Tape vs dope

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Old 03-08-14, 03:48 PM
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Tape vs dope

I have used teflon tape for probably 35 years or more, but almost always on plastic, copper, brass, or bronze joints. And rarely with a leak. Today I spent hours assembling a complex manifold for a sprinkler system using galvanized steel pipe and fittings and bronze valves and hose bibs. I used Teflon tape, three layers, applied in the correct direction, and tightened the fittings very tight, but not so tight as to crack them. Fortunately I had the sense to pressure test it before I set it in concrete. It leaked all over the place.

Now I am going to have to take it all apart and redo it. If I use dope will I be happy, or will I just feel like a dope?

Now I know this has probably been discussed quite a bit already, so don't be mad - I have an extenuating circumstance/question that never seems to come up in the tape -vs- dope discussions.

The manifold and routing assemblage I am making is a complex entanglement. Nearly all of my fittings must be oriented in particular ways. It's kind of like when you put on an ell it needs to end up pointing a certain way, only there are a lot of joints in a few cubic feet. I can either stop at a certain point or make another full turn if it seems too loose. So I need some advice on how to decide when is tight enough. In today's efforts I always went another full turn. Did I overdo it? Nothing cracked!
 
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Old 03-08-14, 04:37 PM
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TFE tape is used to lubricate pipe threads, not seal them. Pipe threads by definition are an interference fit. If all your connections are leaking and you tightened them sufficiently then I suspect the threads are cut too deep or too far. Are all the fittings from the same kit or supply house? Could be a bad production run.

Pipe dope on the other hand can be used to help seal a balky fitting that leaks. But again the threads must be cut properly to begin with. I use to work with 150# and 300# pressure pipe systems and we never used tape or dope. Extreme tightening was all that was needed.

Not to insult your intelligence or your experience but are you sure they were all NPT/FNPT threads?
 
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Old 03-08-14, 04:57 PM
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I am not insulted. (Yet - though it is possible! )

I bought all of the fittings and nipples at the Home Depot, so they probably come from all over China, not just one plant. I'm sure they are all standard NPT threaded. They are all tapered and all behaved as NPT fittings always have when I have used them before.

Not all of my connections leak, but so many do that there will be a significant amount of disassembly to correct them all.

So I tightened my 1" fittiings by laying a 15" pipe wrench on its back on the ground to cradle the fitting and then turning the nipples or the fitting on the other end of the shorter nipples with a 12" pipe wrench. This allowed me to push down with a substantial portion of my 200 pounds if necessary. Some of the joints were so tight that I was afraid they would break. But on others I stopped short of that because I knew I couldn't get another full revolution on them and I needed the components to be oriented correctly. I am making a manifold for some irrigation valves and I would like them all to be sticking up in a row, not some tilted this way or that or buried in the ground.

Since the tape didn't work, I have two choices: pipe dope or just clean them up and use epoxy to make permanent joints. Which should I try next?
 
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Old 03-08-14, 05:43 PM
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I guess that's why irrigation systems are specially manufactured just to avoid this type of problem.

OK. Have you looked at using Pex pipe and/or Sharkbite fittings and vales? Probably too late since you bought everything already.

If it was me I would try the dope first and then the epoxy. If the dope don't work try Rescue tape




I know a guy who used rescue tape on an isolation valve under his sink as a temporary fix. It's been fours years and still holding.


If the manifold is steel and not brass then I would crank down even harder on those fittings.
 
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Old 03-08-14, 05:55 PM
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How much tape are you putting on?? Probably too much...

I do 5 turns or so of tape. Moving up the threads then back down in 5 - 7 turns.. Also after I tape I use a light coat of teflon paste on top of the tape...

I only do that on say large diameter pipe or troublesome joints...

Also I have had trouble with the threaded pipe/nipples from china.. As of late I have been using tape and paste as the tolerances are whacked out IMO...
 
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Old 03-08-14, 06:14 PM
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I think if you will check you will find that it seems a great number (maybe the majority) of plumbers use dope on top of tape. (Seems like Mike is one also.)

That blew my mind, I thought I misunderstood. But no. I think you will find that is the case.

So I started to use several turns of Teflon tape with RectorSeal #5 on top of the tape. Then I really tighten it up. Really tight.

I’ve done that with many one inch pipe connections and never had a drip.
 
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Old 03-09-14, 09:53 AM
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OK, tape then dope it is. I was in the Home Depot last night to get some dope and McGuyver was there. That's his nickname and for good reason. He's an old guy who can solve virtually any problem. He said to use tape then dope, too. So that seems to be the majority opinion, thought it will probably never be completely agreed on by everyone. I will try it and I will crank down even harder and if anything leaks after that I will use epoxy. I am building this thing to outlive me and if it needs to be changed in the future it will probably be because someone buys the house and wants the irrigation done differently.

Thank you all for the help.
 
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Old 03-10-14, 11:52 AM
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really wanna go nuts with no leaks use some blue block sealant over tape lol. Get it right the first time......
 
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