I'm planning to make this overflow for my tank. the goal is to drain from bottom.

in theory it will work but in real world i'm a bit worried about the noise that "air in" is going to make and where water level is going to be when power goes off.



There should not be any noise at the point that you have marked "air in", maybe just the sound of water trickling. It's vital in this design to have that unsealed air in point at the top, otherwise your tank will siphon and drain completely.

In the event that the power goes out, the water will not drain lower than the top of the pipe that goes to the sump.

My concern here is that your "water out" bulkhead has to be 100% sealed, otherwise your tank will empty. If you're able to, I would suggest rather installing the bulkhead higher up, at the lowest point that you would like the water to reach.

A different design suggestion

This design will still suck water from the bottom of the tank and won't siphon (as long as you have the air in opening). But, if your bulkhead springs a leak, won't accidentally drain your tank.

The other concern is that you will need to be certain that your drain works at least as fast as your pump, otherwise you will have overflow.

  • Thanks, sorry i don't have enough reputation to vote up you answer... – ElectronSurf May 16 '19 at 17:40

Yes, but there's a number of pitfalls with a system like this.

First off, it provides no redundancy, so if you clog your drain line, you're going to overflow your tank. Personally, I would never even consider running an overflow without redundancy.

Second, because it's a bottom drain, it will have a much higher risk of clogging and cleaning out the tubing is going to be very difficult. There's not an easy way of clearing out that trap, and since you're not running using a siphon, it will not self clear.

Third, noise may be an issue depending on how much turnover you are trying to get in relation to the size of the tubing. Generally speaking, running an overflow vented, you will want to shoot for less than 25% - 35% of the nominal flow rate to have it run quietly. So, for 1.5in PVC you'll need to shoot for something like 500gph, maybe less even, even though the gravity rating is 2100gph. Otherwise, you'll get gurgling or flushing sounds or constant water noise.

A quiet overflow is accomplished because you create annular flow around the entire outside of the pipe with an air gap in the center. It's nice and smooth and quiet. When you push too much water in it, the air gap collapses, and you get noise as the air spaces clear. However, I do not know how water would behave when it's entering the vertical pipe at a right angle, as in your design, your flow rate may be severely limited for quiet operation, or it may be completely impossible to keep it quiet. You may be able to circumvent this by increasing the size of pipe just before the second vertical section, or venting directly above the vertical pipe instead of the vertical feed pipe, but I'm just guess at this point. Air noise would be dependent on how you vent it, if just has an open pipe of the same diameter, I don't think you'll have any air noise, if you're trying to vent with small diameter tubing, you run a higher risk of air noise.

I think in theory the rough design would be functional, it may take some trial and error with your return pump and the tubing lengths to get the correct flow and water height in the aquarium. I think you are going to be dealing with some trial and error to get this to work the way you want it to. I would personally figure out some way to make this redundant though. Single drain systems are a insurance claim waiting to happen.

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