Big EMT Fishing

the problem with blowing a walmart sack through a conduit with forced air, versus sucking the sack through the conduit with a vaccum, is that under the negative pressure of a vacuum, if tied correctly the bag will inflate. what i mean is, if you tie the sack with the correct size of potential "bag", that bag will inflate inside of the conduit under a vacuum, and seal itselt to the sides of the conduit, to run through the conduit as fast as the air will move. when blowing a line, you're using positive pressure and hoping it somehow catches the air like a parachute.
 
We always had Greenlee or Enerpac systems or Jet Line bottles and this was a non issue. If we were using set screw fittings we would tape the couplings. This could be a little problematic because we would have to remove the tape and if we were talking about 20 to 50 conduits it could be time consuming.
 
I don't know if the bag ever inflated fully when vacuuming. Didn't have a camera in the pipe. Most of our stuff was sealed up pretty well. We could suck a Walmart bag thru 1/4 mile of conduit with a decent shop vac. We tried misc bags but Walmart seemed to be the best
i've even heard of some folks using partially-inflated water balloons. i've never tried it, but sounds like it has great success.
 
We always had Greenlee or Enerpac systems or Jet Line bottles and this was a non issue. If we were using set screw fittings we would tape the couplings. This could be a little problematic because we would have to remove the tape and if we were talking about 20 to 50 conduits it could be time consuming.
maybe put a bit of clear caulk on the couplings as you are making up the run so you won't have to come back and remove anything?

compression fittings probably still cost less overall when you figure in the added time to tape/caulk plus coming back to remove tape.
 
I don't know if the bag ever inflated fully when vacuuming. Didn't have a camera in the pipe. Most of our stuff was sealed up pretty well. We could suck a Walmart bag thru 1/4 mile of conduit with a decent shop vac. We tried misc bags but Walmart seemed to be the best
I think they can fully inflate and have too much side wall pressure to pull in sometimes. I've taken these plastic shopping bags and wrapped rings of tape around them to keep full length of the bag from being able to fully inflate yet the un-taped portions will still inflate but have less total surface contact. They seem to vacuum through better than a non taped bag does. Most the pulls I done this with were underground PVC though. I also learned it generally works best to pull a string through ASAP after making up the conduit with underground runs. Get some moisture in the run because you didn't pull conductors until some time later and they don't tend to vacuum a bag through as easily as when totally dry. If you know there is moisture causing problems when you try to vacuum you may be able to just put the vacuum on the line and let it run for a while. But any significantly low spots may hold too much water and still give you troubles.

Back when I worked for someone else, they had the Greenlee blower system, that would blow out all the water pretty easily.
One time we were going to pull a fish line for a service lateral - we installed conduit, POCO provided conductors. POCO had one those insulating caps they use on transformer bushings on top of the 2 inch raceway end near top of pole. POCO guy said he could go remove that when I was getting ready to blow a mouse through the line. I put the blower on my end of pipe for a few seconds and his cap popped off and fell to the ground. I don't think a shop vac would have had enough umph to do that.
 
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maybe put a bit of clear caulk on the couplings as you are making up the run so you won't have to come back and remove anything?

compression fittings probably still cost less overall when you figure in the added time to tape/caulk plus coming back to remove tape.
Clear silicone caulk is the most common practice in my area for long runs of large EMT. Important to note that the silicone goes on the EMT before it is inserted into the coupling. I once "fished" 200' of 2.5" EMT with about 210 degrees of bend in about 5 seconds with a home depot shop vac. Obviously there's material and labor costs for the silicon, but it's almost foolproof.
 
Clear silicone caulk is the most common practice in my area for long runs of large EMT. Important to note that the silicone goes on the EMT before it is inserted into the coupling. I once "fished" 200' of 2.5" EMT with about 210 degrees of bend in about 5 seconds with a home depot shop vac. Obviously there's material and labor costs for the silicon, but it's almost foolproof.
Does the silicone caulk compromise bonding of metal parts?
 
the problem with blowing a walmart sack through a conduit with forced air, versus sucking the sack through the conduit with a vaccum, is that under the negative pressure of a vacuum, if tied correctly the bag will inflate. what i mean is, if you tie the sack with the correct size of potential "bag", that bag will inflate inside of the conduit under a vacuum, and seal itselt to the sides of the conduit, to run through the conduit as fast as the air will move. when blowing a line, you're using positive pressure and hoping it somehow catches the air like a parachute.
Just buy a couple mice instead of the bag. Use a full on compressor if you need to. The one thing with a compressor, make sure you have some friction on the string so the mouse, pulls the string or the string will bunch up and that is a real bummer.
 
Big fiberglass fish tape utility guys use on underground. On a 4’ tall reel. Usually 7/16” diameter. Won’t go through anything less than 3”.
That probably has more to do with the bend radius than the conduit size. So maybe it would work with larger radius bends?

With 450' between pull points, using larger radius elbows might make the wire pull a lot easier.
 
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