Sewer backflow preventer

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by jhoybs, Mar 1, 2012.

  1. jhoybs

    jhoybs New Member

    Messages:
    13
    Location:
    Milwaukee, WI
    I live in a 1500sq ft ranch with a full basement. Our subdivision has a high water table and there is a history of sewer backups. Our house currently has all the sewer drains in the basement draining into a sewage ejector pit whose output pipe goes up to the ceiling (of basement) and then back down into the city sewer pipes. I'm assuming that this system would keep sewage backup out of the basement until it gets up to the ceiling (top of pipe). This system seems to work - our neighborhood had sewer backup last August and we were one of the few houses without basement sewage. We've never had a sewer backup, but we've only been in the house about 2 years.

    The city has offered to install backflow preventers in all houses in the neighborhood. I need some opinions if I should allow them to install one. My thinking is that 1) I have a solution that seems to work and 2) backflow preventers have to have some downsides (maintenance, sticking, installation mess, etc.). I also have to factor into the decision that everybody in the neighborhood may have a preventer and how that would affect the drainage/backup situation.

    Any opinions would be much appreciated!
  2. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    If everyone else on the street installs backwater valves and you dont.....and theres are working. Guess what? Your going to be the "relief". You should have a check valve in the pump line that would protect you from the city sewer. If your tank is liquid tight it should protect the basement from your ejector tank overflowing.

    The proper way for the city to handle the problem would be for them to install their own relief tank with a pump and alarm to alert them of their problem.

    We do not install backwater valves in a gravity sewer.......we install a "relief" drain that consists of a pipe extended to ground level with a trap turned upside down. Any sewer overflow from the city would overflow in the yard. This is typically done for any house thats subject to a possible overflow.

    With forced main sewers there are two check valves in place and the ejector cannot be installed indoors and it must be "yard" vented witha trap upside down. If both checks fail this prevents the house from being literally filled with sewage.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,051
    Location:
    New England
    Humm, not sure which is worse, contaminating all of the soil which might be hard to scrape off along with all of the landscaping, or pumping out the basement, whose hard surfaces probably could be sanitized. Neither choice seems ideal! Glad I've never lived in a place where that was a regular event. For our sewers to back up from an overflowing main, would be almost impossible as we're about 40' above the road where the sewer line runs, and near a high point for the roadway as well.
  4. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,248
    Location:
    Land of Cheese
    Milwaukee has a combined stormwater/sanitary sewer system, which can cause sewer backups to any low-laying areas when there is a large amount of rainfall.

    Let them put in the backwater valve. It's another tool in your toolbox.
  5. jhoybs

    jhoybs New Member

    Messages:
    13
    Location:
    Milwaukee, WI
    We actually live in a subdivision (suburb of Milwaukee) whose sewer flows into a million gallon underground tank and then the sewage is pumped to Milwaukee to be processed. Since the pumping station has no battery backup, there is a chance of sewer backup when power is lost. The city is evaluating everybody in our subdivision for damaged sewer laterals to try to keep ground water out of the sewer.

    I certainly understand the argument that if everybody in the neighborhood gets a valve, it would change the dynamics, but I thought that our basement sewage ejector would still save us. I'm just concerned since 1) the city is funding the valve so we have no idea the quality of the device and 2) the fact that if the device gets stuck closed, we'd get backup on the first floor.
  6. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,248
    Location:
    Land of Cheese
    Everyone else's basements will become an additional part of the holding tank then.

    It's one of those "damned if you do, damned if you don't" scenarios.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,679
    Location:
    Cave Creek, Arizona
    YOu appear to have what is called an "overhead sewer". Unless your "ceiling" is lower than the manholes in the street the water will NEVER get that high. WE installed that type of sewer to eliminate backwater valves. Baackflow valves often create more problems than they solve. I frequently have to REMOVE the backflow devices because they are causing the stoppage in the sewer. I would so nothing, unless there is some situation peculiar to your house that we have not been told about.

    As far as your neighbors are concerned, since the valves seldom function as advertised, especially after a couple of years, they will still flood and you never will.
    Last edited: Mar 3, 2012
  8. jhoybs

    jhoybs New Member

    Messages:
    13
    Location:
    Milwaukee, WI
    hj,

    That was my thinking when I first posted. Our neighborhood did have a sewer backup in summer 2010 and our "overhead sewer" did save us. I would guess that 75% of the neighborhood had ruined items out for garbage pickup; this incident is what prompted the city to investigate. Although offering free backwater valves to the neighborhood does change the sewer dynamic, I'm really nervous about the valve. I would think that there would be too much of a chance that it would stick closed at some point and sewer would back up to the first floor.

