Closed Loop Help Needed

[alistair]

I bought a 90 gallon used tank that is drilled with three holes for a closed loop (1 output, 2return).
The problem is that the return holes are only 1/2". What do you recommend that I use as a external return pump?
I have a pump (can't remember make and model) that I use on my present 1" pipe closed loop. It is rated for 1200ghp, Is it possible that this may be to much pump for 1/2" pipe?

 

[JohnS_323]

Have you given any thought to making the holes larger? That might be an option to get the msot out of your pump. I'm not really sure much you can push through 1/2" pipe but it sounds pretty small to me.

 

[Baxreefs]

What size is the outlet, not 1/2" is it?

You could return your sump through the 1/2" holes

Feed your CL with an over the top siphon and return to a over the top manifold.

Or

Use the 1/2" returns plus an over the top manifold.

 

[alistair]

Outlet is bigger than 1/2". I think it is 1" I'll check when I get home.

 

[cmsurfr22]

the cross sections of two 1/2" pipes is less than the cross section of a 1" pipe, therefore it would not be a good idea to use that 1" pump. you if you are splitting the output of a pump the cross section of combined outputs should be more than the cross section of the pump's output.

remember: the cross section of a pipe is pi * r2 so:

Pipe Diameter
Cross Section


----------------------------
----------------


1/2"
3.14159 * .252 = .196


3/4"
3.14159 * .3752 = .442


1"
3.14159 * .52 = .785

​

 

[Baxreefs]

So, if it is 1" you could feed a 1" CL pump (I prefer 1 1/4+ for that but it will work) then use the two 1/2" ports plus like four more over the top and have a real nice CL

 

[alistair]

Now I'm confused ...
I have a 3/4" bulkhead piped to the 3/4" input of of the pump. The 3/4" pump output will be reduced and spit/ T'ed into two 1/2" return pipes.
Is this okay?
Is it possible to get a pump to big for this piping?

 

[cmsurfr22]

you can not squeeze a 3/4" down to two 1/2" returns because 2 * .196 < .442

in words...the sum of the two cross sections areas of your output is less then the cross section area of the output of the pump.

 

[Carlo]

ReefCentral.com has a Drain Size Calculator on the left side of the home page. Playing around with a few values found that 325 gph will require a 0.74 inch minimum drain pipe diameter for good results. BUT as cmsurfr22 already pointed out the 2 half inch "returns" aren't big enough to match the input. The velocity of the turn would be a lot higher (not really bad) but you will have a lot more resistance inline which isn't ideal.

The size holes you have available really sound better to use as part of your filtration system (sump/skimmer/return) then for a closed loop. Are the holes situated in a way that could be used for an internal overflow?

Another possible idea might be to use all three holes to feed your CL pump and do the return over the back of the tank as Baxreefs already suggested. You could get a little more volume that way without drilling the holes bigger.

Out of curiosity do you know what the original owner of the tank was using the holes for and what size pump he/she had attached?

Carlo

 

[alistair]

These holes were used for a closed loop run by a Little Giant 3 (700 gph)pump. I want to use GenX-XPC 30 (850 gph).

 

[Absinthe]

Even 850gph is a small amount of water movement IMO, uless your return pump is really hauling or you have powerheads.

I vote for enlarging the holes and using an even bigger pump than the one you have.

If you move those holes up to accomodate 1" bulkheads then your selection of pumps grows exponentially.

Another choice would be to enlarge the intake hole to 1" to flood the pump. Return the pump to a SCWD with 3/4" tubing, leave the SCWD with 3/4" tubing and cut it down to 1/2" at the entrance of the return. The SCWD will cut the flow down closer to 750gph.

Either way I think you need to make the intake larger.

The output can be fooled with...there are ways of bypassing a line (to the s ump, fuge, skimmer, over the back wall) and splitting the return if you need to.

 

[cmsurfr22]

i agree on enlarging the holes. i think this is the cleanest and best thing to do

 

[Baxreefs]

If you don't want to chance enlarging the holes, you can build a PVC manifold that feed the two 1/2 hoels and 2-3 3/4" out lets over the top back of the tank with five or more 1/2 to 3/4 inch outlets you could run twice the pump and distribute the flow more.