Repairing a 4" mainline

Discussion in 'Irrigation' started by Dirty Water, Sep 26, 2005.

  1. Dirty Water

    Dirty Water LawnSite Fanatic
    Posts: 6,799

    This one is for Jerry, Bryan and 'Boots, because I know you guys have worked with large commercial systems :)

    We maintain a several hundred acre condo "neighborhood". It has one system that covers the entire place. The majority of was installed between now and 15 years ago (We've been adding to it for each condo as they build them, 77 condo's left to do...its huge.)

    Anyways, the original installers from long ago ran 4" main down the streets about 4' down, we come off those with 3" and 2" sub mains for each individual street block.

    We had a blowout last week on one of the 15 year old mains, it managed to blow out of a 45 fitting, I dug it out today and the 4" was glued into a 45 and then reinforced on one side with concrete.

    This will be my first time working with high pressure 4" line (100 gpm, 120 psi).

    A few questions on the repair. They make a 4" slipfix, I personally think it would work fine, is there anything wrong with using one? What about a Dawn Quick Couple? Should we concrete the fitting back in like the original one was?

    Gasketed pipe fittings? The original wasn't.

    Any advice?
     
  2. JeffY

    JeffY LawnSite Senior Member
    Posts: 324

    I have repaired several 4" main lines that were used for large soccer complexes. We have used the 4" flow-span to repair the breaks that occured from the company that installed the system to use just glue and no primer. Also, while it's all dug up, it may be a good idea to install a 4" gate valve, that way if there is a break down the line from the valve, you can shut the gate valve off and isolate the break without taking the whole system down. As far as concrete the fitting, I wouldn't use that as the chemicals in the concrete can soften the PVC over time. Just take the time to prime and glue the fitting properly and it should be strong enough to sustain the pressure.
     
  3. Dirty Water

    Dirty Water LawnSite Fanatic
    Posts: 6,799

    Gate valve would be a bad idea, its a circular main. Regardless, we can isolate each couple of blocks without shutting the whole thing off. The original installer designed it well.
     
  4. you need to install a thrust block, or you will repair it again, and very soon!!!!

    last I knew, concrete was still acceptable, but been out of gc for 10 years,

    thrust blocking is need on large pipes, check with toro, rainbirf ect

    tim
     
  5. Aran

    Aran LawnSite Member
    Posts: 13

    I agree with Jeffy about the valve and the primer, but think you should explore futher the idea of replacing the concrete. A 4" pipe is capable of handling 200 +GPM. If you have a change of direction such as 45's,90's,Tee's ect. the thrust blocking you have removed would be required, especially if you use gasketed pipe. The alternative would be a metal fitting with a bolt on retaining system. I would be leary of using a slip-fix so close to a 45 especially if it was not thrust blocked. I would recommend getting more information on thrust blocking from a pipe manufacturer or supplier. You could also wrap the pipe with plastic to help protect it from the concrete.
     
  6. PurpHaze

    PurpHaze LawnSite Fanatic
    Posts: 5,496

    Burlap works well also.

    :waving:
     
  7. jerryrwm

    jerryrwm LawnSite Bronze Member
    Posts: 1,274

    Jon,

    You can cut out the offending fitting. (Man I hate 45° ells and crosses - PITA to replace) Use a new 45° ell, and two gasketed repair couplings. You can cement the ell onto two pieces of pipe about 24"-36" long. Slide the repair couplings on, drop it in the hole, tap the repair couplings in place and the line is fixed. Make sure to replace the thrust blocks on the outside of the ell to secure the movement. If you cement the fitting onto the pipe beforehand, you can lay it in the ditch, cut out enough to drop the set-up in, and when you put the repair couplings in place, you can slowly pressurize the system. Then thrust block the hell out of it.

    Here's a link to the repair coupling.

    http://www.harcofittings.com/products/irrigation/pvc-fittings.html

    They are gasketed and have no center stop so they will slide onto the pipe and then slide into place. Just make sure you mark the pipe so the coupling is centered over the cut.

    There arealso PVC Repair fittings made by Spears, LASCO, etc. You can also use Epoxy-coated fittings, ductile iron, or Mechanical joint fittings but they can be very expensive.

    As for using the Slip-Fix/Flo-Span on the line, it will work, but I have sleepless nights worrying about that sucker holding. They work, and I have used the 6" on a mainline before, but like I said, it makes me nervous.

    Don't you love it when those installers use that "clear primer" on their fittings?

    Good Luck on the repair.

    Jerry
     
  8. PurpHaze

    PurpHaze LawnSite Fanatic
    Posts: 5,496

    In reality large pipe isn't much different than small pipe other than the size of the hole required and the types of tools/parts required. However... repair it wrong and the leak is MUCH greater.

    My personal "rule of thumb":
    1. Slip Fixes for lateral non-pressure lines.
    2. PVC compression couplers for pressure lines 2" and smaller or lateral lines.
    3. Galvanized compression couplers for galvanized pipe.
    4. Dresser couplings for pressurized lines 2-1/2" and larger.

    Use a couple of Romac 501 equivalent mechanical couplers. Also called "dresser couplings" or "Bakers" by some. $40-$60 per coupler but will pay for themselves with peace of mind. They bolt on and usually there are no problems unless you're working with transite (asbestos-cement pipe) that comes with rough barrel and milled end types. Diameters on transite are sometimes hard to match up with the proper seals and follower rings. They also come as "transition couplers" where you can change from one pipe type to another where there is a difference in O.D. For example, I keep a set of transition couplers on hand at all times for one of our sites where the original main line is 4" welded well casing that occasionally rusts through and leaks. It was installed back in the 50's as it was WWII surplus.

    Slip fixes will settle and leak and really shouldn't be used on pressurized lines. Manufacturers may tell you that they work great on pressurized lines but experience tells me differently. If the soil isn't perfectly compacted around them the deflection angle will cause them to leak as the slip fix "bends" during settling.

    PVC compression couplers are hard to get tight at that size. The friction on the nut/barrel threads will actually "melt" the PVC threads and you'll be back in repairing the thing at a later time. You'll think you have them tight enough and they'll hold for awhile. You can use Teflon-type lubricant on the threads but the nuts are quite large and difficult to get even large Channel Locks onto. Forget about using standard pipe wrenches on these PVC compression couplers since the PVC might crack. I use lubricant on all PVC compression couplers even down to the ½" size.

    You might still have to pour a new "dead man" or "thrust block" (concrete) to keep the pipe from creeping out of any mechanical repair.

    Email me at purphaze@sbcglobal.net and I'll give you my cell phone number if you need more help.
     
  9. Dirty Water

    Dirty Water LawnSite Fanatic
    Posts: 6,799

    Jerry, thanks for the reply. I'll look into those Harco fittings.

    I used a 3" slipfix on a broken main on another section of the condo's and its held for almost a year now. I'm thinking that perhaps the Harco fittings, and then a bunch of concrete behind the 45'..can I incase the whole thing in concrete?
     
  10. PurpHaze

    PurpHaze LawnSite Fanatic
    Posts: 5,496

    DITTO!!!

    :cool2:
     

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