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Old 08-04-2015, 08:43   #16
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Re: Pipe Dope Instead of Teflon Tape

You over tightened the pvc fitting. It happens all the time. The pipe dope is superior to the teflon tape. But at the same time you can over tighten with the pipe dope as well. Sometimes it's just a hair line crack that is barely visible. When using the pipe dope only fill the valleys in the male thread and you will get a good seal. You don't have to crank it down super tight to get a seal.

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Old 08-04-2015, 09:14   #17
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Re: Pipe Dope Instead of Teflon Tape

Originally Posted by sailjumanji View Post
I am reassembling a circulating water system for A/C. March pump has a 1/2 inch threaded male discharge, that I attached a 90 degree Speer PVC1 fitting with hose barb. I wrapped the discharge fitting with Teflon tape, and screwed on the Speer fitting, but overtightened and cracked the fitting. It's a fine balance between putting enough tape on the threads, but not so much that it cracks the fitting. Anyway, a marine A/C guy recommended using pipe dope instead of Teflon pipe. He said the dope is the only thing that allows you to back off a fitting (to get the orientation right), but still seal. Anyone using a product like this? Am hoping something available that is not as messy as traditional pipe dope, and I really don't want to deal with grease on everything. And it needs to stay pliable so that it can be disconnected when the pump needs maintenance. Recommendations?

My backup plan is that I have purchased several of the Speer replacement fittings, so can Teflon tape it, and hopefully not break again! I am fighting a PTF code issue and don't want to admit how many times I have reassembled the system.
[I'm borrowing from a recent post of mine on Attainable Adventure Cruising...]

Since I learned about it from a machinist/diesel mechanic 30 some years ago, I have always carried and never been let down by Permatex® Form-A-Gasket® No. 2 Sealant [NON-Hardening; NOT the Hardening version…] I use it for any threaded pipe connections of all materials [even nylon and marelon on occasion…] and sizes for any liquids or gasses typically found on a boat. And I can attest that the joints disassemble readily years later, and never leak.

It is readily available here in the US from most automotive parts and hardware stores.

TDS and MDS available at:
Gasket Sealants : Permatex® Form-A-Gasket® No. 2 Sealant

Of course it is also useful for its original purpose as a gasket compound for replacing or helping seal gaskets on engines, fuel tanks, etc. In my experience a tube will last for years [10 and counting on one…] if kept tightly capped.

Note that this is not a modern, silicone based super high-temp gasket compound… This is old style black goop similar to roofing mastic in appearance…

And like all goops if this ilk, your degree of meticulous application is inversely proportional to how much of it will mysteriously appear on everything imaginable when you are finished with the task at hand… (But it cleans up readily with isopropyl alcohol or waterless hand cleaner.)



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Short on opinions; focused on research, facts & experience [yours and ours...]
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Old 08-04-2015, 09:15   #18
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Re: Pipe Dope Instead of Teflon Tape

Lowe's or home depot has pipe dope in the plumbing department that works on water and gas lines (read diesel) which is easy to apply and relatively mess free. I think the dope is easier to apply than tape.

You cracked the fitting because the tape reduced the thread friction allowing you to easily over tighten.
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Old 08-04-2015, 09:57   #19
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Re: Pipe Dope Instead of Teflon Tape

You don't want to use pipe dope on hydraulic hoses or fittings. Pieces can break lose inside the hoses or fittings and cause damage to pumps and valves.
Don't over tighten your fitting, don't over wrap with tape. Put tape on in a clockwise manner.
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Old 08-04-2015, 10:04   #20
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Re: Pipe Dope Instead of Teflon Tape

I'd try using TFE teflon based pipe dope . Its good and thick, won't dry like a rock. Fittings come apart easy. Always worked good for me .
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Old 08-04-2015, 14:37   #21
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Re: Pipe Dope Instead of Teflon Tape

In my experience, it is very rare to find a situation where Teflon tape is a better choice than pipe dope, not to say they doesn't exist, just rare.