    I'll try to post a picture of our "overhead sewer" for people to verify exactly what it is. Two pipes come out of the sealed lid (which looks identical to a sump basin). The first (output) pipe goes into a check valve and up to within 2 feet of the ceiling and then back down into the sewer line. The second (input) pipe goes to both the utility sink and what appears to be the vent stack.

    Originally, I had thought that we've be safe as long as the sewage doesn't make it to the top of the output pipe, but now that I think about it, the vent is what we have to worry about (check valve would protect the output pipe). The vent connection is not as high as the output pipe loop (probably 7 feet off the floor). Maybe I need to break into it and add a higher loop - I want to make sure that this vent loop is above the street.
  9. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,679
    Location:
    Cave Creek, Arizona
    The vent SHOULD NOT be connected to the sewer line in the first place, so if it were installed correctly, there would be no way for water to flow into it. Backflow devices can, and do, cause stoppages, and after a few years they also do NOT prevent backup flooding. You are worrying needlessly. LEAVE YOUR SEWER ALONE, it is fine just the way it is.
  10. jhoybs

    jhoybs New Member

    Messages:
    13
    Location:
    Milwaukee, WI
    Here is a picture of our current overhead sewer:

    DSC09195 (Large).jpg
  11. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,679
    Location:
    Cave Creek, Arizona
    Your photo does not show everything, but I assume that your main line is going into the floor, even though the basement plumbing is not connected to it. This would create the equivalent of an "overhead sewer" even though it does not go out through the side wall of the basement.
  12. jhoybs

    jhoybs New Member

    Messages:
    13
    Location:
    Milwaukee, WI
    hj,

    Both sewer pipes with the cleanouts go into the floor. The large pipe (left) services 2 toilets, 2 sinks, a tub and (I believe) it continues up and out the roof (we only have 1 vent - this appears to be it). It isn't directly connected to the "overhead sewer" in the picture. The smaller pipe with the cleanout (SC) has 2 connections to the "overhead sewer":

    Left basin pipe (input) tees off to sink drain and continues up and is connected to the "SC" pipe near the ceiling. The right basin pipe goes thru the check valve, up to the ceiling and then back down and is connected to the "SC" pipe near the floor (you can almost see the connection behind the broom).

    I understand that the right basin pipe is the output, but shouldn't it just connect to the sewer at a high point? It really doesn't need to go thru this big loop.

    What really throws me is the "SC" pipe - it is acting like both a sewer drain and a vent which would be fine (I think) if this system wasn't intended to protect against backups. Shouldn't the vent on this thing go directly outside and not be connected to the sewer? With this system as it is now, if sewage would back up to vent connection (right below the ceiling), wouldn't it start backing up into our basin?

    FYI - For what it is worth, the "SC" pipe comes out of the floor, goes up and connects to the "overhead sewer", tees off and continues up thru the floor (I assume that it is connected to the main vent stack in the wall - all drains accounted for on the first floor), then it runs horizontal for 20 feet and goes back down into the floor.

    By the way, I REALLY appreciate your help!
    Last edited: Mar 7, 2012
  13. jhoybs

    jhoybs New Member

    Messages:
    13
    Location:
    Milwaukee, WI
    I read this last post and you'd have to diagram it to follow it - so I did. I apologize to everyone whose heads blew up!

    Basement.jpg

    As I asked previously, why did the designer of this system connect the purple input pipe to the sewer? Wouldn't the best bet be to vent this directly outside? If it was vented outside directly, the only way sewer would backup into the basement is if the check valve failed and the sewage was almost up to the ceiling.
    Last edited: Mar 7, 2012
  14. coolcitybbq

    coolcitybbq New Member

    Messages:
    7
    Location:
    WI
    I don't think you have a sewage ejector pit. Rather it looks like a past owner created a series of standpipes. In the 6/08 and 7/10 storms your neighbor's basements served as the reliefs. I think your "sump" pit has two pumps in it that are ejecting into the storm sewer system, only exagerrating MMSD problems, instead of expelling on to the front lawn. I'd go with the city back flow valve, if you have the option install a ball valve in your basement floor that would allow you to manually shut off the flow in the event the backflow preventer fails.
  15. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,679
    Location:
    Cave Creek, Arizona
    The high loop is because the installer did not trust his check valve. Unless your basement is entirely below ground the sewer would NEVER backup that high. It would be flowing out on the ground or out of a manhole long before that.
  16. jhoybs

    jhoybs New Member

    Messages:
    13
    Location:
    Milwaukee, WI
    If you are implying that I'm dumping drain tile water into the sewer - you are incorrect. I have 3 basins in my basement with 4 pumps:

