# Trench drains



## luv2plum (May 16, 2012)

Hi guys,
Might be a dumb question, I just haven't run into this before. How would you size a trench drain? It will be draining to an oil interceptor (auto shop with wash bays) but, do they get trapped and vented individually, and if so, what do you figure for hydraulic load? Could you trap a bunch together if they conform to the requirements for gang trapping? This would be in reference to the Ontario Building Code. I haven't been able to find any info on this....help!


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## Titan Plumbing (Oct 8, 2009)

Gang trapping just sounds dirty...


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## UA22PLumber (Sep 17, 2012)

They're sized based on area and expected water flow...if it's 2 or 3 bays with wash hoses,do a quick calculation to get your GPMs out of a hose at local pressure X # of hoses to get a max gpm rate....4" @1/8" pitch can handle 180gpm.....but I think you'll find if you do those calculations,you won't need much in linear feet of drain,the over-riding factor is area the owner wants covered...imagine hoseing off the floor....you don't want to have to push water too far,so you'd put a drain the width of a bay ,so water would only have to be pushed in one direction ..otherwise you might as well just put in floor drains,which would be alot cheaper...If this is 10-20 bays with gpm's in the hundreds....I'd get an engineer to double checks the calcs.

As far as individually trapping them....here,we wouldn't.They'd all have to be piped to an oil interceptor before going to sanitary.Things may be differant on your side of the lake.


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## Kleinfelterj (Jan 23, 2012)

I have never trapped a trench drain that was going into an oil separator. The separator gets vented. But basically that oil separator is like a big trap. You won't get sewer gas out of any fixture on the upstream side of an oil separator.


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