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Another pressure pipe discussion...

Discussion in 'General Industry Questions' started by digger242j, Aug 6, 2017.

  1. digger242j

    digger242j Administrator

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    ...Since there's recently been another one going on. This one's sorta the same, but different.

    We had a little job a couple of weeks ago, at one of our local municipality's sewage treatment plant. It involved repairing a small sinkhole in a paved area.

    There's a 3 inch "plant water" line, that leads from the one building to the tanks that process the raw sewage. As I understand it, water is occasionally used to wash down some of the equipment, and it doesn't need to be drinking water, so water that's already been through the treatment process is used. A pipe runs underground, and then at several points tees branch off and go up the side of the tanks. Since we have cold winters here, those lines needs to be drained in freezing weather. The drain can't just run to daylight, because the water is technically not ready to be discharged from the plant yet, so was a 3" x1" tee, with a curb stop attached, and the water was allowed to drain into the gravel bed around a larger (18" ductile iron), raw sewage pipe below.

    The sinkhole apparently happened because either somebody left the line pressurized when they opened the drain, or the pipe broke off at the tee, which allowed an excessive amount of water to run. When we dug it up, it was broken. The 3" valve that controls this setup is right in front of the tee.

    The first part of the job involved installing a new valve, inside the building, so that we could isolate the problem area from the rest of the system, which needed to remain active. That was pretty simple. The access was easy, and we cut out a section of pipe, installed two flanged ends, and slipped the new valve in between them, and bolted it all up. We opened the valve to test for leaks, and then shut it again so that we could proceed to the next part, which was digging up the problem area and figuring out a solution.

    First pic shows the site:
    SUNP0020.JPG

    On edit: ignore the time stamp on any of the pics. I took them with a digital camera, which had been sitting with the batteries removed for quite some time, and didn't realize the date needed to be reset.
     
    Last edited: Aug 6, 2017
    CM1995 likes this.
  2. digger242j

    digger242j Administrator

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    The pipe supplier came up with a nifty little fitting that should make a job like this a breeze. SUNP0024.JPG


    It telescopes in and out. You cut out the pipe where you want to connect, glue in your new tee, glue the fixed end of the coupling to the existing pipe, apply your glue to the bell of the new tee and the end of the coupling, and simply telescope it out into place.

    Pics of the coupling, in both positions: SUNP0023.JPG

    SUNP0022.JPG

    The issue that concerned me, and the reason for this thread, is what happened when we went to cut the existing pipe in order to insert the new tee.

    I got most of the way through, when the blade got bound up in the cut. Even with two of us trying to pull on the pipe this way and that, it wouldn't come free, or cut any further.

    You can see the sawzall blade, stuck, just on the right side of the old tee. actually, you can see it in the previous picture as well. SUNP0021.JPG

    At this point, I started to get the feeling that something wasn't right, and we stopped to reconsider things. Before I go any further, I'd be interested in seeing if anybody else thinks the same thing I was...
     
  3. Scrub Puller

    Scrub Puller Senior Member

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    Yair . . .

    Dunno digger but at the golf course I don't think I was ever able to cut three inch without binding. Standard procedure was to do three or four cuts close together from each side to ease the pressure and then trim the ends one the cut was completed.

    I used a coupling that could accommodate up to (Ithink) six inches between the ends of the pipe.

    Off topic . . . where the hell have the formatting options gone!!

    Cheers
     
  4. td25c

    td25c Senior Member

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    Sounds like the water pressure on the other side of the valve is causing the pipe to compress pinching the saw blade .

    Any valves further back where you could shut the water off ?
     
  5. Shimmy1

    Shimmy1 Senior Member

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    5 min. SMH.
     
  6. digger242j

    digger242j Administrator

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    That's exactly what I was thinking. And yes, the valve we'd cut in inside the building did in fact have the water shut off, but the residual pressure was still there. We hadn't relieved it by opening the valve in the picture.

    And to Scrub's point, we did make a second cut after relieving the pressure in the line, just to make it easier on ourselves. I don't know whether we could've completed the first cut or not. The cut at the other end, where the coupling was to go, went uneventfully

    So, ok, we solved that problem simply enough. The next question is, is there something else to consider before using the hardware that was supplied?
     
  7. Hobbytime

    Hobbytime Senior Member

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    I use slip couplings , they make them for pressure lines to glue, I dont like the idea of a few o rings ( in that expandable fitting)holding back the water and that it can move even after being glued...most likely the unreleased water pressure was binding the cut.. also no pictures are showing in your 2nd post, they were there when scrolling down then poof gone, this has happened in other threads...no idea why...:confused:
     
  8. td25c

    td25c Senior Member

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  9. Hobbytime

    Hobbytime Senior Member

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    ok now the pics are showing..another possible reason for the binding is the pvc pipe was cold when dug up and as the sun heats it, it expanded as your cutting and bond up the blade...
     
  10. Shimmy1

    Shimmy1 Senior Member

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    I would be leery of that telescoping coupler........seems unlikely the valve will stay on the pipe unless you block/stake/anchor the hell out of it. I like TD25's fittings.
     
  11. td25c

    td25c Senior Member

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    Funny story about water pipe & pressure .

    Father in law had me cutting down the road bank in front of his home with the Fiat - Allis HD16

    Was hogging in the slot parallel to the county road right beside the ditch .