    1) Original sump pit: fed by drain tiles, pumped thru pipe in back yard - this pump has been unplugged since I moved in since it creates a swimming pool in the back yard
    2) "After-market" sump pit: fed by french drain system installed around basement walls from inside, pumped out to "storm" culvert in front yard, contains both a main pump and battery backup pump
    3) The system I describe in this thread which pumps grey water from the basement (sink & floor drain) into a pipe for ejection into the city sewer - it only contains 1 pump because I just had to replace it

    The system I'm talking about in this thread (#3) has a sole purpose of isolating the basement drains (source of sewer backup) from the main sewer lines to offer some protection against sewer backup.
  17. jhoybs

    jhoybs New Member

    Messages:
    13
    Location:
    Milwaukee, WI
    It is surprising how polarized the opinions given in this thread are. I guess backwater preventers are a touchy subject.

    hj - We have a pretty deep basement since our house uses open-web trusses for floor joists. The "failure point" in the above diagram is 7ft above the basement floor and 20" below the subfloor. I know that our house is above street level, but I can't exactly tell how far (2-3ft?). In summer 2010, the street in front of the house flooded over and the water was halfway up our front yard (I have a picture in one of my other threads). One of these floods resulted in the sewer backup that I described earlier. I'm thinking that water halfway up the yard is coming pretty close to that 7ft mark on this overhead sewer.

    Still not sure what to do...
  18. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,679
    Location:
    Cave Creek, Arizona
    Well, you could put a valve in the "vent line", but IF the pump has enough capacity, it might pump out any overflow water as fast as it comes in. But, also, if that were to occur, your neighbors will probably be up their eyeballs in water, even if they do have BWVs installed.
  19. jhoybs

    jhoybs New Member

    Messages:
    13
    Location:
    Milwaukee, WI
    Well, after thinking about this for a few weeks and talking to some plumbers, I have more information to share (for those of you who may be following this thread with similar problems).

    Our overhead sewer was installed after the house was built. To clarify, the city sewer line comes in under the basement floor and 4 pipes come up to service the house. The designer of the overhead system must have capped off all the sewer lines that drained the basement fixtures and plumbed them into an ejector pit.

    I think the reason that designer of our system didn't vent the ejector basin (purple pipe - see diagram in thread) directly to the roof was that they believed that sewer backup into the basement was preferable to backup on the first floor (if the sewage ever got that high - the "failure" point in my diagram is 7ft above the basement floor).

    The $64,000 question is: If the sewer backs up in the future, will the level get as high as 7ft above the basement floor? The city engineer told me that there is a bleed-off point around 3ft lower than this point where the holding tank(s) would overflow, but this tank is a mile away from us. Couldn't inflow pressure cause the sewer to surge in our neighborhood and go past this level 7ft mark?

    Half of the plumbers that I talked to had no faith in sewer backwater valves and the other half stated that they did believe in them as long as they have been maintained. Most of them agreed that these valves comprised the current sewer system and made it more likely to clog.
  20. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    Have a 4" pipe ran near the ceiling of the basement to the outside and turn it up and slap a 4" J-bend on it,upside down. This way it would overflow outside instead of the main level of the house. The sewage pump has a check valve.

    You might would be ok with that set up. I'd rather have sewage flowing on the lawn than in my house. Especially if its not even my sewage.
Similar Threads: Sewer backflow
Forum Title Date
Plumbing Forum, Professional & DIY Advice, Tips & Sewer transition, backflow & cleanout May 20, 2005
Plumbing Forum, Professional & DIY Advice, Tips & Help with Sewer gas in Laudry Room?! Wednesday at 2:18 PM
Plumbing Forum, Professional & DIY Advice, Tips & Dropped a 3" PVC flat clean out cover into a 4" sanitary sewer clean out... help... Sep 8, 2014
Plumbing Forum, Professional & DIY Advice, Tips & Connecting Sch 40 PCV to outside SDR-35 sewer line Aug 16, 2014
Plumbing Forum, Professional & DIY Advice, Tips & Trenchless Sewer Line Limitations? Aug 13, 2014

Share This Page