Why not a pump instead of an overflow?

[ppm411]

I'm going to upgrade from a canister to a wet/dry sump system. I've been doing all sorts of research on overflow boxes CPR, Lifereef, AquaCrylic etc. I'm pretty sure I understand how it all works now. However, why not just use a pump to get the water down to the sump instead of going through all of this? Is it because the suction would be to great and suck the fish out of the tank? If it's a matter of maintaining water level, couldn't a box with teeth could be placed inside the tank and the intake tube fed to the bottom of that box? It seems that this would solve all flooding problems I must be overlooking something obvious.

 

[rhomer]

You would never get the system properly balanced. The nice part about overflows is that the water going down can and only will be the amount of water being pumped up.
Rob

 

[ppm411]

I see. So even if I used the same exact pumps for in and out, it still wouldn't balance properly? I guess I'm still in the canister frame of mind because what I've described in the original post does exactly what a canister does only with one pump.

 

[oceana]

It will not work
IF and i mean IF you considered trying this you would need to have ball valves on both pumps. you woulkd have to adjust them so that both pumps put out the same flow. then you would also have to keep adjusting it as things got dirty to accomitate the slower pumping. IF you had the time to do this you would them have to figrue out what to do when one pump decides to quit working( of course this would be when your not home). this method is a quaranteed one way ticket to a flood.

 

[dea_mt]

yep gravity does all the measuring for you!!! ain't it beautiful!

 

[rhomer]

You seem to also forget that a pump on the ground pumping up 5 feet has a lot less head then a pump at the bottom of the fish tank. So you would at a minimum need a ball valve on the pump in the tank to reduce flow to the sump. This in turn would put a lot of back pressure on the pump and shorten the life span of the pump in the tank. Then the pump in the sump would continue when the pump in the tank would quit. Last you would overflow in the main tank once the pump in the tank quits. Followed by the pump in the sump overheating and quitting.
Rob

 

[ppm411]

Thanks for all the input. I am NOT going to attempt this since you guys have completely satisfied my curiousity.

 

[bob a.]

Originally Posted by ppm411
I see. So even if I used the same exact pumps for in and out, it still wouldn't balance properly? I guess I'm still in the canister frame of mind because what I've described in the original post does exactly what a canister does only with one pump.
But your canister is essentially acting as an overflow and a pump. Your pickup tube is the siphon into tank and your return line that is off the pump moves the water back. If for some reason the pump stops, you wont have a flood due to the continuous siphoning since the canister would be full and the water would have no where to go.
You need to design the system so that if power goes out, the water level in the main tank will drop to a point where it is below the lowest part of the overflow. Also, the water at that point should be no higher than the top of the sump tank. More than that and you have a flood.
Other things to take into consideration would be any water inlets (say from the main return pump or maybe from a separate pump servicing a uv sterilizer) should have some sort of anti siphon feature so that if they go below the level of overflow box they wont siphon out water and cause a flood. You can either have a check valve or it can be something as simple as a small hole drilled into the tubing at a high enough point to break the siphon.
Finally it is possible to have a flood if for some reason the overflow u tube or something else is blocked and the water level is pumped up in the main tank and has no where to go. Ideally, you should adjust the height of the overflow skimmer box so that there is a bit of room between the lowest tank level and the top of the tank. You wont have as much water in the system, but it will give you a margin of safety.
And if all this makes your head spin, then stick with the canister... :thinking:

 

[ppm411]

That all makes total sense. I've been reading a ton of material on some of the issues that people have had in the past. Now I understand why people think so highly of driling their tanks. Much like other people, I dont' have the courage to drill glass. I would really like to get away from the canister asap. Even though I do 10% water changes every week religiously I would like to include a refugium as another means of combatting nitrates. I would also like to increase the total volume of my measly 29g. Right now I have a 'hand-me-down- sump and some really old overflow box. So I'm going to invest in a new overflow and a new pump along with the tubung I might be missing to get things going.

 

[fixed]

Simpler is usually better. An overflow is far simpler than coordinating two pumps.
You know you can have an overflow without drilling, too? There are hang on overflow siphons.

 

[ppm411]

Yes, hopefully I'll be purchasing an overflow box in the near future. There is much debate on which is the best but I think I'm going to go with a CPR with an aqualifter vacum to insure a continuous siphon (Hopefully) Nothing is perfect.. Seems that drilling is the only way to guarantee there is no disaster.

 

[peter1215]

Originally Posted by ppm411
Yes, hopefully I'll be purchasing an overflow box in the near future. There is much debate on which is the best but I think I'm going to go with a CPR with an aqualifter vacum to insure a continuous siphon (Hopefully) Nothing is perfect.. Seems that drilling is the only way to guarantee there is no disaster.
let me know how the cpr box tunrs out . I am using an old overflow box with a U tube and was considering switching to a cpr .