overflow siphon breaking after about 2 hours

[joelradding]

I built an overflow for a turtle tank and it works for a while but after about 2 hours the siphon fails. The inlet pipe is only about 5 or six inches from the bottom of the tank as there is a shallow water level. Here is a rough diagram of the overflow as an attachment in word. If I suck air out of the utube going over the tank wall the siphon starts up again and runs fine for awhile, but air seems to accumulate in the utube breaking the siphon. The inflow from the pump in the sump is next to the overflow but pointed away from it. However bubbles may be getting inside the overflow from the inflow and breaking siphon. Any thoughts on this to correct this problem and get the siphoning effect to be continuous?

[Mebbid]

I would hazard a guess at the problem being too low of a flow rate on the pump. When the flow rate is low air will tend to accumulate in the U bend.

That's the primary reason the HOB overflows aren't popular with the DIY version being particularly unpopular.

What's the diameter of the PVC and what's the flow rate of the pump?
What is your goal with the sump for a turtle?

[54seaweed]

the over flow tub depending on the length needs to be submerged at least half way with water from the bottom of the tub to maintain a good suction , any thing less will allow air to build and stop suction ,

[dylan p]

Can you show a picture of your overflow?


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[dylan p]

Oh now it let me click it. I would blame how far it has to climb before it falls because after it reaches the top of the tank it becomes more of a water fall then a siphon so I would think airs getting sucked in from the tall part on the back. Maybe put a cap on it with an air line coming out to lessen the amount of air that's able to get in? That would be my best guess. If not you could raise the water, gently blow air into the airline check valve to see if it leaks because they break pretty easily, cap the out put and the other end and blow air in it to make sure it's not leaking at one of the fittings. I honestly think the problem is the depth of your water or the check valve


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[joelradding]

Thanks for the input everyone. In reply to Mebbid's post, What are HOB overflows? Diameter of PVC is 3/4 inches. Flow is 60 gallons/hr. The sump is part of a trickle down wet/dry filter for turtles because I found commercially available filters and pumps inadequate or prohibitively expensive.
In reply to Dylan P. There is a word attachment with my original post with a diagram. I will try to post a picture if I can figure out how to do it from an iphone. The system seems to be working a little better with a a couple inches of water in a short 1/4 in tube coming off a $2.99 air check valve goop cemented into a 3/16th inch hole drilled in the utube going over the tank wall. Do you know where to procure decent self sealing air check valves for pvc? The inflow pipe is below the outside T fitting which has one branch leading to a trickle filter/sump and the other to a standpipe. Could that be a problem? Is the hole in the cap of the standpipe too small at 1/8 inch?