Problem with siphon for overflow?

jagermeister

jagermeister

Member
It appears that for an over the tank overflow (one that's not drilled through the tank) everyone relys on a siphon.
My question is what happens when the power goes out? The return pump will stop pumping from the sump/refugium to the main tank. The main tank will drain down to the level of the overflow box. The siphon will suck until the water within the overflow box gets too low and then the pressure the siphon relys on to function is broken.
Now let's say in 10 minutes the power comes back on. The return pump starts pumping away. But now the siphon is not primed and not in working order, right? Are we looking at a big mess as the return pump pumps excess water from the sump into the main tank which eventually overflows?
Or is there such a thing as a self priming siphon?
 
cap'n pete

cap'n pete

Member
What you need for a U or J-tube style overflow is for both ends of the tube to remain under water even if the power goes out. Most overflows have dividers where the water remains. take a look at some pictures and you may see what I am talking about. Then, when the water comes back on, the siphon continues working. HTH
 
broomer5

broomer5

Active Member
Yep
Any decent overflow of good design will restart time and time again.
The siphon doesn't actually suck water - the water is pushed through the U tube.
It's not all the complicated really, but if this sort of thing bores the crap out of you - you may want to consider closing this now.
The atmosphere that surrounds the Earth, is held by gravity.
The atmosphere contains gasses, small particles and vapors.
Since it contains "stuff" it is attracted to and held by gravity - just as any other stuff on Earth is held.
Since the atmosphere contains "stuff" .. it has weight or mass.
All this stuff, gas molecules, vapors and dust press down on the Earth. It definately has weight.
At sea level - all this stuff weighs in at approximately 14.7 pounds per every square inch of the planet, including ourselves. You don't feel it - but the weight is there.
The higher you go up a mountain - the less atmospheric pressure or weight there is. The lower you go to sea level - the more relative pressure there is ... and eventually you're back at sea level .... and your back to the 14.7 psi.
Even very very small amount of change in elevation are measurable and cause things to happen.
In an external overflow - with an inner and outer box connected with a water filled U tube - the weight of the atmosphere is pressing down on the water in the inner and outer box.
When the pump's not running, and the water in both the inner and outer box are at the same level - the atmospheric pressure is the same over each box of water. 14.7 pounds is pressing down on the water in the inner box, and 14.7 pounds is pressing down on the water in the outer box.
Then the pump is turned on the the tank level begins to rise. As it does, the water begins to fall through the teeth of the inner box. Now this water level rises in this inner box a little. When this occurs - the head pressure of the water ( it's weight ) plus the 14.7 psi of the atmosphere is greater than the head or weight of the water + the 14.7 psig in the outer box.
This "differential" or difference of weight and pressure PUSHES the water up through and over the U tube - and it falls out the other end - and finally falls down into the sump drain.
Differential pressures - must occur for anything to flow up.
Sucking pop from a straw is the same thing.
The difference in pressures between the atmospheric pressure pressing down on the pop in the glass vs the lack of pressure in your mouth ~ causes the pop to be pushed up into your mouth.
The wind is the same - differences in atmospheric ( barometric ) pressure make the air "flow" from one area to another.
It's all about pressure - or the lack of pressure - and the difference between the two - that makes an overflow do what it does.
External overflows are not tug-of-wars. External overflows are not like two sides with a rope. They are two sides with a pole. The inner side pushes the pole to the outer side. Not pull.
Overflows do what they do because between the inner and outer boxes - there's a very slight difference in elevation - a very slight difference in head pressure and a very slight difference in atmospheric pressure. The U tube just happens to connect the two - and the water MUST travel up and over.
It has to. It's being "pushed".
It's pretty wild !
 
