What Size Should My Overflow Plumbing Be?

[Palster]

I am currently building a sump for my 135 FOWLR and I got to thinking about the size of the plumbing I will need for the overflow drains from the tank. I was wondering what size of PVC pipe and bulkheads to use (I haven't got the tank drilled yet). The return pump will be a Mag 12 with 1" pipe returning to the tank and according to Reef Central's Head Loss Calculator by the time I take into account all the plumbing and head loss I can expect some where in the range of 850 GPH. I was thinking I should plan my plumbing to handle up to 1000 GPH. My question is with a design flow of 1000 GPH should I be looking at using two 1" drain lines and bulkheads or should I make these drain lines and bulkheads 1 1/2" or possibly a single 1 1/2" drain? I was under the impression that 1" PVC will handle approx. 600 GPH and 1 1/2" PVC will handle approx. 1300 GPH. I was just curious as to what size the plumbing is on a typical 135 gallon tank? My current 90 gallon has a single overflow with 1 1/2" plumbing draining into the sump (it was plumbed this way when I bought it).

[untamed]

My advice is to go larger than you think you need to. (2x1.5") There is no harm in making the drain too large, but problems if you make it too small.

Further, by making two of such drains you can run the "silent siphon", or "Herbie" method. Use a gate valve to cut back the flow on one of the overflows until that overflow is max'd. At this point, it will run like a siphon and be completely silent.

The second drain has a vertical standpipe and durso. This drain is only used if the first drain becomes plugged. It's an emergency backup only.

For this to work, both drains must be in the same overflow box.

The exact flow potential of a drain is a complex thing to estimate. Every situation is different.

[Palster]

Thanks for the sound advice Untamed. I am somewhat familiar with the "Herbie" method and it is one of the things I have considered. I was thinking that I probably should go with 1 1/2" plumbing but I just needed someone to confirm this. I do not get the opportunity to see a lot of other tanks and what other people are doing here in Kelowna so I rely on this site and the Internet in general for advice.

[mark]

Have 2-2" drains on my 145g running ~1000gph, pretty quiet with Durso's.