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Plumbing in the Home/Backflow Valve/Sewer Drainage


Wilbour wrote at 2009-07-28 15:53:25
One of the reasons for a backflow valve is to prevent water/waste from entering your basement via the floor drain. Here in Ottawa, Ontario, Canada we have just had our third flood in 15 years due to extream rainfall and our sewers could not handle the volume. The water backed up in to 400 basements. If we had efective backflow valves installed we would have dry homes

Keef wrote at 2009-09-12 16:01:03
Ok first the purpose. Say the municipal sewer backs up. that flap closes and prevents sewage from going reverse into your home. Not all states and city's mandate this in their building codes/ordinances. However some homes may not have this if it is required because they are grand-fathered in meaning it was built before the code/Ordinance was enacted therefor you aren't required to change the setup. These really are something everyone should install because who wants raw sewage overflowing into their home. In fact there are many case's of a city municipal system overflowing into homes and contaminating the homes so bad they are condemned and there is a significant financial & personal loss. The back flow prevent-er in your picture looks to be very old and i doubt it still functions correctly. The estimate the plumber gave you sounds very high and i would price shop within reason. Dont go with someone who isn't reputable DO YOUR RESEARCH. This will significantly raise the value of your home if resale is in the future. Also do some research on the municipality sewer history in your area. Often city and rural systems are 30+ Plus years old which can at anytime fail and dump sewage into your home if you have a faulty back-flow prevent-er or none at all Good luck!

crappier wrote at 2010-05-17 13:29:14
better late than never, but Tim if you don't know why a back flow preventer was installed, you shouldn't be doling out advice on these sites.

It is there to keep sewage from backing up into the house.  Waste can flow out (if it's functioning properly)  but a sewer back-up can't come back in.

Now there are issues with the way the PVC is installed AFTER the BFP, essentially rendering it useless, but other than that, they are typically a good idea to have.  It is also recommended that you check the flapper at least once per year to make sure it's not sticking or clogged which would affect the outgoing flow, as described in the original request.

Sam wrote at 2012-04-22 12:53:24
Tim, I live in Michigan around the Grand Rapids area. I had a back up and am considering a flap also. Now around here the city view is that it's an act of God. Also home owner's policy covers up to $ 5,000.00 of loss. I don't want to go thru this ever again . Need to no the pros and con's. And you said something about a force or sealed system. Thanks again. Sam

Jeremy wrote at 2012-06-11 16:35:51
These are actually called a backwater preventer, and keep the city sewer from back up into the house in the case of a major rain even, low lying house, and the city sewer is full and can't handle it. It keeps their problem from becoming your problem. I live by a lake with high ground water table had the city sewer back up quite often into my house. Installed one of these and it is no longer a problem... So long and short of it that is what they do. The previous owner probably had a few of these basement flooding events take place and said enough is enough like I did.  Ruined water heaters, washer/dryers, stuff you would store in a basement. Cost $2500 to put in and is a damn good investment.

Brad wrote at 2012-07-13 19:59:56
Hi Tim.  What this gentleman has is a Backwater Valve. This valve is to stop reverse flow of the sewer line from returning into the house. I live in Vancouve B.C. and they are common up here.The inherent flaw to them is that solids can inhibit the check valve from fully opening or closing, They take a little maintenance to keep them working right but it is well worth it if it stops the sewer from backing up into the house.I would recommend that the homeowner takes the time to regularly check out the valve and remove anything that could stop the valve from working properly. I know that for the non plumber this may seem like a very objectionable task, but it is worth it.  

Jerry Harness wrote at 2012-08-27 18:43:15
Backflow devices on sewer lines are important if you live in an area when the city sewers can backup due to large amounts of rain; in which case the city sewage actually backs up into your home. If you don't feel this is a problem in your area, you can have the device removed and replace with a simple pipe. The alternative of simply removing the flap may work, yet this would render the device useless if your city sewage does back up.

Note: These devices are usually never required by building code and usually only installed on homes that have experienced these problems in the past. Remove at your own risk as this form of flooding is not covered by flood insurance.  

JRHandyman wrote at 2012-10-28 02:31:06
There is another reason for a back flow valve in your main drain/sewer pipe.  If the drain pipe coming out of your house is lower in elevation then the manhole cover in the street where you drain pipe flows into, a back flow valve like the one in the picture is usually required.  IE, you live on the downhill end of your street or your front yard goes up hill.  The valve should be installed at the point in your house or crawl space that is closest to where the pipe leaves the house.  This is done because if for some reason, the public sewer system floods and backs up, like you may have seen somewhere, enough so that water comes up through the manhole cover, then guess what, that water is also going to rise up coming backwards into your home through the drain pipe and out into your toilets, sinks, tubs, etc.  The back flow valve is supposed to stop that from happening.  These valves do require periodic maintenance though, as the flapper can break off or get clogged.  Admittedly, flooding of this magnitude is probably rare, but, how lucky do you feel?

jrich wrote at 2012-11-26 22:29:25
Backflow preventers are used in areas that experience flooding especially during storms. When storm water over powers the sewer system sewer?waste water can back up into your house flooding the basement with waste water. If that is not a problem in your area it may be ok to remove. Check with your local DEP or what ever municipal agency to see if it is required by code.

Drew wrote at 2013-04-18 14:36:17
This answer from the "expert" is not correct and could be harmful.   A lot of homes connected to sewer have this type of backflow device. Actually code for most new homes requires a backflow if the lowest point in a homes waste pipes is below 24" of the nearest manhole outlet.  This is a very valuable device that keeps the city sewer from entering a home. If you live in an area likely to flood or in an area with a high watertable this is a necessity and possibly code.  The trick here is to keep it clean and functioning.  Clean & Clear so it doesn't get stuck closed or partially blocked.    Any reputable plumber  would know about a sewer backflow.  

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Timothy Whartenby


I can answer just about any plumbing questions



Local 690 Philadelphia.

noneI've been a foreman/Supervisor for over 5 Big Union Companies.

Master Plumber since I was 25 yrs old was Journeyman at age 16. I'm a Union Plumber Foreman since 18yrs old as my Father owned Family business. Now I work through Plumbers Union Local 690

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Youngest Journeyman in Phila, Pa. I was 16 when I passed Journeyman test

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