melbournefl

melbournefl

Member
ROFLMAO :eek: broomer dude, I'm sorry but your head just *MUST* be about to go *pop* from information overload. The only question I have is, does all this infomation manage to work it's way into making you any money? LOL very good explaination guy!
Later,
Paul
 
broomer5

broomer5

Active Member
Yeah Paul - my head goes pop often.
Sadly ~ as a small child - each day after school, I was duct taped to a bean bag chair, given peanut butter and jelly sandwhiches .... and forced to watch billions and billions of Carl Sagen and other public televison programs.
My only escape from this horrid treatment was to sit in the garage with a set of encylopedias - and my dad's Craftsman tools.
It was a nightmare - and I am the result of such an upbringing.
High School and College wasn't any better - for the damage had already been done at a young age.
I am a product of too much meaningless data, and my wife makes fun of me because I can't remember what cable channels ABC, CBS or NBC are on either :(
 
zafirablanca

zafirablanca

Member
Hi there,
I am setting up a 125 gallon tank with 2 Tidepool SOS (Silent Overflow Skimmer) overflow boxes. They appear to be different than the style that you guys are talking about here. I dont see a U-tube. It does have two hoses that drain to the sump for each overflow box, one called a flow tube, the other called the overflow tube. Has anybody used this type? Know anything about them? They were sold to me by the lfs.
All comments appreciated.
Thanks!
 
broomer5

broomer5

Active Member
Yeah zafirablanca
I looked at the TidePool at LFS.
He runs several for various tanks.
Nice set ups - not cheap at all.
These systems use the same principle of moving water up and over from one inner toothed box to the outer box.
It's just that their design does not use a traditional round tube bent into a U shape.
Theirs has a siphon tube too - but it's flatter.
Sort of a U shaped flat tube - sort of.
More like the CPR designs.
Exactly the same - but totally different LOL :p
 
rsd

rsd

Member
Broomer I think you and I had alot of the same early years... except that I chose the PBS channels. Still due today: Discover, TLC, History, and FOX (love seeing stupid people do stupid things). I too can spout of hundreds of useless facts that only I find interesting about stuff that most people find boring.
Physics still excite me 'cause it is always asking "why?"
 
danrw84

danrw84

Active Member
broomer...i could really use your expertese!
anyway..., i have a 29 gal reef. I want to set up a refugium. I can get the hang on CPR for 83 bucks, I ordered it, but now im wondering if i should do something differnt.
What would be involved for me to put a little 3 gallon glass tank which i already have, under my reef tank, in the cabient...and use that as a refugium. that way the 24/7 13 watt PC light wont shine into my tank, and into my room when its bed time!
what would i need to do? I have no overflows, and no clue where to begin.
Which would you recomend i do? In the 3 gal i wanted to put like a 1 inch sand bed, unless more is better, and some LR rubble, and some calerpa and other algaes.
How would i do a steady DOWNFLOW into the 3 gallon, then BACK up to the 29 gallon. I want pods and such to grow as well.
so, with no overflow, what would i do. How much would i have to spend?
Thanks in advance. let me know, or email me at danrw84@cox.net
anyone else with info please, let me have it! :)
 
cap'n pete

cap'n pete

Member
Hey Dan,
Go look at your other post. I drew a pretty picture.
{insert subliminal message here}
\Must buy Cap'n Pete's Overflows....gooooood....yes......//////
:rolleyes:
 
danrw84

danrw84

Active Member
is the venturi hook up on the oveflows from CPR necesary then?
what if air slowly fills the overflow then it stops the syphon,,,and the return keeps pumping
what happens then?
 
jjboods

jjboods

Member
The guy at my LFS...very knowledgable...says that if any overflow is likely to lose siphon it is the CPR because of it's design...tends to hold air pockets no matter what you do. He swears by the amiracle brand...about $65 for, I think, a 700 GPH flow...600 at least. So...that's the one I bought. I turn mine off and on all the time to do water changes and NEVR lose siphon.
 
bneal

bneal

New Member
I had this same concern, so I found a Quality batery backup for a computer on sale at a tech store $30. I did some math and my pump is about 25 watts. The battery will run a 300watt computer and 190 watt monitor for about 15 min.
If I am right, it should run my pump for over an hour.
The down side, is if the power goes out at night the damn thing beeps real loud.
 
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