air in my overflow

[nate9]

I started up my 55 gallon system last night, and ran into some previously undiscovered issues. This is my first system with a sump and I relized, dispite planning it for the last 6 months, I had no idea how to actually get it all to work (getting the flow from the overflow right, starting the overflow ect.) After a visit to Melves Reef I got my overflow started but ran into a big issue. when the water flows into the overflow from the display tank a small number of air bubbles make it under the bubble trap and up to the top of the bend in the overflow. These bubbles then build up over time up in that top section of the overflow and create a bunch of traped air up there which then reduces my flow to the sump and thus screwing up the system. I really dont want to have to suck the air out of my U-bend once a day so are there any solutions to this?

Also I started thinking about how many things could go wrong with the system and cause major flooding and am looking for preventional measures I can take to prevent:

- If the power goes out the return pump is rendered useless but the siphone continues which will cause too much water to flow into my sump (although this isnt that big of an issue since the siphone will only continue till the display tank water level gets below the overflow box inlet and my sump can handle that water wihtout overflowing)

- If too much water evaporates and the water level goes below the overflow inlet but the pump continues then my pump will run out of water to pump and burn out. Just vigilance to prevent this one? along with an autofill system?

Thanks

[nate9]

siphon**

[jedheuer]

one thing maybe that your return pump might be too weak thus reducing your flow through the overflow box. I have bubbles running through my siphon tube but they do not accumulate because the flow is strong enough to pull them through with the water.

To prevent overflows make sure the level of water in your sump is low enough to accommodate all the water when the power goes out.

And yes to the last question. You must add water to your tank everyday or eventually your pump will run dry. Get an auto top off from aqua hub.com I recommend them and they are cheap.

[nate9]

I think one of my problems is that I dont simply have a U-tube that the water is running through but rather its the whole unit. Here is a picture of the exact design of my box (not the same dimensions)

http://www.f3images.com/IMD/aquarium_images/overflow_box_cpr_dimension.jpg

[mille239]

I agree with jedheuer; You need to match your overflow with your return pump: Too powerful, you will pump water into the tank faster than the overflow can return it to the sump. Too weak: not enough flow going through the overflow, and air will accumulate in the top, eventually breaking the siphon, flooding the tank.

One other option is to tap the top of the siphon "u" with an air hose, and connect this with a small aqua-lifter pump (aqua bee?), constantly pumping a small amount of water through the air-line into the outside of the overflow box, that way any air that accumulates in it, will be pumped out.

Good luck.

[nate9]

I dont really understand this explanation. sorry. How does the return pipe not putting enough water back into the display cause air bubbles in my overflow?

[mille239]

Hi Nate. The weaker your return pump, (i.e., the slower water is returned to your tank) means water going through the overflow back to your sump is slower. The overflow only returns water to your sump at the same rate and volume as the pump in your sump is pumping it back to your tank. There is almost always some air bubbles traveling through the overflow, and if the current isn't fast enough to carry these bubbles all the way through (i.e. up, across, and then down against gravity) they will accumulate in the top portion of the "u".

if you increase the velocity of water traveling through the "u" (i.e. increase the return pump size) the bubbles are wisked through the u-tube faster, and cannot accumulate at the top.

I hope this makes it a little clearer. If anyone else can chime in and add anything to this, please do so!

[nate9]

I have ball valves on my my overflow down to overflow; would decreasing the flow rate of my overflow in order to match my return pump have the same effect has increasing my pump to match my overflow?

[mille239]

unfortunately no. All overflows are rated for a certain GPH range, (i.e. 400-600 gph) and going below that range will almost certainly lead to an accumulation of bubbles. A quick fix you can do is put some foam in the overflow (prior to the water going through the "u" portion" which will soften the water splashing in from the tank, and reduce the bubbles that will enter into the "u" portion. This will likely accumulate detrius, so frequent cleaning will likely be necessary, but should help to some degree.

[nate9]

so the only solution is to get a strong pump/ lower rated overflow???

if that is true then why is it not posted all over the how to set up a sump threads that your overflow has to be exactly the rate of your pump??? haha. I was told the exact opposite: that my overflow HAD to be rated higher then my return pump. i guess im reading the wrong threads =P

[jim.l]

From the pic you have a CPR overflow, or one designed like it. No matter how much water you move, you will still collect bubbles in the overflow. You should have a vent pipe in the top of the siphon and need a suction source such as an aqua lifter pump to pull water and the air out to keep it running.

[mille239]

Check this out:

http://www.cpraquatic.com/pdf/CS100.pdf
especially points 7 and 9

[nate9]

yea its not a cpr but very similar design. It actually has a vent hole with air line tubing already drilled and attached on the top of the U part. I though this was to aid in getting the siphon started but maybe its for a pump. how do i set up this pump-siphon apparatus?

[nate9]

mille239 that article was fantastic! Explained everything. thanks to all for the help. much appreciated. looks like ill be investing in a aqua lifter pump.

[nate9]

one final question: how do u prevent back siphon on the return pump line during a power outage? That article mentioned a check valve but what is that?

[mille239]

You're welcome!

Check valves generally should not be used on return lines. the best idea is to place a small anti-siphon hole in the return line just below the water level inside the tank, so as soon as the tank back-flows to this small hole (1/8 in is plenty) it will draw in air and break the siphon, stopping further draining of the tank.