questions from millie

[millie]

hi, if the fish tank is 1 000 liters big wat size pump do u use....like how much water is needed to be pumped out each hour or do u werk in days.......is ther a low figger when getting a pump ?

[talking2u]

Hi, millie.

with aquariums I know you want to cycle your water (pump your water) every hour. that is if you have a 50 gallon tank you would cycle your water 50 gallon an hour.

I have a fish pond 450 gallons and my pump cycles 475 gallons an hour. The question might be can you cycle less water, and still give your fish the adiquite oxgen they need? With Murray method of cycling on for 20 minutes off for 45 then what? I guess that is why they have extra bubblers.

I will pass this little tidbit I learned the hard way. my tank is approx 10 x 3; I was pumping my water out form one end and replacing it back via a water fall from the same area. My tank amonia was to high and the ph was off....I was told it was becasue my pond was stagnant at one end. I could not figure out why I had a strong enough pump. They suggested that I change my pump take in to the other end of the pond. ALLproblems were solved! Hopes this helps. Have a great day. Talking2u-Jan

[millie]

tnks for thet, isnt Murray using a 15 000lph pump and doing 3 mins on an 45 mins off ?

This is wot wos confusing, thet big a pump for thet short of time is liek puttin a V8 in a volkswagen and only hitting the gas wen going up hill an then say tis econmical, 20 mins on is much better....tks for clearin thet up

[Murray]

Millie,
There is no right or wrong really.
If you are doing flood and drain then the idea is to fill the bed, than let it all drain out back to the fish tank.
There are a few different ways that can be done, all of them just as successful.
In my case the pump moves about 150 ltrs of water per bed into the bed in 3 or 4 minutes, then switches off to let it all drain back. You could use a smaller pump and pump the same beds full over, say 10 minutes, then let them drain back to the fish tank.
My tank has 2000 ltrs capacity so I am moving approx 600 ltrs of water around every 45 minutes. It would therefore take 3 and a bit pump outs to completely move all the water in the tank once.

[njh]

It's hard to say which pump schedule is most efficient as there are a number of competing effects:

motor efficiency: bigger motors are generally more efficient

impellor efficiency: bigger impellors are more efficient due to smaller boundary layer

inertia: a certain amount of energy is not recoverable when starting the water moving - the larger the pump and the longer the pipe the greater. A similar effect applies to the motor and the power supply.

pipe friction: larger pipes have lower friction

turbulence: small pipes joining to large pipes can form turbulence back pressure reducing efficiency

motor heating: a motor become less efficient when run for longer as the windings heat up and become more resistive.

So really, you can't say whether bigger or small is better. You can only consider two complete systems in comparison.

I would expect a pump that is on for 15 minutes in the hour is probably a reasonable compromise.

One thing that is always an advantage is to tune the pump size so that the water comes out of the pipes into the grow beds with no residual energy - you want the water to come out as if it were just trickling out of a bucket.

(And I'll say it again, because people continue to ignore me: centrifugal pumps are not a good choice for the large volume, low head flows used in AP. Design an axial flow pump and you'll probably cut your power consumption to a tenth.)

[GaryD]

Hello njh,



(And I'll say it again, because people continue to ignore me: centrifugal pumps are not a good choice for the large volume, low head flows used in AP. Design an axial flow pump and you'll probably cut your power consumption to a tenth.)


For many of us, it's probably less a matter of ignoring you than one of not understanding fully what you're talking about.

Small submersible centrifugal pumps get used because they are cheap, convenient and readily available......axial flow pumps less so.

When your pump is costing just cents per day to run, power saving (for most of us) becomes academic.

Gary

[Murray]

NJH,
I would really like to try such a pump, (axial flow) but I am not able to see any avbl
I know from personal experience that axial flow or "screw" compressors are much more efficient, but they are only found in much larger machines. Perhaps it is the same with water pumps.

Here is a link to a cutaway drawing of an axial flow pump.
http://www.flowserve.com/vgnfiles/Files/Images/Products/Pumps/ps-40-3_main.jpg

[millie]

tks ppl for clearin thet up, will sit down with paper an do drawing of wot i hope to do:)

[fishfood]

Murry axel flow pumps try a pump out if a swampy air cooler they are axel flow you know the ones on the roof [ a friend extended the sharft 2 ft for his lathe coolant]

[njh]

Yep, that's the sort of thing, Murray! I'm suggesting attempting to fabricate one using blades from a computer fan and some pvc pipe. I'm sure that people as crfafty as you and fishfood could work out a simple design using readily available parts. My swamp cooler does indeed have an axial pump, but I'm not willing to dismantle it just yet :)

Yes, using a pond pump uses only cents of electricity, but why stop just because our economic system undervalues energy? The same argument works against AP in general - why grow fish when you can buy them for less than the capital cost of the system. If you can drop your energy consumption enough, self powering systems using PV become practical.

[Murray]

NJH, I was taking a further look at the principals behind the axial flow pump, kept following links, and came across this on Wikipedia
http://en.wikipedia.org/wiki/Archimedes_screw

Very interesting.
Just shows that there are not many new ideas these days.
Muzza

[nogreenthumb]

Cool link muzz......how did you find this one?

[njh]

Give it a shot and see how well it works. You might be able to use a ground screw (used for holding down ropes) for your spiral. The fact that the casing can be joined to the screw suggests that you could make a very simple mechanism to drive it.

The idea of using it to lift fish is intriguing.

[Murray]

Nogreenthumb,
There is this amazing thing ..........Google.
and............... Wikipedia.
As you can see in this thread earlier we have been talking about axial flow pumps.....Google that and start following some links and it is not long before you come across the Archimedes screw, the same fellow who made some amazing observations while in the bath.

[nogreenthumb]

wow thats cool!

Will be interested in seeing if the members here utilise this principle, I saw it just recently on another Aquaponics site and they have also been discussing its uses.....

[Murray]

That is good, they are obviously on the same wavelength as we are.

[moet poep]

Give it a shot and see how well it works. You might be able to use a ground screw (used for holding down ropes) for your spiral. The fact that the casing can be joined to the screw suggests that you could make a very simple mechanism to drive it.

The idea of using it to lift fish is intriguing.

njh, can you please advise as to which one of the internal members is the impeller? I assume it's the one in the reduced conical section but want to be sure. thanks

[GaryD]

Hi,

njh has not been active on this forum for quite a while. Last I heard, he had moved to the US to work. His insightful posts are missed.

I'm still very interest in the use of axial flow pumps in aquaponics. Perhaps your query will revive the discussion.

GaryD

[moet poep]

Thanks Gary. What njh is saying is correct and the axial pump is the ideal pump for the AP water circulation requirements. It will pull in and push a large volume without the force in the flow that causes turbulence and back pressure that waste power and therefore the expense in energy bills. Plus it is simple to construct. (Murray should have some old propellers lying around.) Small fan blades will do. Plastic ones are easy to trim down to clear bore of tube and small low rpm motor to propel at closed end. If you think of a prawn pump with a fan blade rotating inside.
The rain has really set me back. When I get my concrete work done, I will knock up one and I'll post pics.

mp.

[GaryD]

Hi,



I will knock up one and I'll post pics.

We'll look forward to it. I'm not entirely enamoured with the idea of high revving little submersibles in the fish tank......and the CHOP arrangement often doesn't leave the tank as clean as I'd like it either......so something that moves lots of water without churning up solids, would be well worth considering.

Gary