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Old 02-13-2013, 06:25 AM   #24
AndreyT
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Quote:
Originally Posted by Aquaticfan View Post
Ummm No its not incorrect, Physics is still physics.
Precisely. Physics is still physics.

Quote:
Originally Posted by Aquaticfan View Post
Canisters work on a gravity fed siphon.
No. Canister filter has two siphons leading into it, which precisely cancel each other.

Quote:
Originally Posted by Aquaticfan View Post
A canister filter relies on gravity to feed and prime the filter to fill it with water. ... The pump does not create a vacuum - if it did, the canister would be capable of self priming. ...

Try this experiment.

Stand on a ladder or chair above your tank. Using a hose try to suck on the hose to create a syphon and pull water out of the tank....
This is all correct, but completely irrelevant. What I said before explicitly applies to an already primed filter, i.e. a filter whose canister is filled with water, both tubes are filled with water and the tube ends are submerged in the tank. I though I made it clear.

Quote:
Originally Posted by Aquaticfan View Post
If this was the case then a pump wouldnt even be needed all one would need to do is create a syphon and it would circulate.
No, you got it completely backwards. What you are saying (i.e. your claim that canister filter is gravity-fed) means that the pump is not needed. A gravity-fed system would only need gravity to work. I.e. if canister filter were a gravity-fed system, it would work as Perpetuum Mobile without any pump.

The reason canister filter is not a Perpetuum Mobile is exactly what I said above: the siphon effect from the intake tube exactly and precisely cancels the siphon effect of the return tube. The net effect is zero. This is why water will not move by itself through the filter. This is why you need a pump is a canister filter.

Quote:
Originally Posted by Aquaticfan View Post
It takes the weight of the water falling (this is caused by gravity as weight is a form of gravity and its pull on things) through the tube on the intake to create the syphon thus filling the canister
Again, this is only true for priming the filter. This is completely irrelevant to the operation of already primed filter.

Quote:
Originally Posted by Aquaticfan View Post
What happens if you get an air bubble in the intake tube but the canisters full? You get a canister filter that doesnt flow.
I'm not sure what you mean here. No, a mere bubble in the intake tube will not stop the filter. In order to stop the filter you need a quite large bubble in the intake tube. When you remove water form the intake tube, you create a disbalance between intake- and return-side siphons - the return siphon produces greater back-pressure that intake siphon. With large bubbles this disbalance might get large enough to overpower the pump. But a mere break in the intake water column (a bubble) will not be enough to achieve that. How large that bubble will need to be depends on the "pumping" power of the pump. It will vary from filter to filter.

Quote:
Originally Posted by Aquaticfan View Post
How does the syphon keep flowing? Falling water through the tube continously filling the filter so it can reach the pump.
I'm not sure what the point of this is, but anyway:

Pump has absolutely nothing do to with siphon operation. The water falls down through the long output end of the siphon. As long as the upper end of the siphon remains submerged, atmospheric pressure will force the water from the tank into the upper end of the siphon, thus ensuring continuous operation of the siphon.

Quote:
Originally Posted by Aquaticfan View Post
Raise the canister above the tank and the syphon slows to a halt.
False. This will not halt the flow. This will simply reverse the flow in the siphon (as long as the upper end of the siphon is submerged).

The only way to the flow in a siphon is to make sure water levels on both sides are equal.

If the water levels are unequal, the siphon will always flow from the higher level to the lower level (again, assuming that the upper end remains submerged).

Quote:
Originally Posted by Aquaticfan View Post
Why.. Gravity has less effect. Resistance is higher and cretaes a flow restriction on the intake. Volume in is not equal to volume out.
Sorry, this just makes no sense to me.

Quote:
Originally Posted by Aquaticfan View Post
As mentioned before Canister are unable to pump/create vacuum inside a canister to keep a syphon or start a syphon.
Again, absolutely irrelevant remarks that only apply to an empty (i.e. non-primed) canister filter. What they are doing here is not clear to me.

Quote:
Originally Posted by Aquaticfan View Post
They are PUSH pumps only. There is a reason why manufactures of canister tell you they need to be placed lower below the tanks for a reason.
That's false. One reason to place a canister below the tank is to ensure that it doesn't get siphoned out during water changes. If you place canister above the tank, then when you expose the return (or intake) tube during tank water changes, the water will get siphoned out of the tubes (and possibly out of the canister, depending on the design). Also the filter will have to be re-primed afterwards. To avoid this it is recommended to place the canister below or next to the tank, but not above it.

There might be other reasons, tied to the design of the canister, but none of them are relevant to the basic principle of operation of the filter.

Quote:
Originally Posted by Aquaticfan View Post
BOTH canisters and wet drys are fed by gravity and syphon effect.
False. Only wet-dry are fed by gravity. Which is rather obvious from the fact that wet-dry filter continues to be fed even if you unplug the pump. Meanwhile, canister simply stops if you unplug it.

Quote:
Originally Posted by Aquaticfan View Post
The only difference is the forces of atmospheric pressures between the two as the wet dry is exposed to such pressures and canisters are not.
That's false and actually self-contradictory. You can't have siphon effect without atmospheric pressure. It is atmospheric pressure that makes water rise through the ascending leg of the siphon. Atmospheric pressure always acts on the tank water. There's no way to "hide" from it.

Quote:
Originally Posted by Aquaticfan View Post
Canister filters are basicly a controled leak. Your creating a leak by means of gravity to flow down an intake tube fill a fliter and then get it to a pump that pushes it up a outlet.
That's exactly what wet-dry filter is: a controlled leak.

This is absolutely not true for canister filter. Canister filter is not a leak at all. This is, again, the fundamental principle that justifies the very existence of canister filters.

If you ever inspected a wet-dry filter, you should know that they use a significantly more powerful pump than canister filters. This is exactly because in wet-dry filter the pump has to lift water back into the tank. Canister filters, meanwhile, use relatively small impeller pumps. The reason canister filters can get away with such tiny pumps is specifically that these pumps don't have to lift water into the tank. All the canister pump has to do is to make "weightless" water circulate through the tubes.

Quote:
Originally Posted by Aquaticfan View Post
Lets look at the MAJORITY of designs of canister.. Where is the pump located? Before or after the filter media? MOST ALL if not ALL pumps on canisters are AFTER the media.
It is completely inconsequential where the pump is located in the canister filter. It can be located anywhere in the water path. The only reason it is located after the media is to protect the impeller from possible debris, i.e. to put the impeller into already filtered water.

Quote:
Originally Posted by Aquaticfan View Post
Using this method allows us to push out the air in the canister easier thus easier filling with water. It also allows for a Smaller pump to be used to get the job done if the pump is in the top of the filter at the outlet fitting as it then only has to force the water up the outlet hose. So a pump NEVER pushes the water through the media. It only pushes the water out the outlet hose.
Sorry, that just makes no sense. Regardless where the pump is located, one way or another it will always have to perform work of forcing the water through the media. There's just no way around it. Otherwise, it would simply magically defy all fundamental laws of physics. The work required for pushing water through can't simply come out of nowhere.

I will not comment further, since the rest is just getting repetitive.

Quote:
Originally Posted by Aquaticfan View Post
I know several Fluid Engineers
I suggest you contact them and have them explain it to you.

Last edited by AndreyT; 02-13-2013 at 06:41 AM.. Reason: Corrections
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