Why vent washing machine?

[jamiex]

i am in a condo association for a triple decker. we have many over flows. I think that it is related to a washer in basement that is not vented combined with extremely high usage of the washer. sometimes 25 cu ft /hr for 12 hours straight. its location is very close to where the kitchen stack sewage line merges with the bathroom stack sewage line. my friend says that while the washer is not professionally vented, the drain pipe is loosely connected and therefore air is getting in. i think that he is wrong, and there is a reason why code requires proper venting for washing machines.

 

[Terry]

An open standpipe has nothing to do with venting. Venting takes place on the downhill side of the p-trap.
If you are having overflows though, it's more likely that the lines needs to be cleared. It may be time to have that line snaked.

Venting the trap on a washer prevents the trap from siphoning. It the trap becomes empty, then the sewer smells from the plumbing system will waft up into the room. Sometimes it can get pretty bad.

 

[Sponsor]

 

[jamiex]

the lines have been cleared many times. the owner of the washer has his own professional auger. the usage is really high for this washer. these over flows happen during months where there are many overnight periods of usage at 25 cu ft/hr for several straight hours. the pipe between the washer and the kitchen stack gets filled up with bathroom sewage and constantly needs to be snaked. there is no good reason for bathroom sewage to be in the pipe coming from the kitchen stack.
i know nothing about venting. but i know that the washing machine above my condo's kitchen (different washer) is not vented, and it uses the vent from my sink as sewage goes down (my sink gurgles every time it drains). as it does this it leaves some of its waste in my horizontal pipe.
i think something similar is happening in the basement. the unvented washer is seeking air from the basement kitchen near the bottom of the kitchen stack. in doing so, it carries some waste it picks up from the bathroom sewage line and that sewage is trying to get through the smaller kitchen line pipes and gets stuck.
since it is running so continuously it's sewage is bound to merge with toilet sewage where the 2 lines merge.

 

[Cacher_Chick]

Massachusetts has one of the most strict plumbing and inspection code standards in the country, so I would be really surprised if a multi-unit building was constructed without proper fixture vents. In any case, there is no way for a it to cause the problem you are describing. The waste flows downhill, regardless of the vents. If the waste cannot flow properly, the pipe is restricted and needs to be properly cleared.

Even commercial washing machines only pump out a couple of times during a cycle, so the flow is never continuous. One of the reasons a washer drain hose should never be directly connected to a drain is to prevent it from pumping water upstream into other fixture drains in the case that the drain becomes clogged.

 

[jamiex]

the building is vented properly. the sewage flows down the stacks, just fine, minus a small blip with the upstairs washer (no permit).
the washer in the basement is not vented and was not inspected by the city, i doubt it was a professional plumber who installed it. it was just placed there where there are no vents, and the drain pipe is hooked directly into the sewage line within a few feet of where the kitchen and bathroom lines meet under the ground in the middle of the basement floor. this is a coin operated washer.
sewage from the bathroom line is going back into the kitchen line (part of kitchen line that is under basement floor) and clogging it. how can this happen if the sewage is flowing in the right direction?
i very much appreciate you taking the time to answer my questions!

 

[Jadnashua]

Older WM standpipes might have been piped using 1.5" pipe...today's code requires 2". What size is the pipe? New, high capacity, especially front loaders, pump water at higher typical rates than older ones, and 2" is required, along with the stand pipe being tall enough. Excessive use of detergent can be problematic as well. The choice and volume of detergent can make a huge difference.

 

[hj]

Your diagnosis it inaccurate, which is not uncommon for a lay person not versed in plumbing. The lack of a vent usually makes it drain FASTER, not overflow. Your sink could be connected in the "suds pressure zone" which WOULD cause backflow.

 

[Jadnashua]

Are the pipes plastic or galvanized?

 

[jamiex]

Are the pipes plastic or galvanized?

it is under floor, so i can't see exactly how they have it hooked up. pipes are cast iron. a pvc pipe connects the washer and goes under floor. they must have replaced a section of the cast iron with pvc to connect the washer.

 

[Jadnashua]

CI can last eons, but things like galvanized piping definitely has a life-span when used for things like a drain...it rusts and then gets rough, then catches things, and both of those things can slow the flow down by both turbulence and narrowing of the path.

 

[Cacher_Chick]

My suggestion is to have your condo association hire a state licensed plumber to diagnose the problem and bring the current washer connections up to par.
Often, so-called handymen and other folks trying to do good cause more trouble than anything.