J-tube vs. Contin. Siphon overflow

osueyedoc

osueyedoc

New Member
quick question guys & gals,
just wondering what everyone's opinions are on these two very different siphon/overflow box designs.
cpr's continuous siphon design with a venturi powerhead is intriguing, but i'm worried about powerhead failure and overflowing potentials.
i've also heard lots of people say they've run a j-tube design for years and years with no problems...any brand recommendations? i've seen lots of people recommend lifereef.
thanks for any info.
 
squidd

squidd

Active Member
I like the J or U tube overflow design because there are no moving parts/pump which open doors for mechanical/power failure to cause an overflow...
A properly setup U tube...with the ends deep enough to be submerged when power is out will maintain its siphon indefinitely and restart flow when tank side level increases.
The only caution (and this goes for the "box" type overflows as well) is that you need to size the U tube to have enough flow velocity to push the air bubbles through the tube so they don't build up and slow/stop siphon.
 
dreeves

dreeves

Active Member
LifeReef makes a fine overflow...you can also look on ---- they have pretty decent ones there for bid..
 
osueyedoc

osueyedoc

New Member
squidd,
what do you mean by "sizing the U-tube" for enough flow? do you mean picking the appropriate size overflow box?
The overflow i buy will go on my 75 display and drain to the sump in the stand, only about 4 feet or so. my return pump is a mag 950, so I was considering the single drain lifereef which i think is rated for 6-700gph.
any suggestions are welcome, you won't bruise any ego here.
thanks.
 
bigmac

bigmac

Member

Originally posted by osueyedoc

cpr's continuous siphon design with a venturi powerhead is intriguing, but i'm worried about powerhead failure and overflowing potentials.
.
You have read the recent threads here about the CPR's failing and flooding floors, right?...This isn't something that's just starting to happen with these overflows. Its been happening with them every since they came out.
I bought my first wetdry about 18 years ago. It came with a U-tube type overflow. I use it for ten years without a single failure.
 
squidd

squidd

Active Member

Originally posted by osueyedoc
squidd,
what do you mean by "sizing the U-tube" for enough flow? do you mean picking the appropriate size overflow box?

A lot of the complaints/questions about U tube overflows refer to the "bubbles" building up in the top of the tube...which if left to accumulate can slow flow enough (or even break the siphon) and cause an overflow...
The "cure" or prevention for this is to have the water flow through the tube "fast" enough to draw the bubble with and not build up.
This has to do with volumetric efficiency at a given flow rate...ie:pump rating minus head loss=given flow
Lets say the given flow for your pump is 700gph...
You can flow it through one 1" tube (fast), two 1" tubes (slower in each) one 1-1/4" tube (some where in between) or one 2" tube (very slow)...
The larger the tube the slower a given amount will flow...
(thats why the CPRs build up air and need a pump)
The smaller the tube the faster a given amount will flow...
(within reason, too small and it won't keep up)
So by changing the tube size/number you can adjust the speed of water through the tube at a given flow rate...
For example on one of my tanks at it's flow rate...one 1" tube couldn't keep up with return pump...two 1" tubes kept up with pump but built up bubbles...I switched to one 1-1/4" U tube and it keeps up with pump and flows fast enough to draw bubbles through.
Sizing the U tube to a given flow rate.
HTH
 
osueyedoc

osueyedoc

New Member
squidd,
thanks for the excellent description...i totally understand what you mean now. with your info, here's my proposed set-up:
lifereef prefilter...comes with a 1 1/8" ID siphon tube flowing at an average of 700 gph.
mag 950 return...which is rated at 800gph @ 4' and 750gph @ 5'.
i figure by the time i plumb from my sump to the tank (which is in the stand beneath the 75) i should be somewhere close between 4' -5' of head.
from there i'll decide if i need to modify my u-tube.
one more quick question...do you recommend placing a ball valve on the drain pvc pipe/hose? i understand that the return pump determines the flow rate, so will i get into some messy adjustments by adding a ball valve here?
THANKS AGAIN for all of your advice...it's exactly the info I needed that i couldn't find on any similar posts.
 
reefsoe

reefsoe

Member
only thing I will add my 2 cents in on is the fact that its a greeat idea to drill a small hole at the top of your return a little bit under your normal water line... If the power ever goes out the return line will suck water back into the sump.... and eventually overflow. By putting a small hole at the top of the line under the water surface it will break the syphon preventing a possible disaster.
 
squidd

squidd

Active Member
You shouldn't "need" a ball valve on the return line for "adjusting", but it is a good idea to have one to close off the overflow line should you need to remove the line from the sump for maintainence or whatever...
However, if the overflow is grossly oversized you may need to restrict the flow to maintain proper water levels in the chambers and to eliminate "gurgling" noises...
There are other options for that as well though, such as a "Durso" or "Stockman" overflow pipes.
 
midwest reefer

midwest reefer

Member
does the CPR overflow require a pump... I am planning on getting one, I didnt know it required a pump... :help: :notsure: :thinking:
 
squidd

squidd

Active Member
Midwest: CPR requires a pump to maintain siphon.:nope:
Indy: a "well stocked" LFS should have U tubes and straight acrylic tubes of various diameters...If not there are some "on-line" stores that distribute "catalogs" in which you will find them.
If you can't find the "premade" version, but can get ahold of acrylic tubes, you can DIY by filling them with sand, heating the tube till you can bend it, and then cooling it in water to "lock" it in shape...cut to legnth.:yes:
 
midwest reefer

midwest reefer

Member
will just any pump work for the CPR? I have a 125 gph powerhead just sitting around... will this work for it? sorry, i dont mean to intterupt the thread...
 
squidd

squidd

Active Member
Any PH/pump that has an air line "inlet" should work The venturi effect on the pump "sucks" air from the CPR keeping it from building up and disrupting the siphon...
Although I don't know if a 125 would have enough suction/pressure to work effectivly.
 
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