Dewatering Conduit

[TwoBlocked]

Got a small job coming up. Part of it is to "dewater" some underground 2" conduit that got flooded. Nothing is in them, just for future use. No caps had been installed on the stub ups, so the flood waters was free to enter, and they are full.

Haven't done this before. Figure to start with blowing them out with a shop vac. Once most of the water is out, keep blowing into one end while holding a hand over the other to build up pressure and then release it to "burp" more water out.

Here's my question: Should I stop after burping, or should I try to pull some kind of piston through to get all the water out? I'm concerned with getting it stuck if there is a lot of mud, or if the conduit broken under ground. I'm sure some of you fine folks have good advice for me.

 

[Seven-Delta-FortyOne]

I’ve always sucked with the shop vac, not blowed. Seemed to work better, but it’s going to depend on how long the conduit is.

If it had debris in it, I’d pull a mandrel through it then a foam block or chunk of paper. Assuming you can get a line through it.

 

[electrofelon]

Most conduits fill with water, so getting the water out just for the sake of getting the water out is pointless as it's just going to fill up again. Advise the client to not worry about it.

 

[Hv&Lv]

I haven't ever seen one of our conduits that were dry. At best they had condensate on the inside surfaces and the wire

 

[winnie]

Most conduits fill with water, so getting the water out just for the sake of getting the water out is pointless as it's just going to fill up again. Advise the client to not worry about it.

Agree on not worrying about water. But IMHO worth getting mud out before it dries. Then install caps.

 

[brycenesbitt]

should I try to pull some kind of piston through to get all the water out? I'm concerned with getting it stuck if there is a lot of mud, or if the conduit broken under ground. I'm sure some of you fine folks have good advice for me.

The traditional "piston" is a plastic bag. You put the shop vac on vacuum, tie a plastic bag to a rope, suck that through. Now you can use the rope to pull through a pig of an appropriate size. Some sort of brush ought to do.
The water is not a big deal, the potential mud is better to get out while it's mucky.
..
If the conduit is broken underground, better for the client to know now. YMMV depending on length, number of bends, etc.

 

[tom baker]

On long runs I have used vac on blow one end and vacuumed the other. The greenlee line vacuum is the best if you can use one

Greenlee makes foam plugs in conduit sizes, they have plastic ends that are a bit smaller than ID of conduit.

After you get the water out blow thru a foam plug one size smaller to make sure the ug is not full of mud.
Then the correct size will clean it out.

Blow in a pull string and cap each end

 

[ActionDave]

Leaf blower is better for blowing them out than a backwards shop vac, then suck a mouse back through.

 

[Birken Vogt]

I once had a conduit full of water that on a whim I took a SCBA bottle to and just gave it a blast with 2000 psi air straight from the valve.

Perhaps a big compressor like what is used for a jackhammer would do the same, or rent a SCUBA tank for a day, or a nitrogen bottle or CO2 bottle.

Better beware of shrapnel if the far end is not open.

It seems to me getting the water to all move in the same direction all at once with a big blast of air is more desirable than burbling through it would be like a shop vac from either end.

 

[TwoBlocked]

Most conduits fill with water, so getting the water out just for the sake of getting the water out is pointless as it's just going to fill up again. Advise the client to not worry about it.

Well, gotta do something. They are so full the water from flooding it is above the frostline. It will freeze and bust.

 

[TwoBlocked]

...

It seems to me getting the water to all move in the same direction all at once with a big blast of air is more desirable than burbling through it would be like a shop vac from either end.

That is my idea after the first blow. Cap the far end off with a hand, let the pressure build, and then release it (and duck!). Saw some guys
eventually get a plastic bag mouse through a conduit with water in it that way.

 

[TwoBlocked]

...
If the conduit is broken underground, better for the client to know now. YMMV depending on length, number of bends, etc.

You got a point there. If I can't get a piston through due to a break in the conduit, They won't have much luck when they want to use it!

 

[Hv&Lv]

Perhaps a big compressor like what is used for a jackhammer would do the same, or rent a SCUBA tank for a day, or a nitrogen bottle or CO2 bottle.

Better beware of shrapnel if the far end is not open.

That's what we used. Still do. Our runs can be 1000' 3" or 4" depending on what size MV cable we are installing.
There is an attachment for the air compressor that seals to the pipe. Run a string through the attachment and tie off to a foam rat. The other end will shoot a column of water that's is impressive to watch. We have shot water to the top of the pole with the compressor.

 

[MyCleveland]

That's what we used. Still do. Our runs can be 1000' 3" or 4" depending on what size MV cable we are installing.
There is an attachment for the air compressor that seals to the pipe. Run a string through the attachment and tie off to a foam rat. The other end will shoot a column of water that's is impressive to watch. We have shot water to the top of the pole with the compressor.
View attachment 2573838

I would like to see that in action.
Do you have a special truck for this task…large air tanks or air comp + generator?

 

[Dsg319]

Most conduits fill with water, so getting the water out just for the sake of getting the water out is pointless as it's just going to fill up again. Advise the client to not worry about it.

I’ve always said you could hold water in conduit but you will never keep it out lol

 

[Dennis Alwon]

I installed a 2" conduit about 150' . A few months later we went back and pulled a line thru--- bone dry. It was the first time I used pvc primer and then glue.

 

[TwoBlocked]

Oh! I always use primer after sanding the conduit (but not the inside of the fitting.) But then I'm the guy that reads and follows the destructions.

 

[Hv&Lv]

I would like to see that in action.
Do you have a special truck for this task…large air tanks or air comp + generator?

It's a tow behind compressor like is used for a jackhammer/rock drill

 

[cadpoint]

We do a lot of 2" PVC underground, at 25', 50', and up to 1000', we also install other various sizes of PVC underground.
We use a trailed compressor. We'll blow the line(s) then blow a jet line then install a mule rope or hawser accordingly.
We use rats, both plastic and barrels as previously described.

Granted in most cases a barrel rat will fly through a clogged or even a non clogged conduct. By design it's meant to,
it's two plastic pieces between a piece of plastic foam.

Yes a compressor and barrel rat will not be a good determiner of a broken pipe, or if there's foreign objects in your raceway.
You'll have to get the water out and run a rag through. Once you have a string in then tie a rat (of your choice) on both ends
and pull the rat through.

A knotted rat just under pipe size, pulled through, will help you determine if there's debris a problem of a compressor blown
PVC.

To comment on burping a pipe as the OP described, to me you haven't gotten the water out.
Even under higher pressure than a shop vac. you have to let the pressure building up, and it will sputter and burp as it exists.
It will run dry under higher pressure than a shop pack, then use the lone sentence above.

 

[electrofelon]

Well, gotta do something. They are so full the water from flooding it is above the frostline. It will freeze and bust.

Yeah thats a tough one, really the only permanent fix is to dig down and drill some weep holes in it and backfill with some gravel.