Loctite To Seal Air Leak?

First, establish the source of the leak. Could it be a gasket leaking into the threaded hole. Most holes are blind, and do not enter the pressurized part of the system.

In any event, the system will have to be de-pressurized and repaired.

Teflon tape should have worked, if used properly, and the leak is "below" (on the pressurized side of) the tape.

Loctite should work fine. Use a grade that can be taken apart, if needed.

How much pressure?

About 9 bar.

Exactly my thinking.

gussosa, a picture of the leaking connection would give us a much better idea of what you're dealing with !

There isn't any flange. The air is leaking through the full threaded Allen bolts that hold in place the discs of butterfly wafer retention valves

This makes no sense.

Where, exactly is the leak?

Does the valve look like this?

What does the supplier, whom you have not identified, say about sealing the valve ?????? What's the valve P/N???

You can't possibly be the first to encounter the problem.

Maybe a picture, to get over the agony of 20 questions!!!!

Check this picture:

Find out just where the leak is coming from but you have learned what most learn that teflon tape is useless and causes it's own problems. The semi liquid sealer used on gas fittings works as good as anything that has threads, it comes in a tin with a brush on the cap and is usually a grey color. The other comments concerning the treads having access to the pressure are correct but who knows how the flange was produced?

But it does not work as a thread locker, so in some applications PTFE may be a bad choice.

This is why I suggested Locktite as they manufacture a wide range of both sealants and thread locking solutions.

However, as others have pointed out, there may be other reasons why the assembly leaks and sealing threads may be simply a Band-Aid approach rather than a true fix.

uh...you say "This is why I suggested Locktite"

but lyn suggested it first in post #1 AND he spelled it correctomundoly

. . . "GA" lyn

http://www.loctiteproducts.com/

Misuse is not the fault of the tape.

Most of your "examples" are indeed caused by careless, untrained, uncaring operators.

Teflon is an inert substance and will not contaminate liquids. If there are bits of it in a system, it isn't the tape's fault.

Following your logic, we should melt down all guns, because they kill people.

I have nothing against guns since I never found a gun damaging a servo valve or any other part of a hydraulic machine. Nor have I found scraps of a gun in any of these machines. On the other hand________________

You have ask how often do we hear "if used properly"? Really? How else do you suggest we use them? And as Lyn suggested, if you're getting contamination of PTFE tape into your process/equipment then whoever applied the tape didnt do it correctly, plain and simple. If your local gas company doesn't allow tape good on them, there are thousands more that do and it works perfectly fine for them in the right application. If you're ham fisted in your application of paste you can suffer the same issues with contamination of process and/or equipment. Been there, done that. In my line of work we use predominantly tape (and occasionally paste when specified) on NPT connections up to (and sometimes over) 2,200psi on oil & gas equipment. The only issues we encounter are poorly formed threads not sealing correctly or excessive vibration causing threaded joints to loosen over time.

It appears that one comment keeps coming up and that is ( if used properly) these comments are a strong indication that the tape is poorly designed to require such attention to detail during proper use. Yes the paste can be over used and probably is but since it will dilute in oil for instance there is less chance of locking up a hydraulic valve where the tape is a solid. Even removing a threaded pipe can leave particles in the parent pipe, there is just too much probability of error not to ignore the contamination issues. I suggest, do as you wish which is what the sales engineer mentioned that being, old habits are hard to change even when mandated or a better product is introduced. Cheers and good luck.

Probably the most sensible thing I've seen posted in this thread......

Surely since this (CR4) is supposedly "The Engineer's Place" it's participants would be interested in performing the task properly everytime?

Well,

It gets crazy sometimes: 2

I'm one of the worst.

OK, so by your rationale, PTFE paste is poorly designed as it can be over-used as well? You can use any tool or item incorrectly if you put your mind to it, doesn't mean that tool/item is poorly designed.

If someone doesn't possess the skillset needed to use the tool/item properly then leave to someone who does.

Roy, Teflon tape has been used for many years in the plumbing industry. I've used it for decades and most of the time it works great. The times it hasn't is my fault (too much or too little tape was used).

Lately, I've been using a teflon paste. It's a little messy to use, but I haven't had any problems. It also is more expensive, but time is money and I prefer doing the job once and not having to redo it, because I didn't use enough teflon tape (or worse, I used too much and damaged the female side of the fitting).

