Overflow problem

[reefman5511]

I have a 45 Marineland gallon cube with factory overflow. The overflow will run fine for a bit & then start breaking the siphon making a gurgling sound that is driving the wife nuts. There is an air tube that comes with the the overflow but I'm wondering if I should move the position of it to let the air into the down turn.

Current overflow with air tube:

Here's where I'm thinking of moving it to. The upper one is the drain pipe:

 

[der_wille_zur_macht]

There shouldn't be an actual siphon with that sort of drainpipe, it's meant to be a mixed flow of water and air at the same time. Is the little black thing on the tip of the airline a valve? Have you tried playing with that? What sort of flow rate do you have from the sump? What diameter is that plumbing?

 

[reefman5511]

That's a silencer to cut down on the sucking sound. 1" pipe. Running a Mag 5 on it with roughly 4 ft of head.

 

[der_wille_zur_macht]

If it's siphoning, dropping the water level, breaking siphon, level goes back up, etc - over and over, that often means not enough air. I'd try adding a second piece of airline, or opening that one up to a larger size (ideally with a valve so you can adjust the airflow). Also, ditch the short piece of rigid airline and run flexible air hose - stick a few inches or more down inside the overflow piping, such that the inside end of the hose is down past the 90 outside the tank - fiddling with the position of the inside of the hose alters the point in the drain at which the air is introduced, which can help improve noise and performance.

One other thought - what's the other end of the drain line like, inside the sump? Is it underwater? How far? If there's lots of backpressure from the end being underwater that can make tuning hard when there's lower flow.

It doesn't sound like you're overwhelming this thing with flow, just probably one of those things where you will have to play with it to get it right. And of course a mixed flow drain like this will never be dead silent like a true siphon will.

 

[SkiFletch]

Yeah, having the drain vent exterior to the tank would be a little better. Likely you're dealing with salt creep issues somewhere in the air line itself, the little black valve/muffler-looking thing on top, or perhaps right inside the fitting where it meets the pipe. Moving it exterior would prevent the creep from blocking it up and give the venting you need.

 

[reefman5511]

I try to keep the sump end of the drain line out of the water to keep the back pressure low. I'm guessing that the air inlet tube is glued in since I could never move it. I'll try the suggestions when I get some time. Thanks.