DIY filtration - Direction of Flow?

[Kalavek]

I'm considering design ideas for an out-of-tank filtration system for my 45g freshwater tank. I have noticed that a lot of filter systems pump the water through filter media from the bottom rather than from the top.

Why is this?

 

[epond83]

first thing that comes to mind is that the bigger particales want to settle on bottom so makes since to have the coarsest material the and pull water up to the tank.

 

[Lotus]

With overflow systems, the water leaves the tank from the top.

I'm not sure there's really a compelling reason that it has to leave the tank from any particular level.

 

[Chris_A]

So, correct me if I'm wrong. You're asking why the intake of the filter (on the canister) is on the bottom and the pump head is on the top? Best I can figure is to *possibly* save on ~1' of head pressure. Doesn't really make much sense though, canisters should work as a closed loop and most of the vertical head pressure should be negated because of the siphon effect. Basically that means they only have to push against the elbows and from the level of water to the top of the tank.

Really there is no reason I can think of that they MUST be bottom up filtered. Take a look at the Magnum line from Marineland, the impellers are on the bottom and intakes on the top. Another good example are any of the pressure canister filters (Red Sea and Pentair Aquatics are two off the top of my head). The big thing is just to take all aspects of a design into account.

Chris

 

[Kalavek]

So, correct me if I'm wrong. You're asking why the intake of the filter (on the canister) is on the bottom and the pump head is on the top? Best I can figure is to *possibly* save on ~1' of head pressure. Doesn't really make much sense though, canisters should work as a closed loop and most of the vertical head pressure should be negated because of the siphon effect. Basically that means they only have to push against the elbows and from the level of water to the top of the tank.

You're not wrong, that is what I'm wondering about. Also, my thoughts echo yours about cannisters being a closed loop... siphon lock = neutral flow. Pushing water up through filter media isn't specific to closed loop filters, however - epond might have it right, this may just be a case of heavier debris staying at the bottom.

I noticed the AquaClear HOB I purchased forces the water up through the filter media. I've also spotted some DIY wet/dry sump systems do this with passive flow instead of forced. TopFin filters avoid gravity altogether by having the water flow sideways through the filter.

I thought at first it might just be a gimmick or patent issue, but that wouldn't explain the DIY examples. If it had practical purpose, I would work it into my designs.