External overflow for emergency backup?

[pegasus]

Okay guys, I need a little help. I can usually figure out little things like this own, but for some reason, I'm stumped. Let me start from the beginning. Early this morning, the power went off. It came on a couple of hours later, while I was at work. My wife was at home (fortunately!) and called to tell me that our 40B tank was overflowing. She was actually very calm, and I told her to open the gate valves on the overflow lines under the tank. She did, and the water level dropped... and the slurping from siphoning began. When I drilled this tank, I used 3/4" bulkheads for the dual overflows and return. I have dual 1" bulkheads draining my 125 gallon, so I figured dual 3/4" bulkheads would be sufficient for a 40 gallon tank. When I get the gatevalves dialed in, it is more than sufficient, and it's quiet. However, when I shut down the pumps for water changes (or other maintenance), I've always opened the valves on the 40 gallon in anticipation of it overfilling once I start pumping water back into the tank. I have thought about what might happen if the power was cut and came back when no one was home, but then would forget about it until the next time. Today was my wakeup call, and I need to get this fixed ASAP.

I really don't want to remove the fish, completely drain the tank, and remove the rocks and sand just to take the tank out of the corner it's in. It'll be virtually impossible to move it otherwise, due to how it sits down in the stand. I want to know if I can use an HOB overflow as an emergency overflow without it draining water all the time. If I put the top of the standpipe at the level I want to maintain in the tank, it shouldn't flow unless the water level rises. I'm almost certain that this will work, but wanted to know if anyone else has tried it. I'm looking for assurance...

 

[snakeblitz33]

If you prime the siphon on the external overflow and the actual tank itself starts to overflow, yes, it will do what it's supposed to do.

Post a picture of how the overflows are arranged, I'm kinda interested.

 

[pegasus]

Cool... thank for the confirmation! I have to order an overflow now. Here's a picture of the overflow and one of the gate valve. There's one of each one each side of the tank.
Not sure why the pictures got flipped, but you get the idea. I had initially drilled a 1/4" hole in top of the elbow in the bulkhead, and inserted a 1/4" RO line in it for a vent tube. That didn't seem to be enough, so I drilled it out to 3/8" and inserted the white tubing you see. I couldn't stop the slurping, so I attached air line tubing to the top of each tube and used a dual gang valve to control the air intake. It worked okay, but wasn't consistent. I capped the tubes and installed a Spears gate valve on each drain. This allows me to tune each drain so it doesn't siphon, which creates that annoying slurping sound. Once it's dialed in, I never have to touch it... unless I turn the pump off or the power goes out. It's strange how it's so consistent once it's set, but doesn't go back to that same flow after the water level drops. I don't expect the overflow box to cure this problem, but I deal with that later. I just need to be sure I don't flood my den, and burn up 4 pumps in the process.

 

[snakeblitz33]

Looks like a small hose for the drain!

If you set the external overflow on the tank rim and keep it primed. As long as it matches your pumps flow, you should be fine.

 

[pegasus]

It must be the angle, because I have 3/4" bulkheads, 3/4" elbows, 3/4" braided hose, and 3/4" gate valves. The two 3/4" hoses go through the floor, and just below the floor (in the basement), each hose ties into 1 1/2" drain which carries it to the fuge.

I use a Mag-Drive 9.5 on the 40B. It's not too strong due to the 3/4" check valve, 12' run, and 8' head. I used 45 degree elbows on all the turns, which helps reduce backpressure, and I estimate it to flow about 350-400 GPH at the tank. The overflow box I'm looking at handles 1100 GPH, so I think it'll be plenty big enough... lol!

 

[snakeblitz33]

If you don't pair the overflow box with the pump flow, it causes the U siphon tube to build up bubbles that aren't pushed through and end up cutting off the siphon and end up overflowing the main tank anyway.

I'd see how many gallons per hour are reaching the tank and pair the proper overflow with it. I personally like eshoppes overflows. They never failed me.

 

[beaslbob]

Adding an hob overflow as an emergency could be a problem to keep primed.

Your tank overflowed because water was pumped from the sump.

One of the adjustments is to fail (in you case block) the drains and insure the upper container does not flood. The sump needs to run dry before the flood. Then get things running normally again and draw a line to the sump and never never add water to the sump is above that line.

Finally, you could also try some kind of float valve but the is much more complicated.


my .02

 

[pegasus]

Snake, I'm looking at an eshopps 1100 GPH overflow, which is more than 4 times the flow of the pump if you also consider the two 3/4" overflows already on the tank. It might be better to match the flow, but I'd rather it be able to handle the flow and plenty more. Keep in mind the current overflows are draining water, but not at the same rate they do when things are stabilized. One thing that has come to mind is this: my 125 has no gate valves on the two overflows. When I cut the power for water changes, or there's a power outage, it fills to it's normal level and flows properly. I installed gate valves to slow the siphon on the 40B to get rid of the slurping (suction) noise. The flow from the tank is perfectly equal to the flow coming from the return pump... and almost exceeds the flow, so every once in awhile, there is some slight slurping. The main difference between the two tank's overflows (other than gate valves) is that the 125 has pipes that extend below the water line. The 40B drain is a couple of inches above the water line. I'm starting to think that the position, above or below the water level, has a big impact on drainage once flow has stopped and then resumes. I am going to extend the drain so it's submerged, and give it a test run. Hopefully this will cure my issue.

The reason I even thought of this is that I just remembered how the overflows on my 125 start slurping if one of the pipes (from the dual bulkheads on my refugium to about an inch below the surface) slips out. It gets really loud! This tells me that the flow has changed dramatically. I haven't tried a simulated power cut with the pipes removed on the 125, because it's always worked without fail. I may experiment some day just to see if it makes any difference, but even without trying, I'm almost positive that the 125 would suffer the same problem with overfilling.

If extending the drain below the water level doesn't fix the problem, I'll have to resort to an overflow box... or a float switch. Thanks for the suggestion, beaslbob. I actually like that idea better than the overflow, as it won't require monitoring or re-priming. Even if it cycles the pump on and off while I'm away, it'll provide a safety net and a chance to realize there's a problem without having to worry about flooding or burned up pumps. I'll let you know how it ends...

 

[snakeblitz33]

If your pump is underpowered, it will cause bubbles to be trapped inside the tube, causing it to lose siphon. With enough flow, it pushes the bubbles through and they don't get trapped. It's physics.

 

[pegasus]

If your pump is underpowered, it will cause bubbles to be trapped inside the tube, causing it to lose siphon. With enough flow, it pushes the bubbles through and they don't get trapped. It's physics.

Oh... you're talking about an overflow box with a pump. My bad. I was referring to an overflow that uses gravity to siphon. Yes, I'm aware that bubbles can get into the U and break the siphon, but I don't want the overflow to run all the time. I only need something to use as a backup when the tank overfills. I have the perfect flow with my current drains... when everything's tweaked.

You know how bean animal setups always have that one pipe that doesn't drain unless the tank overfills? My original goal was to use the entire overflow box as that emergency drain. The more I think about it, the less I like the idea of an overflow box. I ran out of time to test my drain extension theory. Hopefully I'll have time to try it tomorrow.

 

[beaslbob]

Again.

Have you considered adjusting the water level in you sump so that when the drain of blocked the display does not flood?