syphon overflow tubes with air bubble problem

[kurgen]

I am having trouble with the siphon tubes always getting air bubbles and thus reducing the flow of water back to my sump which in turn causes a low water level in the sump for my return pump which then pumps micro bubbles throughout my tank!!!
I have adjusted the flow rate of my return pump to compensate for when the rate slows but now I dont think I am getting the proper circulation
I prime the tubes so there are no air pockets in them and within a hour bubbles apear, there are no cracks or holes for air to enter them
My question is are there any powered ways or a DIY fix to this problem???
PEASE HELP

 

[squidd]

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...ieump 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

 

[kurgen]

thanks for your help squidd that makes perfect sense I have a magdrive 950gph for my return and the 2 x1" always get bubbles large enough to break the flow

 

[cain420]

try moving the ube around inside the overflow. mine is off to one side instead of in the middle and i get alot less bubbles.. i do get some, but not alot and they are small and pass right through.

 

[kurgen]

I am using 2 overflow boxs and have removed 1 1" syphon tube from each and they seem to be working fine I was even able to turn up my return pump a little to increase circulation
thanks again :jumping: :jumping: