Maximum drain flow through a 1 1/2"
 

I just purchased my return pumps and now I'm starting to think it's too much flow for my drain to keep up with.

I bought 2 of these Rio 32hf
The flow is 1500gph at 4' head so I'm looking at 3000gph draining through a single 1 1/2 drain. I have another 1 1/2" for emergency and I don't want any flow returning through that.

I will have ball valves on the return lines so I can dial them back but was hoping to get maximum flow through these and avoid adding more powerheads.

The head loss calculator and overflow size calculator on RC are really valuable for figuring this sort of thing out rather than by trial and error.

http://reefcentral.com/index.php/head-loss-calculator
http://reefcentral.com/index.php/dra...flow-size-calc

The overflow size calculator recommends a 2-1/4" hole for 3000gph.

My own tank runs a Dart from which I get about 2300gph after head loss. My overflow is 2" but I have it dialled back slightly so that it sucks less air and makes less noise. I used to have a 1-1/2" bulkhead and when I did I had to dial back the pump because the drain couldn't keep up.

I have used those calculators in the past but my pump isn't listed so it becomes an slightly educated guess at best. I have the ball valves installed so I can dial them back which I forsee having to do.

Are you running the drain at full syphon (with a gate valve)? A 1" drain at full syphon adapted to 1 1/4" pvc should handle upwards of 2000gph.

I can't see the 1.5" having any trouble if you go full syphon.

This is one calculator I've used in the past and it seems to be really close:
http://beananimal.com/articles/hydra...-aquarist.aspx

According to it a 1 1/2" full siphon (with a submerged discharge) at 4' of head can take over 5000 gph.

Should be fine at full syphon, but it may be alot of flow through your sump which may reduce the effectiveness of your water treatment depending of your sump design of course.:wink: