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Discussion Starter · #1 ·
I'm planning on building a new Geoff skimmer for a larger tank (65 gallon) I will be setting up. I've built a 30" Geoff skimmer before and it worked fairly well, however, I'm planning on building one ~48" tall out of 6" pvc and there are a few questions I haven't been able to find answers for. It'll either be run on a mag 7 or 9.5 and have a kent 1/2" venturi or 3/4" venturi. The pump will be located in the sump and dump straight into the display so everything going into the sump will be run through the skimmer.

Due to the height, head loss may become quite significant. Instead of 3/4" pvc on the inlet side, would it be better to use 1" or 1.25" pvc? This would necessate using a larger outlet pipe but I can work with that. I ran some numbers through the head loss calculator on RC and with 4' vertical, 2 90 degree elbows, and ~7' head loss due to the venturi, I'm already very close to the shutoff limit on the mag 9.5. The head pressure would be about 12' and the shutoff is 15'. This would be a flow of about 220 gph and I was hoping for a little more. Am I way off in my calculations or will I need to get an external pump to power the skimmer?

Any thoughts or suggestions would be appreciated.
 

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why a 6" skimmer that tall? something that big i would actually do a Mag 12 with 2 3/4" ventur valves.

with a skimmer that tall, i would actually put the inlet pipe low on the skimmer. i would also point the inlet tube inside the skimmer body upwards towards the top of the skimmer. that way the the newly inputted bubbles would have a harder time getting to the outlet tube. it is a good idea to keep the head pressure on the pump side of a venturi as high as possible. this is very important with such a high head pressure you are thinking within the skimmer.

G~
 

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Discussion Starter · #3 ·
The reason for making it so tall is because I wouldn't mind eliminating a pump from the system. I was thinking 6" merely because I could and have some laying around. I could just as easily go 4" if that would work better.

Correct me if I'm wrong, but with the inlet towards the bottom, wouldn't you need a larger sump to compensate for the water volume in the skimmer when power is lost?

The skimmer on your website is about 40" tall, at what height do you think it's necessary to increase the pump from a mag 9.5 to a 12?

Thanks
 

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yes, you would need a bigger sump to handle the extra water in the skimmer. depending on how the inlet is designed, there still could be a significant amount of increased water volume going into the sump. the inlet tube can act like a siphon, even with a venturi on it.

i forgot that skimmer was that tall. :D it is not really a necessity to go to a bigger pump. with such a large skimmer it would allow more water volume to be processed. looking at the pump curves for the a pump can give you a good idea on when to up a pump size per skimmer height. a venturi valve tends to add about 7' of head pressure. so if you want 250gph through your skimmer, than a Mag 7 would only work up to a skimmer that has a reaction chamber that is less than 3' tall.

a Mag 9.5 would work for your situation, but i would think dual venturi's on a Mag 12 would be better. that is if your overflow can handle at least 500gph.

G~
 

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Discussion Starter · #5 ·
Thanks for the comments. It's given me quite a bit to think about.

I'm pretty sure I'm going far into left field with this one, but what about diverting some of the flow from a closed loop to feed the skimmer? There would be substantially less head pressure to pump against. The drawback would probably be that it would eat up much of the flow from the closed loop and negate the usefulness of a closed loop.

A mag 12 with two venturi's would be quite a bit of fun, although I wonder if 4" pvc with a mag 9.5 might be more practical. Lots to think about. Who am I kidding, I'll probably try 6" pvc and if I have to redo it out of 4" I'll be out maybe $30.
 

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the beauty of PVC is that it is fairly inexpensive. 6" can get expensive, but if you use uni-seals it can be easily done inexpensively.

if you try and run the skimmer off of a CLS, than the CLS will no longer be closed. you will really have to make sure that the tank will not siphon out through the skimmer. it would be better to use seperate pumps for each.

G~
 
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