PVC Flow Capacity Question...

[WDLV]

I'm in the process of planning a system and was researching different aspects of flow capacity for different sizes of PVC piping. I determined that (per the RC calculator) that the max flow rate (3740+700 = 4,440 GPH) I plan to run through my overflows (2.75" required) would be within the tolerance of my two 1.5" drain pipes.

However, I just read elsewhere that the max flow rate through a 1.5" PVC pipe is 44 GPM (2640 GPH.) I know this is not accurate because the reeflo barracudas I used to use on my old CLs was about double that and ran fine for better than three years. I plan on using a Hammerhead on my CL this time around.

I guess I just sort of answered my own question but I'd still like to know; what is the max flow rate for a 1.5" PVC pipe? I want both the drain capacity and the pump capacity....

 

[WDLV]

I answered the drain flow capacity question using trial and error on the calculator...
but now I have another question:

If the max flow through a 1.5" drain is 1325 GPH, I have a problem 'cause that's only giving me a max capacity of 2650GPH and I need 4440. If I increase the size of the pipe on both sides of the bulkhead to 2" can I get a higher flow rate even with the bulkhead being 1.5"?It's OK if I have to throttle the pumps back a little but I don't want too much back pressure.

 

[BonsaiNut]

I use this chart for my planning. Hasn't let me down so far.

Low pressure drain flow capacity (gravity to low pressure) for a single 1.5" schedule 40 PVC pipe is 35 gph, or 2100 gph - with NO FITTINGS OR BENDS. Average pressure return (20-100 PSI) for 1.5" schedule 40 is 81 gph, or 4830 gph.

Personally, I'm a big fan of running oversized overflows so that you account for snails, fish, whatever decides it wants to go for a waterfall ride. I don't know what ratio you feel comfortable with, but my gut always tells me to never run a return pump at greater than 50% the capacity of my overflows. Different people have different risk profiles

Piping is one of the lowest costs of your system. Bigger is almost always going to be better - it allows for a safety margin and flexibility.

 

[WDLV]

I guess I'd better tell them to make them 2" drains.