Crown-Vented Laundry Drain Trap?

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Smooky

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Technically you are correct, a vent should not be installed within two pipe diameters of the trap weir but I doubt that is where the odor is coming from. Have you considered any other possible sources? Where does that dryer vent go? Does it vent out near a sewer vent? Often odor enters the living space where it is supposed to vent out. Also when the dryer is running, it is blowing a lot of air out and pulling air from wherever it can get it. When the sheetrock was put up a screw or whatever could have gone through a pipe. Are there other plumbing fixtures in that area that we don't see? You could stir up a lot of trouble but I don't think the juice is worth the squeeze. Even if you do lengthen the trap arm, I'm not convinced that will solve your odor problem.
 

Reach4

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Simply because it doesn't have a minimum of two pipe diameters as required by code. There is a reason it is required.
Yep, it does look short.
img_4.PNG

The trap arm being too short will not cause bad draining. It just helps keep the trap from siphoning.
 
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hj

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The "2 pipe diameters" is a technical requirement, NOT a "practical" one. It has NOTHING to do with your problem and if you think you do NOT have "P", trap what would you call that thing at the bottom of the standpipe riser?
 
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Kreemoweet

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Plumbers put in those traps with technically-too-short arms because contractors and carpenters refuse
to install special framing to accommodate the plumbing code requirements. The photos in this thread
show that plainly: there is no other way to install the trap without modifying the framing. Were a plumber
to tell a contractor he can't install the standpipe drain until the framing is changed, he would be regarded
as a crazy man/woman and likely be fired.

Also, in reality, it doesn't matter a bit. Those short-arm traps all work just fine. I've personally installed, and
had accepted by inspectors dozens of 'em. There's probably millions installed, all doing their job just fine.

That's the reality of it. I guess some folks have a hard time with reality.
 

Kreemoweet

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Well, belay my last! I got curious as to how, EXACTLY, that 2x pipe diam. is supposed to be measured, and looked
around a little. I found an illustration from the Illinois plumbing code, showing that the measurement is to be made from
the trap weir to the centerline of the vent. I then looked at the dimensioned drawings in the plastic pipe fitting catalog
from Charlotte Pipe & Foundry Co., and discovered that using a 2" santee in direct contact with whatever hubbed 2" trap fitting
upstream would result in said measurment being exactly 4". So, all the questioned trap installations talked about here
would be code-compliant. At least in Illinois. Good enuff for me!
 

Cool Blue Harley

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Unbelievable. Not an S trap. Simply a p-trap with an offset in the standpipe above it. If the offset was higher, just below the box, nobody would question it. Offsets look funny when they are down low. Hundreds of clothes washers are plumbed exactly like this. Yes, the distance between the trap and vent on a two inch pipe should be a minimum of two inches. That is very close. Will work just fine. NOT AN S TRAP.
 

Cool Blue Harley

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Research discovered that by placing the vent to close to the weir of the trap it was subject to clogging. When the fixture discharges, there is an upward verticvle momentum of flow on the outlet side of the trap which would enter the vent if installed on the crown of the trap to eventually foul and clog. Also the vent at the crown of the trap or close to the crown is covered by the initial full flow into the trap arm and is useless to prohibit siphonage. Therefore there is a minimum trap arm length requirement. That being said, that is not an S trap, it is an offset in a standpipe, and it will work just fine.
 
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