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Replacing a Main Line

Discussion in 'Irrigation' started by regularguy, May 28, 2011.

  1. I'm no expert on 4" pvc installation. Repaired it many times though. Whatever super expensive is repairing 4"pvc is a PIB. I'd follow Sprinkus advice myself.
  2. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,686

    gasketed mains have some wiggle room to expand and contract
  3. Sprinkus

    Sprinkus LawnSite Silver Member
    Posts: 2,108

    3" class 200 pipe will safely do around 120 gpm.
    3" sch 40 will do around 110 gpm.
  4. Waterit

    Waterit LawnSite Silver Member
    Posts: 2,906

    There are 2 Sch. 40's - one is for sewer, usually is also marked "cellular core".
    We somehow wound up with a piece on this on a truck, and when it was used to repair a broken main off a 7HP submersible... tech got to do the same repair twice.

    That cellular core stuff will work fine as a sleeve, tho.
  5. Waterit

    Waterit LawnSite Silver Member
    Posts: 2,906

    Yup, no need to go to 4" or use gasketed. And if the main is looped you could even argue for shrinking it to 2-1/2".
  6. NC_Irrigator

    NC_Irrigator LawnSite Bronze Member
    from NC
    Posts: 1,415

    You need to go with a gasketed pipe for that size and flow, and yes if you are looping it, you can def. downsize it. Pull out a flow chart and check your flows.
  7. regularguy

    regularguy LawnSite Member
    Posts: 152

    Thanks everyone for the suggestions.

    I guess my next question is if I install a 3 inch pvc main line and only push 30 GPM through it in the short term the water velocity will be very low, will low water velocity be an issue?
  8. hoskm01

    hoskm01 LawnSite Fanatic
    Posts: 5,690

    slow supply (flow) isn't a concern as long as your pressure is sufficient for proper operation of your systems components. Dont worry about maximizing the potential of the pipe.
  9. Mike Leary

    Mike Leary LawnSite Fanatic
    Posts: 21,976

    Well said. Anyone who thinks they can even get close to the "five foot a second rule", especially on piping systems over 1 1/2" is not only nuts, but might as well be either a REP or sell shoes. In other words, I'd be designing a system with a 3" main to a max flow of around 60 gpm, my friction loss would be almost zilch and I'd be way under the velocity rule.
  10. txgrassguy

    txgrassguy LawnSite Gold Member
    Posts: 3,083

    I came into this late and didn't read all of the posts . . .

    When joining 4" pipe you must bevel and clean the joints thoroughly prior to application of the solvent weld.
    Use 721 or higher temperature solvent weld.
    Have at least a ten pound mallet available with a 1" thick piece of pressure treated wood as a striking plate. There is no way you will be able to join the pipe into the socket by hand so use the strike plate and mallet to "tap" the pieces together.
    You'll hear a completely different sound once the pipe bottoms out in the socket.

    Also, be sure to immediately clean all solvent weld that may have squeezed out of the socket. I use a water soaked mechanics rag - in fact I keep a small pail available so after each joint the rag is immersed in the pail. Helps to keep the rag pliable as well as removing the inevitable soil particles that collect on the rag so each clean up is done with a relatively clean rag.

    All direction changes MUST be thrust blocked, for this I have a gas powered chop saw and a supply of narrow blocks. I cut the block to fit at least six inches past the side of each joint and use a piece of pressure treated wood as a buffer to prevent vibration related leaks from developing.

    Working with larger pipe isn't difficult - you just need to be set up properly.

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