The thing I see very often is using tape or dope where none is required or useful, such as flare fitting and compression fitting where the threads do not do the sealing.

Note the green seal area in attached, tape or pipe dope on the threads will do nothing here.

Lots of hydraulic and fuel fittings are these type.

In this case sealant can be use on the NPT side but not the flare side.

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Old 08-04-2015, 15:32   #22
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Re: Pipe Dope Instead of Teflon Tape

Maybe I should start this response with "Don't Try This at Home."
While Buddy boating, the diesel fuel line broke at the fitting on my friend's engine, and he didn't have any spare ferrules. Using Teflon tape, I made one for him, and our travels continued without mishap. Ultimately we separated, and when I saw him a year later and asked when and where he replaced the Teflon, he said he never did and made the point, " why mess with something that was working."

And for those who flare copper tubing rather than using ferrules, in an EMERGENCY, where the tubing cracks at the flare's surface, Teflon tape can judicially be wrapped around the seating surface of the fitting (not covering the orifice), the fitting can then be reconnected, and hopefully the leak will have stopped. And yes, I have tried it, and it has worked well.

I carry aboard Teflon tape, Teflon based pipe dope, and Permatex #2, but I prefer to use Teflon tape, and while EVERYONE including manufacturers will tell you not to use Teflon tape on diesel fittings, I have used it without fail for years. The "trick" is to start winding at least one thread back so no tape enters the system, because that is what it is all about. However, I strongly recommend you follow all the manufacture's instructions so as not to void any warranties. As for me, by the time I get around to installing the product, the warranty has usually expired months ago.

Finally, I find Teflon tape easy to use, and easy to clean off threads if the parts have to be disassembled.

Oh, one further note: Teflon tape comes in different thicknesses. I use the heavier grade for larger pipes.

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Old 08-04-2015, 15:43   #23
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Re: Pipe Dope Instead of Teflon Tape

Thanks svjennie I feel I have learned something here.

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Old 08-04-2015, 15:51   #24
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Re: Pipe Dope Instead of Teflon Tape

Originally Posted by ben373 View Post
Thanks svjennie I feel I have learned something here.

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Since there are some conflicting posts, I am curious as to what you have learned.
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Old 08-04-2015, 15:59   #25
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Re: Pipe Dope Instead of Teflon Tape


I have been waiting for a thread to appear for which I could respond with some degree of technical authority. This may be my one and only hope, so please be kind.

When I first started my apprenticeship, the pipe dope versus Teflon tape debate was an important part of my training as an outside machinist.

Short answer: pipe dope is better at stopping leaks and does a swell job when properly applied.

Long answer: Teflon tape has a few purposes but why it works is as important to understand as is how to apply it correctly. Most do not use it right or so said my mentors. What it does is reduce friction. That allows threads to seat further into the wedge. It also stops galling (meaning metal on metal seizing) so that assemblies can be taken apart at some future point.

To proper apply Teflon tape, it must be wound such that the wrapping tightens as it is inserted into the female threaded part (nut, tapped hole, cap, etc.) One and a half wraps is all that it needed, (manufacture spec) because using any more than that becomes packing. Excess packing reduces the amount of room that the threaded parts need to seal and actually lessons the ability of the joint to seal (more on this latter).

Rather than blindly accepting the opinions of our mentors, we noobie technicians actually conducted experiments. Lots of experiments! Teflon tape does work on machine screws (straight threads) as well as tapered threaded assemblies. The reason this is true is because as the assemblies are tightened, the interface between the treads of the fasteners actually deflect.

The threads themselves are bendable (if only slightly). What gives them their gripping force is Mr. Inclined plane. The threads are literally wedging a tapered shaft into a valley. There is an air gap between the peak of the male thread and the valley of the female trench. But it is the side to side surface tension that seals the two surfaces; the side to side contact of the threads (the force of surface tension) is what makes the threads hold fast.

