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Force Main Piping

  • 1.  Force Main Piping

    Posted 27 days ago
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    What are the pros and cons of running waste water force mains under a building slab (around 400' of pipe)?
    Are there any codes or standards to go by? 


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    Eric Smith CPD.
    Plumbing Designer
    WDG Architects Engineers
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  • 2.  RE: Force Main Piping

    Posted 27 days ago
    Eric,
    I am not aware of any codes or standards that formally prohibit it, but I do not suggest it because wastewater is trapped, could not be drained by gravity and will stay in the pipe after pump stops. Then it might freeze (if it's under unheated garage space). Solids in the wastewater will eventually settle at the bottom of the pipe and clog it, especially if pump only works occasionally. Pipe under the building will be subject to forces from building settlement. Depend on pipe material it could be subject to corrosion, especially if in ground water. Finally, if pipe leaks, it will flood under-slab with waste water.
    That all being said, if you have to run it under slab- enclose the entire length in concrete and provide frequent cleanouts thru slab deck.
    Thank you

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    Gregory Shvartsman
    President
    IGS Consulting
    Plumbing and Fire Protection Design Optimization, QC, VE.
    igsplumbingeng@gmail.com
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  • 3.  RE: Force Main Piping

    Posted 26 days ago
    Thanks!

    That's pretty much what I thinking.

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    Eric Smith CPD.
    Plumbing Designer
    WDG Architects Engineers
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  • 4.  RE: Force Main Piping

    Posted 26 days ago
    Eric;
    I certainly do not know the codes or regulations on this application. Nonetheless, I would be uneasy with this proposition and would look for any other reasonable (and maybe UNreasonable) method to avoid it. If absolutely unavoidable, then I would make it as fortified as possible; 1) Limit number of fittings and joints in piping; 2) Provide cleanouts and as necessary, air relief, but control where they occur and coordinate those access points with other trade (including HVAC for exhaust); consider containment through the length of run under building; provide minimal slope in run to allow drainage if service is required.
    That's a lot of extra work, but the potential for disaster is an important factor in your decision.
    Thanks.

    Good Luck!

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    Dennis Connelly
    Newcomb & Boyd
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  • 5.  RE: Force Main Piping

    Posted 25 days ago
    What about running the force main piping above the ceiling for about 400' ? Any special guidelines?


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    Eric Smith CPD.
    Plumbing Designer
    WDG Architects Engineers
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  • 6.  RE: Force Main Piping

    Posted 25 days ago
    the concerns are similar, but accessibility is better. Robust joint connections; think about expansion and thrust loads, maybe containment pipe.This would be the boss pipe in the ceiling; everybody else gives way.
    Neither is great because of potentially huge mess if a failure occurs, so I just make it a tough-as-nails installation and hope you're retired when it finally blows! :-/

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    Dennis Connelly
    Newcomb & Boyd
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  • 7.  RE: Force Main Piping

    Posted 26 days ago
    Could you run it all gravity to outside the building. Place the pump and basin on the plan right side outside the building then pump to the waste water treatment from there?

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    Zachary J. Nolan, E.I.T., C.P.D.
    Project Engineer
    Strickland Engineering
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  • 8.  RE: Force Main Piping

    Posted 25 days ago
    Why did you elect to pump the waste (red and blue lines) and not run by gravity.  Most plumbing drainage pipe and fittings are well suited for gravity drainage.  Cleanouts in a pressure piping system need to be valved to relieve the pressure in the system, then they can be opened for cleaning.  A deep sump and pump would be the easiest design after entering the WW Treatment Unit (dark blue square). 
    Did you evaluate using the overhead space to pump to and then use gravity piping from there?
    What is the light blue line pumping, is it sanitary waste or industrial liquid waste?  I don't agree with the long 45's in an open floor plan.  It is very difficult in the future to gauge where the pipe is located below the slab.  
    How much waste water is being generated (red and light blue lines)?  If you pump the liquid will you develop enough velocity to provide some scouring of the settled liquid/solid at each pump cycle?  How big are the pumps and sumps?
    Next topic, why is the storm drainage piping so close to the building foundation/footings?  Can an excavator get that close?  Why are you showing the storm drainage in the lower left corner running below the spread footings for the structure? 
    Too many questions for a simple answer.

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    Dave Holst
    MPLS Sr. Eng.
    David N. Holst Consulting LLC
    215-805-7002
    dave@holstonline.us
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  • 9.  RE: Force Main Piping

    Posted 7 days ago
    Eric:

    I agree with the other guys about running under or over the slab for the red line.  It looks like you are trying to get to a gravity green line on the right side.  Can't you pump up to grade and have Civil Engineer pick up the stubout on-site?  Is this an elevator sump you are pumping out?  Are the elevators traction or hydraulic?  If traction, you may have some possibilities for talking with AHJ about disposal of sump discharge.

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    John Yee
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  • 10.  RE: Force Main Piping

    Posted 7 days ago
    I have always (53 years) avoided installing pressure piping under the floor slab below grade.  There are enough problems with gravity piping (sanitary and storm) but with pressure piping (domestic and fire service), I have always minimized the below slab installation.  Over time underground piping is a mystery and without notice serious problems can show up.  

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    Dave,
    David N. Holst Consulting, LLC
    Ph: 215-805-7002