jillybee23

Submergeible vs. External Pumps

11 posts in this topic

Hello All:

I will be setting up a 150 gallon 3 bed system. I would prever to use a submergible pump but my husband would prefer to use an external marine pum. What pump would be best suitable.

Also, what size of pump would you recommend?

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sub pumps are usually more efficient less wattage also they are obviously cooled by the water so no overheating problems as for size work on at least a complete water change every 4 hours so if pump only runs 15 min per hour get a 600gph pump if it runs cont then 150 gph there are lots of variables stocking densities ,temp,gb to tank ratios,type of system raft,cont flow ,flod and drain so this is just a rough guide

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Hi,

Here's my take on pumps:

  • Submersibles are more convenient (no wiring and minimal plumbing).......and that's the principal reason that people use them.
  • Submersibles actually cost more to run than an external centrifugal pump of the same pumping capacity.
  • Submersible pumps are actually quite inefficient when it comes to moving water - generally because of poor impeller design. Centrifugal pumps are often not much better. If you want to move water at minimal cost, you would probably go for an axial flow pump (Frank, where are you when I need you?). Suffice to say, small AP systems overwhelmingly use submersibles for reasons of convenience and cost.
  • Submersibles usually work out cheaper than a centrifugal pump of the same capacity......depending on what brand you buy.
  • Centrifugal pumps will usually pump to a greater height.
  • Buy more pump of greater capacity than you actually need in case you under-estimate the amount of water you need.....or you decided to add more growing systems.
  • You have a choice of cheap Chinese pumps......or something like Laguna range which will cost up to five times as much for the same capacity but will have a three year warranty.
  • Regardless of your pump choice, if it stops (and you don't discover it relatively quickly) you'll have dead fish on your hands so factor a back up system into your AP system design.
  • Don't mess with 12 volt marine pumps.....they cost the earth and they generally don't last too long. These are generally only used as back up system pumps where they are not expected to be running for days on end.
  • Design your system up so that your pump runs continuously - starting and stopping small pumps shortens their operating life considerably.

Good luck and welcome to APHQ.

Gary

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Gary my 85 watt pond pump pumps 6000lph at 1000mm head i haven't found any externals that efficient if you know of any at $120.00 or less please let me know regards Bart

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Hi Bart,

I've acknowledged that submersibles are the pump of choice for many AP systems on the basis of cost.

Cost (and pumping rate for that matter) are not the only measures of efficiency. I believe that non-submersible centrifugal pumps will pump more water for the same power consumption.....and they'll pump it higher, too.

Having said that, they can be hard to find.......particularly in the 2,000 - 10,000 litres per hour range.

Even among submersibles, pumps can vary quite considerably in terms of pumping capacity, head and cost.

Gary

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I run an in line pump 28.000 litre a minute for 3 min every hour costs about $45.00 a year on power its been running on my ap for 3 years and before that it ran a swimming pool for 10 plus years

with the pressure it gives i have a bleed back to the sump [bottom always clean ]

I run 25 mm then 20 mm pipe from the pump and never had a biofilm blockage

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A submersible pump is still a centrifugal pump, Gary. They operate almost identically to an external pump.The only real difference is extra drag on the rotor (since its in water instead of air) which is countered by the fact that external pumps need cooling fans. Now you could say most external pumps are more efficient than most submersibles and you'd be right. That's because external pumps are typically big pumps where as many submersibles are small pumps.

Size is what makes by far the biggest difference, bigger pumps can be more efficient because they have a smaller surface area to volume ratio. Hence less friction losses per litre pumped. When I bought my pump (45w, 2500lph submersible) I remember comparing it to a 1kw external centrifugal pump when I bought it and it was almost identical in efficiency. I can well believe Bart's pump (twice as big as my pump (yes, I'm jealous), and what do you know, more efficient) has actually surpassed a typical external pump.

The way you guys run your systems, the centrifugal is the most efficient pump. It's in its element with high volume, moderate pressure. Now it true that an axial flow pump will move more water per kw, but only with very low heads. So you've got a few technical problems to solve before you start using one of those.

btw Gary when you look at a typical small pump submersible and think that impeller is poor design its not really true, its just that the benefits of contouring, and staging, and streamlining, you see in big pumps just don't exist on those small scales.

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Hi,

A submersible pump is still a centrifugal pump, Gary.

I understood that.......I was looking to differentiate submersibles from the non-submersibles........and there was probably a better term than external.......but it eluded me. In any case, once you get them outside of the tank, there are so many different types that specifying centrifugal is probably still a useful distinction.

Gary

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ok...forgive the newbie here

I found the pump below on Harbor Freight Tools website. I'm trying to figure our if such a cheap submersible pond pump ($24.99) with the specs below would move a sufficient amount of water for a flood and drain system with a 150 gallon fish tank and 36-50 sq ft grow bed .

High quality pump adds life and beauty to your pond. Shoot a fountain of water skyward or create the look of a natural spring with the included adapters. Ceramic shaft permits use in both fresh and salt water. Reliable and quiet, this pump is also great for use in large aquariums.

Includes two adapters—sprinkler head and waterfall head

Inline flow control valve

Removable filter for easy cleaning

Removable stand with suction cup feet

Gallons per hour: 258; Lift: 6.4 ft; Motor: 110V, 20 watts; Power cord length: 19 ft. 5"; Overall dimensions: 8" W x 6" L x 3-1/2" H

Weight: 2.8 lbs.

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I'm setting up my first AP garden. I'm wanting to set up a sequencing (indexing) valve with an external water pump to feed my grow beds   However, my concern is having to turn the pump on and off to activate the valve and causing early demise of the pump.  Would a submersed pump have less stress?  Any suggestions would be greatly appreciated.

Flo

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Hi JustFlo

Welcome to APN/HQ

I prefer a dry mounted  (external) pump, no more stress on that.(also safer with no wiring in the water)

Unfiltered water on the other hand will have some more stress on any pump impeller, so mounting pump after filters is a positive design.

cheers

Edited by ande (see edit history)
bigdaddy likes this

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