Adding pipe dope also decreases surface tension so it allows the threads to be tightened further. Exactly where in the system of thread to thread contact that the most friction is created is not easy to judge. So we used bluing agents to study the interfaces after partial and full assembling.

The friction could be in the middle, or towards either end of the fastener but also on the tips, center, or nearer to the roots of the threads themselves. Adding a lubricant like Teflon tape, or pipe dope, eases the tension of deflection in the joint and smooths out the distribution of tension so that more side to side contact occurs (meaning over a greater surface area).

Which is better is somewhat dependent upon the purpose. But for us, we used both strait threads and tapered threads as well as capped tubes and pipes of various sizes in our test samples. These were put under water pressure and allowed to fail. We tested properly torqued assemblies, over torqued, under torqued, and all of the above with combinations of Teflon tape, pipe dope, and both pipe dope and tape. We tested no wrap, over wrapped, properly wrapped, and under wrapped, as well as thin, correct, and too thick of pipe dope application.

Then we intentionally damaged the threads in various ways and repeated the tests. It took a full week to do all of the tests but the longer term examples stayed in place for months and even years. We had a pipe shop with calibrated pressure instruments to use to monitor the assemblies. Some of the tests from previous year's classes had stayed under pressure for 10 years; they let us take them apart just to teach us the differences.

To me, pipe dope is the clear champion against leaks. I know this because I filed a groove into the entire thread length of a tapered assembly and tried my best to seal it with torque, (epic fail), then Teflon tape, (serious leakage) and then pipe dope (winner). I even made runs with tape and pipe dope but that too leaked rather quickly. To my surprise, the pipe dope only samples held for weeks even though there was a complete channel filed into the thread of the male part of the fitting.

By the way, over torqued consistently failed sooner than proper torqued joints but adding tape, or any other lubricant such as grease, does change the amount of torque that needs to be applied or else thread damage can (and did) occur.

You are welcome to repeat your own analysis, but the results will probably not vary. At least they didn't for my class, or the ones before mine.


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Old 08-04-2015, 16:03   #26
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Re: Pipe Dope Instead of Teflon Tape

I've gone from tape to pipe dope over the years, but have now gone back to tape for a lot of things. I've never broke a fitting due to tape. You need to put 3-5 wraps of tape on I've found.
The pipe dope is very messy and looking at old dope , it turns hard and crumbles... not sure what it does inside the joint.... I'm talking about white Teflon dope.
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Old 08-04-2015, 16:14   #27
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Re: Pipe Dope Instead of Teflon Tape

Thanks so much for the post. I learned from your professional knowledge.

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Old 08-04-2015, 16:38   #28
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Re: Pipe Dope Instead of Teflon Tape

On a boat we sometimes want electrical continuity in the piping system (metal pipes and fittings of course). Pipe dope is the clear winner here.

If I was only able to have one or the other on my boat my choice would be pipe dope. Teflon tape is not to be used on fuel line fittings because it can break off and flow through filters or other critical parts.
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Old 08-04-2015, 17:03   #29
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Re: Pipe Dope Instead of Teflon Tape

Many opinions with little substantiation to justify one or the other or systems where they can and can't be used.

I'm with the "either can be used effectively in the right hands of a particular job" crowd.

Know you and your equipment/materials limitations and trudge along.
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Old 08-04-2015, 17:25   #30
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Re: Pipe Dope Instead of Teflon Tape

While I still carry Teflon Tape on board, I find that I use it infrequently. Thread sealants (in my opinion) seem to be longer lived and a better choice in almost any application.

Currently my favorite is Blue Monster Industrial Grade Pipe Thread Sealant - a slow drying, non-hardening sealant that is NSF listed and useable for just anything short of oxygen tubing. I have used this for about 10 years and have found it to be very reliable. I have never had to remake a joint, and it will allow dis-assembly.

PTFE Thread Sealants and Thread Seal Tape - Blue Monster Products

By the way, I am still working off the same 4 oz. container after all this time. Use sparingly for best (and tidiest) results.

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