leaks with submersible pumps. While this is generally not a serious problem for larger koi, fry can possibly be adversly affected. It has been suggested that crooked tails on fry can result from this. It is easy enough to check for voltage in the water using a voltage meter on the low AC scale. Stick one probe to ground and the other in the water and see if you get a reading. I found two fry tanks that had readings of nearly 9 volts this year and some of the fry in both tanks were experiencing crooked tails. It was not enough that you could feel a shock. Gounding the water appeared to stop the problem.
Mitch

[Akinosan]

My first pond was built with a submersible pump from Aquascape and was on a GFI circuit. The pump shorted out killing seven fish and putting a kink in the spine of 4 others. I'll never use a submersible pump again.

[frankchong]

I have been using submersible pumps for my 45 tons pond as the main filtration pump since 1999. I have not had an incident where my koi is electrocuted. The pump will fail after one to three years of operation depending on the manufacturer, some last longer than others. The nature of failure I encountered are 1) Open circuit in magnetic coil. The pump just stop running, electric circuit intact, no tripping. 2) Pump seal leakage, water ingress into magnetic coil cause current leakage. In this situation the Earth Leakage Circuit Breaker in my main distribution board would trip until the pump is switched off.

All submersible pumps that I have used are filled with turbine oil and I have never encountered any oil leakage in the event of pump failure. I could be lucky though.

My pump is located inside filtration chamber. But I have seen many ponds converted from water garden pond where there is no bottom drains. The submersible pump would be sunk inside the pond itself. From my observation the koi do swim around the sub pump and not avoiding it. Therefore I conclude that the koi do not seemed to be adversely affected by the sub pump.

[bekko]

Submersibles always self-prime and are easy to install.

But, think about all the extra considerations and design elements that go into manufacturing a submersible compared to a traditional non-submerged centrifugal. In exchange for being able to run under water, you must either pay a higher initial cost or suffer a shorter life expectancy. There is no free lunch. I have never seen a submersible which was as electrically efficient as a good centrifugal either.

Magnetic drive submersibles do not need a shaft seal (where the shaft penetrates the pump head). Thus, the motor can be completely encased in some sort of coating which makes them less likely to leak oil. Shaft seals are often the weakest link. However, magnetic drive pumps are usually more expensive to buy and less efficient in terms of their electrical use. For non-submerged applications, a magnetic drive usually only makes sense when pumping saltwater or other corrosives. Saltwater can pit a metal shaft and cause the seal to fail prematurely.

I often put my life in the hands of GFIs. So far, when they have failed they fail by tripping out prematurely (with little or no imbalance or short-circuiting). When one fails to trip off when it should I will not be able to report back here. Nonetheless, a GFI will tolerate a certain small degree of imbalance before it trips. I cannot quantify the watts, but it is enough to feel as a tingle. Whether that small amount of imbalance is enough to harm fish of any size, I do not know.

I had never even thought about the impact of the rotating magnet on fish in the surrounding water. That's interesting. However, I have thought a lot about underwater noise and seen pretty clear adverse effects - but not with koi. Submersibles inherently generate more underwater noise but a non-submerged pump will also create underwater noise via the suction pipe. In some applications, you need a flexible section in the suction line to dampen noise.

-ste veho

[frankchong]

Quote: Originally Posted by bekko Submersibles always self-prime and are easy to install. There is no free lunch. I have never seen a submersible which was as electrically efficient as a good centrifugal either. -ste veho

This statement may or may not be true depending on your operating point. By operating point I mean the Q ( flow rate ) and total static head and pipe losses. In centrifugal pump selection we started of by deciding what flow rate we want. From the static head and pipe loss head calculated we know the total head. With the known flow rate and total head we can determine what is the power required to drive the pump from the pump operating curves. If the pump at this operating point needs a 1/2 horse power motor well and good you have a maximum efficiency pump. However if the operating point requires a motor say slightly bigger than 1/2 hp. One would have to select a 3/4 horse power motor, in this situation the electrical efficiency would be lower.

For submersible pump the manufacturer is able to tailor made the motor size to suit the pump power requirement to limit wastage. As far as electrical efficiency is concerned the trick is to select a pump operates at optimum efficiency at a given flow rate and head. Centrifugal pump may or may not be more efficient than submersible pump, but one thing is certain, non submersible centrifugal is more reliable and certainly last longer.

[bekko]

I never heard of a submersible with a taylor made motor size, but will take your word for it. Although, if you can get a taylor made motor for a submersible, then you should be able to get one for a traditional centrifugal as well. No?

I buy pumps off-the-shelf and don't get the impeller shaved in order to hit the sweet spot, much less have a custom made motor. In looking through the catalogs the submersibles always have a higher amp draw than a centrifugal with the same capacity. If you have any recommendations, I'm in need of a submersible which will deliver 60 gpm at 5 feet TDH for less than 220 watts and less than $400.

-steveh opk