Why do I need an Overflow?

[Dewman]

Rothie, I think (believe it or not) that I might be able to answer this one.

I'm not a mathmatician, but I think if you know the diameter of the tubing, say 1" ID, you can take the diameter, multiply it by the length of tubing, multiply that by pi(squared) ... maybe something like this.

(DT X LT) (pi squared)= Volume (V)

The acceleration of gravity is a known constant. The density of saltwater is also a known. unfortunately you will have to factor in the resistance caused by friction. I think it is probably something like 1GPH for every foot of tubing. So , If acceleration of gravity is (Ag) and resistance is R, and Mass of water is M... You would end up with something like this...

{(DT*LT)(pi squared)} {M} X Ag = Velocity

Of course, I am a bit rusty on all of this, so if anyone else has it ...

Maybe it would be better just to tell him :lol: :wink:




Of course, you could always just start out with a larger diameter hose and adjust the teeth up and down in the skimmer box. A friend of mine is using 1" and he is pumping back out of the sump with a 1200 GPH pump. Of course he has all sorts of elbows and 4 feet of head pressure working against him...

 

[Rothie]

Wow,Dewman,that was quite a bit to take in. Actually I think I need a more simple explanation.I'm still trying to find out how I figure the flow rate into the sump!I'm hoping someone can put it into perspective for me.

 

[Anonymous]

Dewman-Thank you so much for asking that question. I have been reading about overflow boxes for 2 weeks and seemed to be missing the point.I now have a much better understanding of why the siphon is kept during a power outage.

Vitz-that was a wonderful explanation of how the double box works.

Now I have a question. What determines the flow rate through the box and into the sump. I have a 15G reef, and I only want to have between 100 and 200 GPH flow.

Thanks for all the good info.You guys are great!

with a typically available purchased box setup, the determining factor should only be the flow rate of the pump that moves the water from the sump back to your tank-gravity and the return pipe just let whatever you pump up, to fall back down at that rate.
when your choosing a pump-look at the chart that shows flow rate at the 'head' height you're dealing with-that's what you're looking for.

 

[Rothie]

vitz-Thank you so much. I think I'm really beginning to understand how it works!

 

[Anonymous]

Rothie-your welcome
a couple tips-flow rates listed by manufacturers are usually a bit over optimistic. in actual practice, things like pump wear and tear, true i.d. of the tubing, etc. usually mean a slightly lower flow rate, though the difference is prob'ly not critical.
make sure the sump is sized to also acommodate the extra volume of water that WILL get added to the sump during a power failure(or anytime you need to shut off the return pump).remember- the tank is gonna drain down to the level of the skimmer box in the tank!
if your pump is too high a volume and you want to throttle it down, allways valve the output side-never restrict the inflow of a pump.HTH

 

[Rothie]

OK,vitz.Just one more question for now.I'll probably use flexible tubing from my overflow box to the sump. Is it necessary to keep the tubing above the sump level? I read somewhere about it causing back pressure if it is below the sump waterline.
Also, should I use a smaller diameter U-tbue on the siphon since I am only going to flow between 100 and 200 GPH,or is it better to use the 1" diamter U-tube?
I lied,that was 2 questions.
Thanks again.

 

[SPC]

Rothie, if I might interject something here, yes you can run the overflow hose under the water of your sump. Having said that you are probably going to experience what many have no matter if it is under water or not, bubbles being returned to the tank. There are different designs for DIY bubble traps on the boards but most of them involve running the hose into a bucket or other container. You can probably do a search on this topic and find a design you like.
Steve

 

[Rothie]

Thanks for the info,Steve.I'd much rather gather information before than after.I've read a lot about bubbles and baffles. The bucket idea sounds pretty simple. I'll do some searches.
By the way,why is it that we don't want bubbles in a reef tank? Is it just asthetics, or is there a mechanical reason?

 

[Anonymous]

spc- thanx for the reminder
rothie-the overflow boxes usually come with ribbed hose(looks like swimming pool hose- i think that's exactly what it is!)
the way i got around the noise issue with the return hose is to lay the hose end so that the water spills out onto a large filter foam (sponge) block- it acts as a noise 'baffle',and also helps reduce the amount of bubbles introduced into the sump.
for the pump- if it sucks air from the surface of the sump,take a 90 degree pvc elbow,place it over the intake pointing down(make sure the downward facing end is raised a bit from the bottom(!)).
also- if you get noise from the overflow box when the water spills down the ribbed hose(this may stop on it's own, as the loop balances out), you can take a small length of airline tied at the top of the box,placed into the hose,this will help the water 'cling' to the wall of the hose as it enters, reducing noise.
danmhippo gave y'all an excellent piece of advice when suggesting you take a look at 'em setup at your lfs-seeing it makes it alot clearer!

