Dewatering Conduit

[electrofelon]

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.

Yeah you certainly can keep the water out if you do a more careful job, and primer I think helps. I have always said there are times when this is important, like when you have a conduit sloping down hill and into a basement.

 

[Hv&Lv]

Yeah you certainly can keep the water out if you do a more careful job, and primer I think helps. I have always said there are times when this is important, like when you have a conduit sloping down hill and into a basement.

Both ends must be sealed to keep out condensate.
Otherwise there will be some water in a pipe glued tight

 

[Birken Vogt]

My conduits never seem to have water in them. But I live in a very dry climate.

 

[electrofelon]

Both ends must be sealed to keep out condensate.
Otherwise there will be some water in a pipe glued tight

Sure but the issue I am talking about is when a conduit slopes downhill through a wet area into a basement, and has joints that are not watertight. I have seen a continuous stream that is very hard to stop.

 

[Hv&Lv]

Sure but the issue I am talking about is when a conduit slopes downhill through a wet area into a basement, and has joints that are not watertight. I have seen a continuous stream that is very hard to stop.

Oh yes. When we leave a transformer or a vault and go downhill to a house we put everything in conduit. We have had water come into the meter bases go into the breaker panels and leaking inside the house. For those we will put a hole in the backside of the elbow where it turns up to the meter base.

 

[TwoBlocked]

Soooo, There were four 2" stub ups that are supposedly making up two underground 2" PVC conduits. One, I could see some water in. One at a time, I blew into them with a 20 gal shop vac. Could tell a large amount of air was going in from the suction on the shop vac, BUT NO AIR COMING OUT OF ANY OF THE CONDUITS!!! So I then tried suction on each of them, little or no air coming out and no suction on any of the conduits. I Did get a little water on 3 of the conduits, less than a gallon all together.

My guess is the conduits are broken underground and there are pools of water. Dry fitted caps on the conduits and marked "NFG."

I do wonder why I could blow air, but not suck...

 

[Birken Vogt]

I do wonder why I could blow air, but not suck...

Unidentified hand hole somewhere along the run causing air to go in an unknown direction?

 

[electrofelon]

can you try putting a fish tape in to confirm if its broken? I recall trying to get water out of conduits with a shop vac and not having much luck.

 

[TwoBlocked]

Unidentified hand hole somewhere along the run causing air to go in an unknown direction?

No hand holes anywhere. Checked JB / pull boxes for air blowing out - nothing.

 

[TwoBlocked]

can you try putting a fish tape in to confirm if its broken? I recall trying to get water out of conduits with a shop vac and not having much luck.

Wasn't going to risk losing a fish tape. Besides, They don't need it now, just wanted it cleared out for future use. It is designated for temporary instrumentation so they will probably go wireless if needed.

 

[retirede]

I do wonder why I could blow air, but not suck...

Hard to speculate without a P/V curve for each side of the vac.



The “NFG” markings are telling! “No F’n Good”

 

[SceneryDriver]

Got a plumber friend with a camera snake? That could tell you a lot.


SceneryDriver

 

[Strathead]

I am with the tow behind air compressor option. You don't really need the sealing rig shown but it is a nice addition. A couple rags will do the trick. Make sure to have your apprentice guard the other end. (just kidding) make sure no one is within 20 feet of the other need of the conduit.
Barring that, using a vacuum cleaner you need to "rock the boat" not plug and end and try to pop it. Rock the boat is suck, remove, suck remove, in a rhythm like 1,2,3...1,2,3... the water will start rocking back and forth.

 

[Knuckle Dragger]

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.

I know I'm late to the discussion. If it's a lot of water I would pull a mouse (some kind of piston) threw then plow or suck. The water could be too heavy blow with a shop vac ( maybe ren a large compressor).
Goodluck!

 

[JohnE]

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.

It's a tow behind compressor like is used for a jackhammer/rock drill
View attachment 2573840

I've used a compressor like this for what is described in the OP, this was going to be my suggestion, depending on conduit size.

 

[electrofelon]

Yeah I am just remembering an electrician friend of mine telling me how he had to rent one of those big boy not screwing around tow behind air compressors to blow a line through. IT was a big pipe filled with water and I guess neither the shop vac nor the homeowner harry air compressor would do the job.

 

[TwoBlocked]

Yeah I am just remembering an electrician friend of mine telling me how he had to rent one of those big boy not screwing around tow behind air compressors to blow a line through. IT was a big pipe filled with water and I guess neither the shop vac nor the homeowner harry air compressor would do the job.

Yeah, but air blew into the conduit very well without any coming out of another conduit. Then when sucking, it would be almost a vacuum, drawing only a little water.

 

[neault]

Velocity moves the water. You can plug the shop vac with your hand, and may not be able to push through. Low pressure high volume will be best. Look to the irrigation contractors that blow out the lines at the end of season.

 

[Hv&Lv]

I don't think irrigation is pushing 2,000lbs of water

 

[retirede]

I don't think irrigation is pushing 2,000lbs of water

It doesn’t matter. The amount of pressure required to expel the water is largely determined by the burial depth. For very long runs, friction will come into play once it starts moving.

If a pipe is buried 3’, applying a pressure greater than 36” WC will start pushing the water out. The higher the pressure, the faster, as long as the air source can supply the required flow.