Over Flow Box Nightmares! Post’em if youve got’em

[LowKey]

I’m receiving mixed signals about overflows as I read through the threads here on Reef Central. Some people like them, and others want nothing to do with them. I personally picked one up (hasn’t been delivered yet). It’s seems to be a convenient way to add a sump to any system without disturbing the aquatic life.

I’d love to read your thoughts and stories.

One last (beginner) thing: How does one prime an overflow?
:rollface:

[Jeremy Blaze]

I assume you are talking about a hang on the tank overflow box. Most likely one with a j tube.

Couple thiungs, First, you'll want to modify the j tube so you can have an airline tube on the top of it to pull the air out. You can use this to prime it, and also, if you run this hose to the venturi fitting on a powerhead, this will keep it running.

Do a search for this mod.

Keep an eye out for snails making there way into the j tube.

Do not put any type of filter material in the box.

[Konadog]

Keep the J tube clean and free of algae. This is overlooked most of the time, and over time the water flow slows down. This slow moving water allows air to start to collect, then the siphon will not keep up the the water input to the tank. This causes your tank to overflow, and give HOB overflow boxes a bad name.

[CEO]

If you dont mind me asking. What is the point of an over flow?

[Jeremy Blaze]

To ffed water to a sump.

[sjm817]

There is no reason to modify a (J) U Tube with an air nipple. A properly set up U tube overflow does not accumulate air and will run indefinitely without a siphon break. I run dual U Tube overflows and dont have any issues what so ever. They never accumulate even a single air bubble. As long as you get a decent box (dont get a CPR!!) and have the proper size return pump, there is no problem. Adding an airline just puts in a problem that wasn't there to start with.

Keeping the U Tube clean is a good point. I have a couple of sheilds I hacked together quickly to keep most of the light away from them.

[LowKey]

How about Weirs such as the one illustrated below?
http://www.melevsreef.com/acrylics/overflow.jpg

No tubes just a contained overflow. This to me looks like a better system. No?

[sjm817]

No.
That is basically the CPR design with the C channel that goes over the top instead of a U Tube.

Here is the problem with that design. A U tube overflow will not accumulate any bubbles at the top as long as there is sufficient velocity to blow the bubbles through. Use the correct size return pump, and you have a reliable system that will never break siphon.

The C Channel is wide and flat. The water moves slowly through it. It is impossible to have sufficient velocity to keep it free of accumulated air. The CPR band-aid fix is to put an air nipple on the top and attach a vacuum pump or powerhead to constantly pull out accumulated air. Something that is totally unnecessary on a U tube design. A pump failure or (as in my case) air nipple clog is a disaster waiting to happen.

[LowKey]

Just a thought, would a float switch connected to the return pump be the answer?

Place the switch within the suction area of the over flow. If the water level is lost, the switch will trip the pump therefore stopping the flow all together. The worst that can happen is your air system starts to suck straight air, which will cause a tremendous amount of air bubbles in your display tank.

[jreefer]

I have the CPR. There are some advantages to the air nipple. If the power goes out you will lose your siphon on your tube and on the cpr for that matter. But when the power goes back on and the pumps kick in, the little hated air nipple connected to the aqualifter pump restores the siphon and you have no flood. Without it, as in the other tube designs, here comes the mop...

[russ49merc]

sjm817,,,,, good points i have no problems with my HOB model it works great.

[Konadog]

Originally posted by jreefer
I have the CPR. There are some advantages to the air nipple. If the power goes out you will lose your siphon on your tube and on the cpr for that matter. But when the power goes back on and the pumps kick in, the little hated air nipple connected to the aqualifter pump restores the siphon and you have no flood. Without it, as in the other tube designs, here comes the mop... Not true for all HOB J tube models. If it is designed properly, you should never loose prime in the J tube when the power goes out.
Lets take the picture posted by LowKey, lets make an assumption that the overflow is the J tube, (I think the drawing is a CPR model) see how there is an area in the outside box that will always have water in it, that will keep you from loosing prime. If that is not tall enough, it will not hold enough water to keep both ends of the J tube under water and you will have a problem.

[rtbm]

I have said it before but having to rely on the aqualifter for the cpr to keep my floors dry is, after one failure already causing me to loose my hair even faster. I keep a backup just in case it happens again but knowing what I know now I would not have got it.

[sjm817]

Originally posted by jreefer
I have the CPR. There are some advantages to the air nipple. If the power goes out you will lose your siphon on your tube and on the cpr for that matter. But when the power goes back on and the pumps kick in, the little hated air nipple connected to the aqualifter pump restores the siphon and you have no flood. Without it, as in the other tube designs, here comes the mop...
A U Tube overflow retains siphon with no air pump required during a power outage. Both ends of the tube are submerged. Nothing is needed to restart the siphon since it is never lost. Only the CPR boxes need the pump to start a siphon.

[sjm817]

This shows how a U Tube overflow retains siphon with a baffle design. Some use a tall stand pipe instead of a baffle.

http://reefcentral.com/gallery/data/500/71647utubeon.jpg

http://reefcentral.com/gallery/data/500/71647utubeoff.jpg

[CrackerFish]

I am a believer that a well designed overflow/sump is unlikely have an accident. Worst case is to burnup your return pump. My sump is designed like this:

My overflow can handle more water than my return pump can deliver. So once the system is equalized, the only water out to the sump is the water that goes back to the tank (volume not the actual same water).

1. If the return pump fails, water will still flow of the tank until the level is equal with my skimmer box. At this point no more water will flow to the sump. I have extra capacity in the sump to handle this extra water in the event of pump failure.

2. If the OF loses siphon or becomes clogged, I have my return pump sectioned off so that there is only a small volume of water there at the pump. Once all that water (which is not much) has been pumped up to the tank, the only risk is burning up the pump. BTW there is extra capacity in the tank for the extra water.

This is just my opinion/belief based on my limited experience.

Just so you know, my sump is constructed from 2 19Qt plastic tubs.

Later All!!

[waterlily]

When I had my (non-drilled) 29, I made two overflows for it using U tubes and specimen boxes along with some plumbing parts. They worked like a charm. I was afraid that this would lose siphon, so I used a float switch mechanism on the return pump. The idea was that if I lost siphon, the pump wouldn't burn out for lack of water. Actually, the float switch worked great - but the only time it was needed was if I forgot to top-off and water was running low in the sump.

If you use a properly designed overflow (like the above model), you never have to worry about too much tank water going to the sump. If the return portion of the sump is limited so that it only holds as much water as can be pumped up without overflowing the tank if the siphon is lost, you don't have to worry about a tank overflow. MAKE SURE YOU DRILL A SIPHON BREAK ON YOUR RETURN PLUMBING!!!

[sjm817]

Yup. Good points. Mine is set up the same. The sump return section and display is setup so that one can not overflow the other if something did go wrong.