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double your filters flow rate


r.d.m

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ive just cleaned the filter on my african tank and noticed a gap of about 30cm between the top of the cannister and the bottom of the tank,so i put a small bucket upside down under the filter so raising the cannister to see if the flow increased and b***er me it DOUBLED!!! due i assume to the lower pump head ,so as long as the pump is below the intake you can optimize your flow!

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What the?!

While Im not doubting that your flow rate increased dramatically, I was under the impression that canister filters, being that they are closed systems effectively have no head pressure. Furthermore, that if they are put under head stress they blow up (bit like me in that respect really LOL.gif ).

All that the canister pump must do is move the water through the filter medium and the pipes. Could it be that your newly cleaned filter/pipes or the shorter hose distance is responsable for this change? dntknw.gif

If not, is there an aquatic engineer out there that can help with my education as a non-physicist. confused.gif

-worm-

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im not an engineer either, and dont fully understand what happened, i didnt shorten the hoses,i did clean the media and replaced the floss though,but the filter is now running much faster than it was new,could it be something to do with the fact it has different diameter inlet and outlet hoses?(pressure/suction differential) i would guess that being higher the pump would be pumping a shorter distance,but now running the same spraybar in the same place i have a big wave hitting the front glass and now for the first time since setting up the tank 6 months ago the water is crystal clear and the fronnies are far more active,can someone explain whats happening,maybe try it yourselves?

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I think you already did explain it RDM, just smaller head height.

The pump doesn't have as much gravity to push the water up against, because the vertical portion of the hoses is now shorter.

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Yep, that's correct it's all about head. If you shorten the lift distance from pump to outlet the volumn will increase as the impeller doesn't have to "work" as hard so it is able to spin at a higher rate, increasing volumn . If you also shortened the inlet and outlet pipes that would give a marginal increase as well, as you are effectively decreasing the resistance within the tubes. The longer the supply tubes the greater the turbulance within them, and turbulance = resistance.

glenn

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Im still confused confused.gif

Am I mistaken then in thinking that being a closed system a canister filter has no head pressure?

The pump doesn't have as much gravity to push the water up against,

Surely the effect of gravity acting on the water in the "in" pipe cancels out the effect of gravity on the water in the "out" pipe.

Also when the pump is off, the water level in the pipes remains the same. If there was head pressure then the pipe should backflow such as what happens in a sump (open) system when the power is turned off.

No pressure, no backflow was my understanding:dntknw:

-worm-

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G'day Worm,

A sump system has one main difference, a physical air gap, so equalization doesn't come into the equasion. I agree that when the canister is "off" there is usually no movement because both the inlet and the outlet are below water level, so the pressure equalizes. However when the pump is running the inlet water is "sucked" into the canister and then through the filter media by the "pushing" action of the impeller to force the water up the outlet pipe. The longer the outlet pipe, the more lift is required to transfer the water. That's why when you buy a pump they are rated in LPH at ground level, the higher the lift the greater the LPH drop. So you have to take the "lift" into consideration when you workout how much you need turned over per hour. Hope that makes it a bit easier to take in. thumb.gif

glenn

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cheers Glen, sort of makes sense but I think Ill stick to ecology, answers are a little less concrete more open to interpretation! wink2.gif

-worm-

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lol...well, i decided last night that i'm going to shorten my hoses and put my cannisters up on some bricks......It Worked!!!!...my flow rate increased considerably. Prior to this i was disappointed with the flow rate on my OTTO but it is really good now. I seriously don't know why i didn't set them up like this in the first place. Thanks for the prompt RDM thumb.gif.

Anthony

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If a person has a pump, plumbed to the bottom of a tank, inlet and outlet both plumbed in via bulk head fittings etc.

It is my understanding that the pump has no head to deal with due to the fact the water is pushing the water to the pump, so any head the outlet of the pump has to deal with is equalised by the water pushing out of the tank to get to the pump.

I am sure if one raised a canister filter higher, you would get better flow rate due to there being less head for the filter to deal with (I set my garage tanks up with this in mind). But how does a pump plumbed as above differ from a canister with and inlet and outlet?

Would it be due to the water having to get up and over the sides of the tank with the canister? And somehow this make the difference from a pump plumbed directly into the bottom of the tank?

Tricky stuff this water.

Craig

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when shorting your pipes on your canister should they be just long enough (like tight fitting) or have a little slack or it doesn't matter

The longer your pipes, the more friction you will have and the slower water flow you will have. However, you need to be able to move the filter a bit, so having the pipes a net fit may prevent this. Seek a compromise thumb.gif .

I'm going to answer my own above question. I checked it out with a mate, and after discussion I have taken on board that a canister filter plumbed via walking sticks has NO head to deal with as the water flowing out will level with the return pipe to the tank.

Turn off your filter, and look to see where the water level in your return pipe settles at. Wether this return end is emersed or immersed the water level in your return pipe will equal the water level in your tank.

