Siphon Overflow Myths?

[Anonymous]

2 overflows would be better with 2 feeds to the sump. A second U-tube reduces internal water velocity to low levels. Is this a DIY job?

How would this change anything? The same problem would develop. It's not a DIY job, I just added a second U tube to a prefabricated overflow.

f internal box and external box height is the same then how do you get siphon? Can't happen. That is the physics behind siphoning. What you siphon INTO has to be lower than the source. The lower it is the more pressure is generated and the higher the flow rate.

Look closer at your overflow- better yet take a ruler and measure the differential distance between the internal and external box. Mine is about 1/2.

You know the little wall in the external box that keeps water inside so the U tube stays submerged? As long as the height of that wall is within 1" or so of the top and bottom of the internal box, the siphon will work and not break. Lower that wall an inch, and the water level in the internal box lowers an inch as well. Raise it, and the same thing happens. Either way, you've got that very small difference (OK, I guess it's not the EXACT same level, but mine is closer to 1/4")between the water level in the internal and external box. This difference is constant no matter how high or low that wall in your external box is, and the height of the wall will not change the amount of flow through the tube.

 

[Anonymous]

BTW, if you have a removable standpipe in your external box, try it. Put a piece of PVC in that is taller than the divider wall by an inch or so. The water level in the external box will raise a bit higher, but the overflow will still work at the same capacity.

 

[xrunner123]

2 overflows would be better with 2 feeds to the sump. A second U-tube reduces internal water velocity to low levels. Is this a DIY job?

How would this change anything? The same problem would develop. It's not a DIY job, I just added a second U tube to a prefabricated overflow. .

Actually I take that back, a bigger pump and 2 overflows would be better.
See the problem with just adding a second U-tube is that the velocity basically cuts in half and this is where the problems with air come into pla-can't clear it. Now if your first U-tube was just too small for the return pump then yes a second U-tube will work. Maybe we are just on a diff frequency here.

You know the little wall in the external box that keeps water inside so the U tube stays submerged? As long as the height of that wall is within 1" or so of the top and bottom of the internal box, the siphon will work and not break. Lower that wall an inch, and the water level in the internal box lowers an inch as well. Raise it, and the same thing happens. Either way, you've got that very small difference (OK, I guess it's not the EXACT same level, but mine is closer to 1/4")between the water level in the internal and external box. This difference is constant no matter how high or low that wall in your external box is, and the height of the wall will not change the amount of flow through the tube.

This is correct. I never said that standpipes won't work- I have one also. I said that they shouldn't be all the way to the top as to interupt the siphon. Sorry for the confusion

 

[xrunner123]

Just to clarify a little more-

Let's say that your standpipe is 1" from the top of the waterline. And like you say you lower it 1" then the internal level lowers also by 1". So it basically follows the 1/2 or 1/4" delta as in your case. This is absolutely correct.

Now, if air get's in the line that delta will grow. If you are within 1" of the top there is not alot of room left, so you can get to a point of no return where there is too much air in the line and it can't be cleared- you just don't have enough water in the sump and height in the tank.

This is the reason why standpipes can cause problems. I have a midget one so there is always a 5" drop into the internal box, so when/if air gets in I have the umph to clear.
:wink:
Make sense?

 

[Anonymous]

Well, I can say for certain it's difficult to explain 3 dimensional objects over the internet with words... :wink:

The difficulty with adding a larger pump along with a second overflow is this: A larger pump, when returned through a surge device, will not alter the total maximum flow delivered to the tank by the surge device. It will only decrease the time between surges.

My original point was that there are some cases where a tank can flood with an external overflow box, regardless of the sump design. I believe it would be prudent to drill a tank whenever possible or to go sumpless. Even if you have a standard tank with a small pump area in the sump AND a float switch to turn your return pump off, in the event of a loss of siphon your tank will have no water circulation.

 

[sstephen]

Xrunner:
Thanks for the LifeReef link. I checked out their prefilter box design and was able to see what you meant. I was wondering, though, if you or anyone else happens to know the correct size ratios for the various parts? The Lifereef version is a bit too big for my aquarium (20G nano). I could simply use similar dimensions, but at 2/3 or 1/2 the size.

Just to clarify, the chamber in the external box where the water exits the U-tube should be able to hold enough water that, in the event of a power failure, the water level will rise to the same level in the internal box. This stops the flow (assuming that the actual tank level has dropped below the fill line of the internal box). If the flow is stopped while both ends of the U-tube are still submerged, then the siphon will be maintained and will restart automatically when power is restored. Did I get all that right?

 

[Anonymous]

Exactly. I actually turned the pumps off on a tank for several months once, and the siphon maintained itself.

 

[liquid]

marked for archiving

 

[larrylwill]

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[larrylwill]

I built most of my equipment about 7 - years ago. One of the first was a DIY overflow of my own design. Its still going. I would rather have drilled the tank but I couldn't find anybody to drill it and I was afraid. Now its filled. It was published for years at the Eastern PA Reef Club but looks like their not there anymore. The box is on the inside I designed one with PVC pipe and a minnow box. I made a u tube out of 2 sizes of PVC one inside the other. 1" with 1/2" inside, very small. I cut down the side of the minnow box that creates a top skimmer. there is NO noise at all from it. and keeps the surface very clean. It has been going for all of the 7 or so years. It did overflow on the floor a couple of times. I then added a float switch in series with my pump, so it it clogs, the pump shuts off. I use a small power head to pump water from my sump, with an adjustment on the output. I would rather have a drilled tank but this works just fine. I have to restart it maybe once or twice per year due to a snail or some other thing stopping the flow. I just use my skimmer output to blow back and release the air out from where it enters the sump. It was very easy to build. I use it on a 55 gal. I also built my hood and 2 - 175w MV bulbs taken from an outdoor fixture. I use 2 -40w actinic 03's for supplemental lighting. I still have the plans somewhere, if anybody's interested. It can be scaled up or down.

 

[liquid]

Hi larrylwill and

Shane

 

[larrylwill]

Hi larrylwill and

Shane

Thank you