removing an overflow box

[brianhellno]

bulkheads in the holes and run a canister filter through them. You could have the intake be flush with the bottom
I’m sorry, but hooking a canister up to tank bottom drilled, bulkhead fitting is just not a good idea.
The only way that even comes close to making sense is a shut off valve at the bulkhead fitting.
With a canisters main seal being a skinny “O” ring the chances of springing a leak increase at each service.
I have seen you mention this in a number of postings and have just shook my head in wonder.

Why would the chances of springing a leak go up with each use? From my understanding there shouldn't be any more pressure on the filter than if it were running up over the side. I thought that there's no real difference aside from the column of water above the filter is in the tank instead of running down the back in a tube. But other than that it should be the same PSI.

If I'm wrong can you please explain because I don't understand. I'm not trying to be confrontational I would just like to know how it works.

 

[KaiserSousay]

Canisters work more by siphon then pump.
The pump really just pushes water out of the canister and the siphon action refills it.
So there really is no “pressure” to speak off on the intake line.
Like doing a water change, you start a siphon and can hold your finger over the end of your tube and there is no real pressure against your finger.
Take that same line. Attach it to a bulkhead fitting on a vessel full of liquid. You now have the weight of all the liquid above the fitting against your finger.
With a siphon the water will come out in a stream, with the fitting it will come out as a jet.
“O” rings need to be soft enough to seal but hard enough for use. The more times you remove and press them into your sealing surface you cause wear. These rings actually expand and contract. They swell to seal. All this action causes minute cracking in their surfaces until they fail.
When a canister’s seal is breached, it usually will ooze. A small, slow drip to start. This will most often show when the canister is not running and the modest amount of pressure from both intake and return lines are being contained by the canister.
Take that same canister and hook it to a fitting with an amount of liquid sitting above that fitting and you are not just holding back the water in the tube, but all the water above the fitting as well.
Sorry if it seems confusing, really not when you really give it some thought.
That’s the best I can do as far as an explanation why yours was a bad idea.

 

[brianhellno]

Ahhh I see what your saying. That makes sense. I guess I always used the height of the water makes the pressure but that doesn't seem to to work with a syphon. Or at least there's different variables to take into consideration. Thanks I appreciate that you took the time to help me understand.

 

[Pharaoh]

I agree with there being excess pressure on the filter when plumbing through a bulkhead vs a standard siphon, but i wouldn't be positive that this would be detrimental to the filter or the seals therein. I have seen numerous setups where individuals have plumbed their tanks this way. To some extent, the additional pressure would help the pump as it would not have to work as hard to move water. If you fill the overflow with water, therefore having a completely full tank, I would think the pressure exerted on the pump/seals would be minimal.

 

[bob965]

So there really is no “pressure” to speak off on the intake line.
Like doing a water change, you start a siphon and can hold your finger over the end of your tube and there is no real pressure against your finger.
Take that same line. Attach it to a bulkhead fitting on a vessel full of liquid. You now have the weight of all the liquid above the fitting against your finger.
With a siphon the water will come out in a stream, with the fitting it will come out as a jet.

This is incorrect. If you have a bulkhead at the bottom of a tank connected to a piece of tubing, the pressure at a given point in the tubing is determined by the height of the water, plus the atmospheric pressure. If you then consider the same tank with a siphon tube going over the side, the weight of the water flowing up over the lip of the tank is offset by the same volume of water flowing down over the lip of the tank, and you are left with a column of water equal to the height of the water in the tank. The pressure at a given point in the tubing is determined by the height of this column, plus atmospheric pressure. The pressure in the bulkhead example will be equal to the pressure in the siphon example as long as you are measuring pressure from the same point, relative to the water level in the tank.

 

[brianhellno]

I agree with there being excess pressure on the filter when plumbing through a bulkhead vs a standard siphon, but i wouldn't be positive that this would be detrimental to the filter or the seals therein. I have seen numerous setup where individuals have plumber their tanks this way. To some extent, the additional pressure would help the pump as it would not have to work as hard to move water. If you fill the overflow with water, therefore having a completely full tank, I would think the pressure exerted on the pump/seals would be minimal.

So your saying that KaiserSousay is right as far as there being more pressure but your saying the additional pressure is okay and could be beneficial?

This is incorrect. If you have a bulkhead at the bottom of a tank connected to a piece of tubing, the pressure at a given point in the tubing is determined by the height of the water, plus the atmospheric pressure. If you then consider the same tank with a siphon tube going over the side, the weight of the water flowing up over the lip of the tank is offset by the same volume of water flowing down over the lip of the tank, and you are left with a column of water equal to the height of the water in the tank. The pressure at a given point in the tubing is determined by the height of this column, plus atmospheric pressure. The pressure in the bulkhead example will be equal to the pressure in the siphon example as long as you are measuring pressure from the same point, relative to the water level in the tank.

And your saying I had it right the first time.....?

hmmmm looks like there is some research to be done. I guess I'll start reading into this. Hopefully someone chimes in that either has one of these setups and can show some pics or somebody can give a demonstration or example that shows what's going on.

 

[Pharaoh]

So your saying that KaiserSousay is right as far as there being more pressure but your saying the additional pressure is okay and could be beneficial?



And your saying I had it right the first time.....?

hmmmm looks like there is some research to be done. I guess I'll start reading into this. Hopefully someone chimes in that either has one of these setups and can show some pics or somebody can give a demonstration or example that shows what's going on.

I'm just saying that I have seen it done and plan on doing it to one of my tanks in the near future. I just think that the seals would surely hold the additional pressure from the tank, with the rationale that they hold on the output side of the filter when it is on and pressure is created in order to move the water. I doubt that the seals would be designed differently from one side to the other.