Reddevilman, I think you must not have cleaned your filter for a long time laugh.gif .

Craig

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Craig, my experience with cannisters tells me I can't believe that.

If you turn the filter off, all hoses will be full. The inlet and outlet wont level to the tank level as there is nowhere for air to enter the system.

Explain how a cannister does not have any resistance based on 'head'?

As far as I can see, water enters the unit only because water is pushed from the unit via the pump. If this was not the case, in a power outage, water would keep flowing through like the overflow/siphon on sump based systems, the 'in' would not stop running until it hit reason to stop (ie. no water)

There is no free flow in a cannister filter - it is all suck and blow.

I may be reading entirely wrong but dntknw.gif ??

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Craig, my experience with cannisters tells me I can't believe that.

If you turn the filter off, all hoses will be full.  The inlet and outlet wont level to the tank level as there is nowhere for air to enter the system.

Explain how a cannister does not have any resistance based on 'head'?

As far as I can see, water enters the unit only because water is pushed from the unit via the pump. If this was not the case, in a power outage, water would keep flowing through like the overflow/siphon on sump based systems, the 'in' would not stop running until it hit reason to stop (ie. no water)

There is no free flow in a cannister filter - it is all suck and blow.

I may be reading entirely wrong but dntknw.gif ??

If for example you had a spray bar above the water's surface, then air will get in, and you will see that the water level will equal the water level of the tank. Just because no air gets in dosn't change the issue with head.

I should add too that a siphon hose does not need the help of a pump to get out of the tank - once it goes (eg. sucking), it's own weight pulls it from the tank.

If you get a clear hose, siphon water out of a tank, fill it up, then pick the bottom end up so it is just a bit above the level of water in the tank, with the beginning of the siphon still kept in the tank.

Gravity allows the water to level the water in this pipe to equal the height of the water in the tank (excess will go back to the tank). Head hight is any water above this point. Any water movement beyond this point requires a pump to push it.

For example, if you want to take water from a sump back to the main tank, the pump is either emersed or in line with the sump. Any water pumped past the water level in the sump is the head the pump has to deal with.

A canister filter is really just a siphon hose with a canister in the middle, turn the power off and the water level on outlet side of the pipe if any air gets into it, should equal the water level of the tank. The pump is there to push the water back into the tank from this point. It doesn’t need any help to get the water to the level of the water level in the tank, but needs it to get it past the water level of the tank, and over the edge of the tank.

The same principle will apply to the siphon hose going into and out of the canister as will the water level in the siphon hose as explained above.

Can't get these silly quote things to work.

How'd I do with my answer?

Craig

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There is no free flow in a cannister filter - it is all suck and blow.

Ducksta,

try turning your filter off, take the outlet out of the tank (or inlet for that matter if both are submerged), and lay it on the floor.

BTW - have the towels ready tongue.gif

Craig

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OK cheers, now I understand better Craig thumb.gif

I understood that the water entering the unit balances the water being pumped out - but didn't understand what you meant with the water level of the tank to the top of the elbow being the only point of any real 'back-pressure'

Ducksta,

try turning your filter off, take the outlet out of the tank (or inlet for that matter if both are submerged), and lay it on the floor.

BTW - have the towels ready

I don't use cannisters any more for this very reason. But seriously, what I meant with the suck and blow thing, is that flow is very much controlled by the pump when set up, obviously if I unplugged the out hose, it would have a free flow.

I still believe that lifting the cannister to reduce the height it has to 'push' the water has an impact on flow rate, it is something I experimented with. Although 'double flowrate' would be a massive exaggeration I think rolleyes.gif

ps. Craig, to work the quotes, you need the (QUOTE) before the (/QUOTE) tags. Obviously I changed the bracket type to demonstrate.

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I can usually do the quotes Ducksta, it just didn’t seem to like me this time. My fault I know, but I stuffed around with it for a bit, then ran out of time, and didn’t give a stuff… cryblow.gif .

I still believe that lifting the cannister to reduce the height it has to 'push' the water has an impact on flow rate, it is something I experimented with. Although 'double flowrate' would be a massive exaggeration I think

Yes, I know what you mean, thinking it through would make you think this. I think it might be truer to rather than say “push the water” (to the tank’s water level), to say “assists the water”. But when you take into account, this assistance will be equalled by the water coming back into the barrel, it’s a bit of a “push-me-pull-you”.

All I think you are doing is assisting the siphon, the pump still has to deal with getting the water higher than the tank’s water level.

Perhaps others could do some tests and let us know what happens.

BTW, though a hassle to clean, I love cannister filters. thumbup.gif

Craig

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Ducksta,

I checked it myself. I had a canister filter, no media inside. I placed it on the floor, one metre below the water level, and raised it up to the water level's surface.

I could see NO difference in the water flow. I raised and lowered it half a dozen times and I could see nothing alter.

Craig

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Well mine must have something to do with shortening the hoses rather than me propping up my filter, because something made it dramatically increase to a volume it has never ran at before.

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