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  #1  
Old 02-10-2019, 02:51 PM
John Buchtenkirch John Buchtenkirch is offline
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Default How to avoid leaking compressor piping

For too many years I beat myself up trying different sealers & methods when installing new air pipes in my shop. It was very discouraging to have to remove 4 or 6 fresh joints just to tighten one that was hissing. Iíve actually cracked pipe fittings from running them up too hard. Finally my plumber friend moved back from Colorado and showed me how to use plumberís string or wicking. Iím not saying this is the only way to do it but Iíve had excellent results. With this method Iíve actually over tightened fittings and then had to back them off 10 or 15 degrees with still no leaking problems. It takes a little extra time but you donít have re-dos so itís actually faster.

Step #1, I lightly coat the threads with sealer. #2 & #3 I hold the plumberís string with my thumb and pull it across the threads and then start wrapping in the threads starting from the end and working towards the center of the pipe (see photos). #4 after the string is installed I cover it with sealer till I canít see it. #5 I put a little dab of sealer on the internal threads...Ö.. too much here may end up inside your pipes and cause problems down the road. So now you should be in great shape unless you get a porous Chinese pipe fitting. Iím told Ward brand fittings are still made in the USA but I canít verify that. I use the Blue Block sealer only because my friend recommends itÖÖÖ Iím sure there are other good ones. Good luck ~ John Buchtenkirch
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Old 02-10-2019, 06:05 PM
cliffrod cliffrod is offline
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What is the actual string you use, John? That looks much like like cotton tatting string, not hemp or ?? Not like the regular packing twine in my plumbing kit for old faucets. I'm finding very little info online beyond urban lore.

Edit- Looks like wicking is a better search term than string....
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Last edited by cliffrod; 02-10-2019 at 06:07 PM. Reason: See edit
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Old 02-11-2019, 06:01 AM
Jerry Jackson Jerry Jackson is offline
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Nearly 20 years ago I used black iron pipe from HD to plumb my hanger and I had a terrible problem with leaking joints. I was using the factory-made threads and many of them just would not seal no matter what compound I use. The problem was caused by the threaded portion being out-of-round. Wear marks on the male pipe thread showed maybe six or eight bright spots around the circumference that was caused by machining errors---the cross section was not a simple circle but, instead, had multiple peaks separated by flats. I believe it was caused by bad bearings in the threading machine. I never did get all of them to seal. I should have had the ends re-threaded.

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Old 02-11-2019, 09:15 AM
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idickers idickers is offline
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Thanks for the neat tip! I had such consistent bad luck with threaded pipe leaking that I used all soldered copper for my lines.
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Old 02-11-2019, 12:10 PM
John Buchtenkirch John Buchtenkirch is offline
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Quote:
Originally Posted by cliffrod View Post
What is the actual string you use, John? That looks much like like cotton tatting string, not hemp or ?? Not like the regular packing twine in my plumbing kit for old faucets. I'm finding very little info online beyond urban lore.

Edit- Looks like wicking is a better search term than string....
Itís just plumberís string or wicking. Itís available at any plumberís supply house or old school hardware stores. It shouldnít be a problem to find and itís very reasonably priced. ~ John Buchtenkirch
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Old 02-11-2019, 01:29 PM
Joe Swamp Joe Swamp is offline
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In my own limited experience, I've found that the quality of the threads makes a huge difference -- junky chinese fittings and cheap pipe from HD (made on a worn out threader) is a recipe for leaky joints.

Also, threaded joints actually have a theoretically ideal tightening spec. When I did this big threaded piping job I found this old navy piping manual that specified exactly how many turns they are supposed to be turned after hand tight -- it's more than you think. With 1" pipe it's just over 3 full turns IIRC, just a little more and you bust the fitting.

A plumber once told me that wicking is typically used on old threads being reused. It's interesting that it helped out with sealing air, usually the benefit is for sealing water as the wicking expands with moisture (similar to caulking on old wooden boat hulls).
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Old 02-14-2019, 03:03 AM
David Ward David Ward is offline
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I just recently plumbed my shop with new lines of black pipe, and about 30 joints. A pipe fitter friend from a natural gas plant gave me a tip to use regular Teflon tape, then go over it with pipe dope, anti-sieze, or similar, before assembly. Itís similar in practice to the original post. Worked great with no leaks.
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Old 02-14-2019, 04:15 AM
skintkarter skintkarter is offline
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Red Stag and hemp. Will withstand a 3rd stage nuclear strike However, understand that you can't buy Red Stag jointing paste now as it caused cancer in mice when they were fed large doses of it. They all died sadly, but they sure as hell didn't leak.

Update - just Googled it and seems it is still available, although it's probably a namby pamby version of it's former self.
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Old 02-14-2019, 04:56 PM
fabricator fabricator is offline
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Default Taper thread sealant

I use this, Loctite 577. Never had a problem, even with pretty rough threads. Left over night to fully cure, it's never let me down.
Not cheap, but good stuff never is !
https://www.henkel-adhesives.com/ee/...ctite_577.html
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Old 02-14-2019, 08:44 PM
lots2learn lots2learn is offline
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Quote:
Originally Posted by David Ward View Post
I just recently plumbed my shop with new lines of black pipe, and about 30 joints. A pipe fitter friend from a natural gas plant gave me a tip to use regular Teflon tape, then go over it with pipe dope, anti-sieze, or similar, before assembly. Itís similar in practice to the original post. Worked great with no leaks.

That probably works. In washinton state it's not legal to use the normal white teflon tape on natural gas. Need to use the yellow stuff that is more pliable.

I used all copper (type L) as thats code here for my air lines but I hate the cost. Probably 100 joints.
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