    Was getting along great then looked back and had just exposed a 3" PVC water main in the center of the slot between the dozer tracks :eek:.
    Hopped off the machine to go inspect and by the time I got to it the pipe was starting to curl & raise up in the center .
    I stood on it & yelled at the father in law " bring a hand shovel quick fast " .

    We got dirt packed on it & walked the dozer up out real careful .

    Called the water company as we had them locate it first and everything was supposed to be cool .
    Water guy looked at it & said " TD ..............You must be livin rite not to have busted that main " .
    Scratched his head ....... Then fessed up he read the map wrong , measured off the edge of the road and should have measured off the center .:D
    We covered it all back over & finished out the slope .

    It was on a Friday evening to boot . LOL!
     
    Last edited: Aug 6, 2017
  12. Hobbytime

    Hobbytime Senior Member

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    whats the pressure running through that pipe?
     
  13. digger242j

    digger242j Administrator

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    If I recall correctly, it has 80psi in it.

    Shimmy nailed it. I was worried that once the pressure was back on, there'd be nothing to keep that coupling from telescoping back into itself, other than the megalugs on the valve. (We did have a debate too, about whether those are megalugs, or some other kind of retaining system, but there is something every 90 degrees around the glands on the valve.) The valve isn't very far at all from the coupling, and it wouldn't have to move very far at all for the pipe to come out of it.

    Here's the way the hardware laid out in the hole: SUNP0026.JPG

    Sorry I don't have a pic of the completed installation. Once we got it all hooked up I didn't have time to take any more.

    Just for reference, here's the valve: SUNP0027.JPG

    I kinda like those compression fittings TD linked to. Depending on how much room they take up, they might've been a good alternative.

    As it was, we had a long discussion with the pipe supplier, and I'm not sure he quite got the gist of the issue. At any rate, he didn't think this coupling would be a problem. (That's why I'm not sure he fully understood. And also why I asked you guys. I didn't think I'd be the only one to see a possible problem.)

    This was all taking place on a Friday afternoon, and we really wanted to get the job done and closed up and get the equipment back out of there, so getting hold of different hardware really wasn't the best solution. (Well, it might've been the best solution, but it wasn't the most desirable.)

    So, what would you have done?
     
  14. td25c

    td25c Senior Member

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    The " Red Neck " solution would be grab two 3 " PVC couplers & take out the center stop lip with a die grinder . Now ya got a slip coupler .

    Build pipe works to length & slip couple it together .

    Got to be really quick with the glue procedure , Pipe needs to be cool so glue don't set up to fast .:D
     
  15. Shimmy1

    Shimmy1 Senior Member

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    As long as the tee didn't have to be in the EXACT same spot, I would use either a gasketed or solvent-weld tee (whatever you prefer) and a gasketed repair coupling. Slip the repair coupling all the way on the pipe in the valve. Next, figure out how long of a stub to put in the tee so when the tee is installed, the stub is tight to the pipe in the valve when the tee is bottomed on other pipe. Install stub in tee, install tee on pipe. Last, slide repair coupling onto stub to complete the repair. To make sure everything stays in place, some 2' lengths of #4 rebar can be pounded in next to the pipe at the edges of the tee and the coupler, one on each side, then tie wire them together.
     
  16. DIYDAVE

    DIYDAVE Senior Member

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    TRUE redneck solution, is to order some of that tape, that the "I sawed dis boat in haff" guy sells on TV... Then he can have a new pitch line, like "Dis tape sticks to sh!t"...;)

     
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  17. Ronsii

    Ronsii Senior Member

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    Have done this many times usually with 2 inch and smaller though... helps to have two guys one to keep the coupler moving and one to douse it with glue once you over-slip it.. also I find I get more 'working time' if i glue both parts a couple times so the glue is on it for at least a minute before assembling. also I just use a good sharp pocket knife to remove the center mainly because I don't have a grinder with me in the trench ;)
     
  18. digger242j

    digger242j Administrator

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    All valid suggestions (well, except for the tape one.):p But you guys are over-thinking it. Or maybe we're just lazy...

    We just used that nifty telescoping coupling and abandoned the valve in place and buried it. Left the box out so nobody could turn it off, and backfilled. Of course, we made good and darn sure it was open before we did that, but since we'd installed the new valve inside the building the old one wasn't necessary. Now, there's never going to be any pressure differential between one end of the telescoping coupling and the other, so no danger of it allowing the valve to slip off the pipe.

    Of course, there'll be a bit more water to drain out, because now it has to drain about 50' of 3" pipe rather than 2', but that shouldn't be critical. One other change we made was to use a 1" plastic valve for the drain valve, rather than the existing brass curb stop. And we installed a meter pit over it, rather than re-using the old curb box. This was necessary because the handle on the plastic valve would never fit in a curb box, but it gives the added benefit of the plant operator being able to actually look into the pit and see if and how much water is flowing out of the drain and percolating into the gravel. That meter pit is shown laying on the dirt pile in the very first pic.

    On edit: Also, thanks, everybody, for the informed opinions. I wasn't 100% sure our worries about the thing coming apart under pressure were valid, but enough of you echoed my own thinking that it seems like we made a good call...
     
  19. Hobbytime

    Hobbytime Senior Member

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    the only issue you would have is what fittings are aloud underground to be buried by the governing body, just cause they make the part doesnt mean its legal to use...in my area there are lots of fittings and clamps not aloud to be used underground...
     
  20. oceanobob

    oceanobob Senior Member

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    Any hope to invoke a restraint clamp (split fitting)?