Teflon tape - used it for 11 years every time I had to go into a pressurized gas well with a tool. (several hundred rig ups in that time) Some were as high as 4200 psi. Leaks were not a problem.

Threads can cause "virtual leaks" when used inside HV and UHV vacuum systems. One cure is "vented screws".

Just so you know I'm not pulling your http://www.uccomponents.com/

That's why we have to know what your talking about.

I don't think you should put locktight on those bolts. Put a seal gasket under the heads instead. That is to say, a rubber washer to seal, a metal washer to distribute the pressure, and a slightly longer screw to ensure thread contact. Such an installation will not void any warranties and if it doesn't work, you are back to square one.

You have a problem of compressor vibration

To solve the thread leakage/tightening - use Loctite-638 (good results !!)

Or use a sealant adhesive: JRTV's S/W-460 (or equivalent)

On pressurized aircraft we use PPG PR-1422 B-2 as a fastener and feed-thru hole sealant.

Of course this is usually sealing to 8-10psi differential and you don't mention your psi requirements.

Hooker

Teflon tape is generally designed to work on tapered thread situations, as in most pipe thread fittings. Non-tapered bolts have too close a tolerance and might strip away the tape as the bolt enters the hole. You can verify this by removing the bolts and see if the tape is still on the threads or not.

There are heavy duty versions of the tape, usually yellow or pink. (I think the yellow is for gas applications.) I prefer them because they have more body and allow for adjusting the angle of Tees and such.

Common loctite is designed to lock threaded bolts in place in case of vibration, not seal them.

I've heard that teflon joint sealant is better than tape, but it is messy, and I personally prefer the tape.

In your case, I would recommend silicone sealant. If it is a hot environment, HT silicone. That should contain most pressurized air unless yours is unusally high.

Again, Loctite makes a rainbow of sealants and adhesives. not just the two colors found in auto stores.

Loctite has specific formulas for all kinds of needs including pressure sealing threaded fasteners.

It must just be me, but I think nearly everyone has missed the point...... There should not be a parallel thread being used to retain compressed air unless it is designed to work in conjunction with an appropriate seal/washer (ie BSPP). The OP needs to locate the source of the leak and rectify it rather than just try and "band aid" the leak by plugging the threads up. There will be a failed or faulty component, there's no point speculating what it is without more info from the OP.

The first sentence of the first response, "First, establish the source of the leak." indicates that this was thought of early on.

Air tight seals can easily be established between two unthreaded sleeves if done properly. So, while non-tapered, straight threads may not be ideal for sealing against air, it is still easily accomplished, done properly.

AH had a point that PTFE tape is not a thread locker, and may have been mis-applied here, but OP has failed to adequately define the problem.

Everyone has a favorite, can't miss product, and most offered here have simply further clouded the issuee.

Suggesting Mac-Master Carr and Loctite indeed further cloud the issue unless you know how to select adhesives, AND PROPERLY PREPARE the surfaces for use.

Let's back off and force OP to give us something to work with, other than speculation.

Our answers were based on our experience with mentioned Loctite/JRTV Sealants...

.... Meaning; pressures and vibrations (like shell firing in AM case....)

All other mentioned by you procedures are "a must" to any solution required

look here:

http://www.mcmaster.com/#thread-sealants/=orwurz

If it is available in your country, a product called Leak Lock by High Side Products has a little more body to it and does real well in a lot of cases. It is intended for the refrigeration industry and is not thinned by oils but by alcohol. I've used it on a lot of things - compressed air, gasoline fittings on a car and refrigeration applications. -- JHF

Teflon tape works well on tapered pipe threads which allows the tape to be clamped in the connection as it is tightened. Although I prefer teflon joint sealant, the tape works well. I had one connection that I could not seal (probably poorly cut threads) and took both the teflon tape and the teflon joint sealant.

It is improbable that either or both would work on straight cut bolt threads as there is a spiral gape that does not close as the bolt tightens.

Why not just use self sealing screws like here or Zago? They make air specific sealants.

Thank you for answering the question directly.

I'd skip directly to old salt's last paragraph and follow those directions.