How far can an external pump suck from?

[Krish]

I wanted to add some more flow in my tank. My question is this. If using an external pump (eg. something similar to the little giant pump) can I place the pump under my tank in my stand and it function properly by sucking water directly from the tank (about 4ft-5ft up). I know all pumps are not the same, but on average, if it cannot suck from that distance, what's the maximum distance an external pump can usually suck from.

 

[les]

One thing you may not know is the pump recommendations for maximum suction head is how high it needs to suck to get the water to the pump. When the pump is located below the water intake for it, this is not an issue. The only thing that would fall into play here is that total head loss through the pipes, 4-5 feet is not enough to worry about.
Good luck

 

[dnjan]

In general, placing a pump below the water level of the source of the water (water level in the tank for a closed-loop, water level in the sump for a return, etc) is no problem. The impeller-type pumps we generally use in aquariums work best when they are pushing water, not pulling it. The more you are pulling water (creating a vaccum), the more likely you are to get microbubbles in your return stream.

Please clarify what you are trying to do. Will your intake go up, over the top of your tank? Or is your tank drilled for the intake below the water surface? (or is this just a larger return pump?)

 

[Krish]

Sorry about that. My tank is not drilled and what I'm trying to do, or thinking about trying to do, is mounting an external pump inside of my stand (not in a sump or in any water) and suck water directly out of my tank, let the water run through the pump, and then back into the tank for extra flow. My tank is a 90 gal and right now I'm pumping 1600 gal/hr. I want to increase it to atleast another 1500 gal/hr to catch a few possible dead spots. Thanks.

 

[dnjan]

You may have a bit of a problem getting the pump primed. Impeller-type pumps won't pull enough of a vaccum to get water up and over the top of your tank unless the pipe between the tank and the pump is already full of water (primed). Yes, you could probably do it, but this is not a very robust system. If you lose you prime for any reason, it will be hard to re-start.

Unfortunately, you may be stuck with either using an overflow to siphon water out of the tank into a reservoir (a sump) and then using your pump to return it to the tank, or using a submersable pump (or powerheads) in the tank.

 

[Krish]

Alrighty then. I guess I'll have to think about it a bit more before I go ahead and do anything. Thanks for the info.

 

[dnjan]

Any way you can get your tank drilled? Acrylic is easy. Glass is best left to somebody with experience.

 

[Zephrant]

If you put a Tee at the top of the tank, with one side capped off, you can remove the cap to reprime the pump when needed.

You only need to reprime when the water level in the tank drops below the input, letting air in to the pump feed line (say on a water change).

It won't break prime otherwise, as the suction of the pump will pull though any small bubbles that try to accumulate. So it normally works well.

Drilled closed loops are great though, if you have a way to do it.

Zeph

 

[Krish]

Thanks Zeph. I think I might just give that a try

 

[CurvBall]

Sounds like you're setting up a closed loop. Much better than loads of powerheads inside your tank.

 

[Krish]

Yep, that is exactly what I'm trying to do.