Flow Rates???

aftrhrs

aftrhrs

Member
When I bought my 75gallon tank it came with the CPR Overflow Model #CS 102 which has the dual 1" bulkhead outflows. I just went to the CPR website and they rated this overflow unit at 1400gph (good for a 250 gallon tank). The biggest model they offered had the exact same dimensions as my overflow box except instead of (2) 1" Dia. pipes it has a single 1.5" Diameter pipe and it was rated at 1600gph. Now, since the area of a circle is equal to pie X the diameter squared, the 1.5" pipe is almost a quarter inch bigger that the two one inch pipes so I completely understand how it gets more flow. My question is, why can't I drill the unit I have for (2) 1.5" diameter pipes so I would have a theoretical flow rate of 3200gph. Then, when I upgrade to a 265 gallon tank next spring, the outflow box will not be my restriction. I will only have to upgrade my pumps. Does this sound feasible? I am going to go home tonight to make sure I can cut for bigger bulkheads but thought I would run it by everyone else. Anyody done this before??
 
aftrhrs

aftrhrs

Member
The 1.5" bulkhead looks wider but the angle that the picture was taken at is not the same as the angle for the unit I have which gives it the appearance of being a lot wider. I went to the website and they sell a single 1" bulkhead unit and it looks wider than the one I have. I little camera trickery is all :)
 
broomer5

broomer5

Active Member
If I remember right - the area of a circle is pi*r-squared
If so
A single 1" diameter ID pipe would have;
1.00 " ID
r = .5"
.5 x .5 =.25
.25 x 3.14 = .785 square inches
Two of these 1" pipes would equal 1.57 square inches.
A single 1.5" ID pipe would have;
1.5 " ID
r = .75"
.75 x .75 = .5625
.5625 x 3.14 = 1.766 square inches
I don't know if you can do what you plan to do - without problems.
Maybe you can maybe you can't.
In addition to the size of the drainline opening, the flow though the overflow can also be somewhat limited by the size shape of the U tube, and the actual volume of the inner and outer boxes.
If the one you have is rated at 1400 gph - with the two 1" drainlines - then by drilling two 1.5" holes/bulkheads would allow more water to drain - but I don't know if will allow more water to flow through the U tube.
Even if it did - you may find that trying to run 3200 gph ( .89 gallons per second ) through the device - may not work.
I just don't know for sure .. interesting idea for sure - and I'm looking forward to hear from someone that has actually done this before.
Would be cool if it works though ;)
 
aftrhrs

aftrhrs

Member
DOH! I put diameter squared, I meant radius squared your right. I still had the same answer, close to 1/4" more area. I will do some measuring tonight. Thanks for the input.
 
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