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I installed a pex water line to an outbuilding several years ago, about 150' long, buried in 18" trench. The line was disconnected for over 3 years and I recently reconnected it and no water is reaching the outbuilding. I have removed all fittings on the far end and have open pipe, and I can hear the line pressurize when I open a valve on the supply side but there is no indication of flow.

I added a tee for testing and the buried line holds pressure when isolated for hours, so it is not leaking underground. There are no turns or bends where a kink could form. The only cause I can think of is that the line collapsed. The line is buried with an electric conduit and it would be a major effort to hand dig the line again.

Will leaving the line pressurized reverse the collapse? Is there anything I can do to aid the process?

UPDATE to questions in comments: The line is 1/2" PEX B, typical residential line. There has been a little traffic over the area where the line is buried, with a small tractor and pickup truck driven over the area perhaps 20 times. When disconnected, one end of the line had a hose bibb installed and the other was covered with tape, not airtight.

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    What's the temperature? In many areas of the Northern Hemisphere an 18 inch buried pipe in Mid February is probably plugged with frozen water. Rig up something so you can increase pressure on it to the maximum the pipe is rated for (from the house end) and leave the far end open.
    – Ecnerwal
    Feb 20 at 17:45
  • It's in Texas and air temps are 70s during the day and 40s at night, definitely no frozen ground.
    – user15741
    Feb 20 at 17:56
  • Did any cars/trucks/tractors drive over the line? I was hoping for the frozen reason, since it would take some work to collapse pex.
    – crip659
    Feb 20 at 18:13
  • Collapsing PEX is pretty difficult. Are there really no signs of physical damage to the path?
    – KMJ
    Feb 20 at 19:00
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    When it was disconnected were the ends sealed? What diameter is it? Feb 20 at 21:24

2 Answers 2

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If the PEX is or can be stripped down to the point where there are no tight bends and no fittings then you can mechanically test for an obstruction. A electrician's fish tape will fit inside the tube. If you can test from both ends then even a 75 or 100 foot tape will be long enough feed through the tube until it encounters the obstruction, but if you prefer to see the tape go through the full length of the tube (or can't test from both ends) 200 foot tapes are also available. Alternatives like a steel fence wire could be used instead. Copper wire, especially in the smaller gauges or in cable form, is likely to be too soft and won't push in more than a few tens of feet (but, if the trouble is near, that could be enough).

If you know the pipe path with high confidence you can measure off the pipe-distance to the obstruction as measured by the fish tape and have a reasonably good estimate of where the problem lies.

That said, I think a forgotten valve is more likely than a 100% sealed-off crush failure. If the pipe truly is crushed then whatever object has pinched it will also be holding the pipe fast such that using the old pipe to pull a new one is highly unlikely to succeed.

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  • It did turn out to be a valve. 100' fish tape is expensive locally so I was planning to order one from Amazon and tried fishing with a piece of wire. It was pretty obvious that it was not a crushed line because the wire hit something firm instead of slowly getting harder to push. A quick dig found it. At some point I must have installed a ball valve about 10 ft from the far end of the line. I must have needed a splice and added the valve and forgotten about it. With the valve open the line works great.
    – user15741
    Feb 23 at 18:49
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You'd have to pressurize the line to much beyond what the water will provide in order to expand the soil around the line. You'd need to plug one end and apply an air source to the other.

There's a good chance you'll burst it before you actually resolve the issue. Most pex is rated to something under 200 PSI.

One idea might be to pull a new line using the old one. If you can create a secure splice that's not significantly larger than the pipe you might get away with tugging it with a vehicle. #redneckplumbing

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    If I remember my university days correctly, when pressurizing things to their failure point, you should use incompressible fluid, over compressible gases. Though with the volume involved with a pipe, its probably not that big a deal.
    – Forward Ed
    Feb 21 at 10:31
  • Good warning. The unstated reason is the potential for violent explosion. I'm not sure how one would apply that much water pressure, though. Many of us have air compressors on hand.
    – isherwood
    Feb 21 at 13:42
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    I'd think that under 18" of cover, an exploding PEX line wouldn't throw dirt to terribly far. If the OP were to do this, though, I REALLY hope he has someone running video, just in case. :D :ROFL:
    – FreeMan
    Feb 21 at 16:12
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    @isherwood - you first fill the pipe with water, then use your air compressor to add the oomph. The water doesn't really compress, so the stored energy is all in the air volume (small). I've done that to test volumes to 600psi or more for non Home Improvement things.
    – Jon Custer
    Feb 21 at 18:52
  • That's what I figured, but you still have air available to blow out a rupture. It's not like the water prevents the air from moving. It'll explode at whatever rate the compressor tank supplies.
    – isherwood
    Feb 21 at 19:06

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