Dual Drilled 1.5" Overflow Design Question - Fail Proof?

[Consigliere]

I'm working on the plumbing design for a new 240G setup. Using drilled back which will have two 1.5" overflows to a 70G sump and two 1.5" return lines. All piped with ABS. I have pics of what I think is my best overflow design option. The small hose at the top of the upside down P will allow for release of air to the standpipe side and also allow for water if the overflow is fully utilized. The return lines will all have 1.5" check valves. My question is does this cover all the failure modes of a tank (ie power failure), as long as my pump output never exceeds my overflow capacity (2500GPH I figure)?

 

[Pharaoh]

Looks good, but the extra "U" bend that you have in there might prove to be not needed.

 

[CHOMPERS]

You only need one return. And design it to not rely on a check valve.

Is the stand pipe going inside the tank or outside? And is it going to the sump or for the return?

 

[Consigliere]

The goal was to have one return line going to a manifold which will feed 3 lines. 2 returns to the tank and 1 to the house drain for water changes which will normally be valved off.

The overflow standpipes will be mounted on the outside of the tank and feed via 1.5" bulkheads with strainers to protect from fish being sucked in. They will be submerged which is the reason for the U bends in the plumbing. Don't want to hear the siphon sound of surface skimming.

Why stay away from check valves, other than that they can fail? How can you design a system that will not siphon if the pump is off if the returns into the tank are bulkheads way below the water level? The reason for 2 return lines is to create custom submerged spray bars for controlling water currents in the tank to minimize outgassing and create good convection water movement.

 

[frnchjeep]

I think that design could have a lot of bounce and could be noisy. Not sure though. Just a thought.

 

[CHOMPERS]

Why stay away from check valves, other than that they can fail?

If that isn't a good enough reason, I don't know what to say. The color, maybe? (Don't rely on anything mechanical when you don't have to.)

Run a loop to the surface and then drill a small hole just below the water to act as a syphon break.

 

[CHOMPERS]

The goal was to have one return line going to a manifold which will feed 3 lines. 2 returns to the tank and 1 to the house drain for water changes which will normally be valved off.

There's a better way of doing water changes, but if you want to do it that way, you will need a bulkhead fitting sufficiently below the surface so you can draw off enough water.

The other way of doing water changes is to set up a constant drip system. You will need to drill your sump at the max water level and set that to the drain. (You won't have to do manual water changes.)

The overflow standpipes will be mounted on the outside of the tank and feed via 1.5" bulkheads with strainers to protect from fish being sucked in. They will be submerged which is the reason for the U bends in the plumbing. Don't want to hear the siphon sound of surface skimming.

If the U's are not vented, then they will just be syphons (negating their intended purpose). The wate will drain to the lowest point and then start to gurgle.

There is another way of doing it that works really well. Make sure each pipe can handle the flow of the pump by themselves and then put a valve in the line of one of them. Inside the tank, the bulkhead without the valve will need a 90 facing the surface. Then throttle down on the valve until the water rises and overflows into the 90. You want just a trickle to go in. If the bulkhead with the strainer becomes clogged, the 90 will pick up the slack. It will also start to gurgle, alerting you to the problem.

...to minimize outgassing...

If this is going to be a planted tank with CO2 injection, you should consider a canister filter rather than a sump. A wet sump will work well, but a wet/dry will allow for off gassing.

 

[CHOMPERS]

...overflow capacity (2500GPH I figure)?

Figure on about 844 gph per 1.5" overflow.

I saw that the U's are vented. I don't think they will have a significant impact on the flow rate (minimal restriction).

 

[CHOMPERS]

If it's not already drilled, consider doing it something like this:

The two valves in the right loop(s) are for a 30% water change and completely draining the tank.

 

[Consigliere]

Thanks for all the great feedback and ideas here.

For the waterchange, I have no choice except to have a manual system for draining. The drain line for the house is far away so the drain from the tank had to run up through the floor joists, thus I need to power it to get any water out. Can't rely on good ol gravity here. The drip system was something I was going to employ. A drip into a refugium that I will setup to overflow into the sump. For water changes I will drain the refugium totally into the sump and refill with house water and let sit for 24 hrs minimum. The refugium will have either air stone or HOB filter as well.

I also do plan on having ball valves on each overflow and return line to have control over the flow from each pipe and to be able to shut off sections for maintenance or upgrades.

The siphon break is an idea I originally threw out because I didn't think it would work in this setup but now I think it actually may. My plan was to have the return lines at different heights in the tank, again for achieving good and controllable currents. If I put a siphon break on the inside of the tank on the top return will this break the siphon so that the bottom return (submerged) will not flood back to the sump?

The sump design is going to be a wet sump with lid to minimize off gassing.