How do you get rid of air in an overflow siphon tube?

[jeromefong]

I have an overflow with two 2 inch siphon tubes. I stick a small air tube inside the siphon tube to suck the air out and start the siphon. However, I am never able to suck all the air out. I also have bubbles around the overflow that seems to get sucked up into the tubes too. Eventually, there is enough air in the siphon tubes to stop the siphon.

Is there an easy way to remove all the air out of the tubes when I start the siphon? Also is there a different method for removing the air as it builds up in the siphon tube? Is there a way to put a vent or value on the siphon tube to get the air out?

Thanks,

 

[Len]

Jermone,

Let me move this to the General Reef Discussion for you to get more experienced ideas.

IME, it's normal to have some air at the top of the siphon. However, if the air pocket increases to the point where the siphon breaks, you definitely have a problem. This isn't normal. I am guessing there is too much air getting into the siphon intake. You'll have to raise the water level (or lower the siphon intake) somehow if this is the case.

 

[Anonymous]

Just take one of the tubes out. Air building up means the flow through the tube is not fast enough. If one 2" tube can't handle it try adding a 1" U tube along with the one 2" tube.

 

[danmhippo]

Did you connect the airline tubing to the venturi attachments for the powerheads? As long as the end of the tubing is at the highest point of the siphon tube, power heads should suck the air dry.

 

[Ben1]

Did you connect the airline tubing to the venturi attachments for the powerheads? As long as the end of the tubing is at the highest point of the siphon tube, power heads should suck the air dry.

This is only true for CPR overflows. For standard u tube overflows, Matt is right you just need more flow. The bulbs will fly thru everytime if there is enough.

I use a lifereef double that I think has two 1" u tubes that can handle 1500 gph total? I think so two 2" u-tubes would need alot of flow....how much return are you getting from the sump?

 

[jeromefong]

I have a surger returning the water from my sump. The surger is suppose to return the water at 400 gph. Does this mean the siphon tubes are too big?

thanks,

 

[Anonymous]

FWIW I put a airline connector at the top of mine with a valve to open or close it. I use an airline tube with the valve open and then suck the water up in the u tube. Then close the valve.

With good flow almost all the air bubles will be pushed through the U tube. but air can an does accumulate and sometimes break syphon. So I have to keep an eye on that.

I have not connected the connector to the input of my pump. But others have and state that it does work to start and maintain the utube syphon.

 

[Ben1]

Yes your return is to small, I would go with one 1" u tube with a 400 GPH return. Does the 400 GPH include head loss and loss for elbows and such, if not you are getting much less then that.

With a proper sized return/u-tube combo bubbles should never accumulate.

 

[Anonymous]

Ditto. Two 2" tubes is way too much for that flow. I had a very similar situation to yours a while back--30 gallon tank, two surge devices with approx. 900 gph of flow in the tank at peak flow. I had two 1" tubes and it handled it okay.