 

[Anonymous]

stay with the large diameter u tube provided, and check it occasionaly for stray air bubbles if you go the route of the double box overflow.
air bubbles in the tank are to be avoided, not just for aesthetics, but also because they can 'pocket' in your rock, kill sponge, etc.

 

[Rothie]

Thanks,again. I can see how the bubbles would impede the use of the overflow.I just found a DIY overflow box on the Library page that looks like it fits the bill.Any comments or suggestions are appreciated. Here is the link http://www.reefs.org/library/diy/diy_winner1.html

 

[Anonymous]

Thanks,again. I can see how the bubbles would impede the use of the overflow.I just found a DIY overflow box on the Library page that looks like it fits the bill.Any comments or suggestions are appreciated. Here is the link http://www.reefs.org/library/diy/diy_winner1.html

personally, if you allready have the tank, i'd recommend against this route and buy a ready made unit from amiracle. or some such company.
the lee's boxes are THIN plastic, flimsy, and easily breakable.a thicker unit made from acrylic is safer, sturdier,and will last you much, much longer. they should cost from about 40-60 bucks new,(if my memory is accurate).you should also be able to find some used ones cheap if you hunt around..
i used to knock my overflow around alot, when doing routine maintenance, etc.,and smashed the homemade box on a 20 gal setup!after that, only sturdy stuff for me :wink:

 

[Rothie]

That's what I call sharing your "experience". Really useful. Thanx.

 

[SPC]

I used the Marineland overflow (I think it is the Tide Pool) for about a year and never had a problem with it. Very quiet, easy to set up and never lost siphon.
Steve

 

[Rothie]

My tank is only 15G(24X12X12) and has a DSB. I havn't been able to find a manufactured box that is small enough for my tank.I thought the Amiracle would be small enough, but the inside box measures 6"X2"X6".Besides being obtrusive,I don't have that much room to spare.I found a place called jmkdisplays on the internet that will make custom acrylic overflows. I'll call Monday and see what they can do and give me a price. I"m only going to use the box for 6 months to a year, so I really don't want to spend a lot of money on it.I may try a few DIY's just for the experience-I'll keep the wet vac handy.I think I'll go to HD and browse.
Thanks so much

 

[esmithiii]

OK,vitz.Just one more question for now.I'll probably use flexible tubing from my overflow box to the sump. Is it necessary to keep the tubing above the sump level? I read somewhere about it causing back pressure if it is below the sump waterline.

There is no "backpressure." Whoever wrote what you read is wrong.

Good luck. I also recommend buying a manufactured overflow box instead of a DIY.

Ernie

 

[Dewman]

esmithii...

True, there is no back pressure, but perhaps whoever told you that, meant that there was a back-syphon.

Rothie... You will have to do some adjustment to the outlet head to prevent water from syphoning back to your sump pump when the power is off. Some people have used a one way valve, but those can get clogged and will eventually stop working.

The best way to prevent back syphon, is to drill a hole into the side of your outlet head just below the waterline created when power is on. When the pump goes off, and the water has drained into your sump to the point where the hole is exposed, it will break the syphon and prevent disaster.
This is the best way,so far, I have seen for stopping this.

I'm not sure if some pumps are equipped with something to prevent back syphon. My Mag Drive is NOT. Found that out the hard way last week.
But the drilled hole in the outlet works every time.

 

[Anonymous]

But the drilled hole in the outlet works every time.

Except when you forget to clean off the coralline that encrusted over the hole.

 

[Dewman]

True...

Does coralline grow on silicone?
Maybe you could smear a bit of silicone around the hole to keep this from happening :?

Not sure if that's a solution though.

SKBok, you've actually had it grow over a hole with water coming out of it? I have it inside the outlet nozzles, but I would think with 700 GPH of water coming out of the sump through the heads, and part of it coming out the hole, this would keep it cleared off. Mine is on the back side away from the light, maybe that's what keeps mine clear.
Hmm? I guess I learn something new every day

 

[Anonymous]

Yes I did have it grow over the hole, maybe it just wasn't large enough to stop the coralline intrusion. Just took one time to make sure I cleaned it out every couple of months.