Technical sealing pipe thread on brake fittings

Yep, don't let the tape get onto the end of the fitting where the threads will cut it off and let it go 'someplace' and you won't have any issues. I also use it on wheel cylinder/caliper bleeder screws both for anti-seize reasons and to help seal the threads when bleeding brakes with a suction bleeder. That makes the bleeder work a hell of a lot better. I also use it on flare nuts, but there it's just for the anti-seize properties.

The problem with the liquid sealers is they tend to harden over time and the anti-seize properties can go away. Plus it's a PITA to clean off. Teflon tape is unaffected by time...

 

NPT is standard pipe thread. NPT "F" is DRYSEAL pipe thread, both seal by interference, NPTF being a slightly different configuration and much more precise (see @Oilguy note above).
Teflon tape and most 'thread sealers' don't do the actual sealing, the thread does. What they do is provide some 'lubrication' to allow you to get the fitting tighter, increasing the interference fit. Go easy and carefully when tightening when using either one, as it's easier to overtighten and crack something. Liquid 'sealant' works best, Teflon tape in a pinch. In booth cases, keep it back 2 or 3 threads from the end (remember, the thread is tapered, so the first 2 or 3 threads are basically 'lead-ins', and don't really come into play until the fitting is fully tightened).
And don't be afraid of pipe threads: look at all the high pressure steam systems that use them, not to mention old hydraulic systems.
What we now call AN fitting were actually developed prior to WW II by Parker Hannifin who convinced the U.S. Joint Industry Council ( a WW II era industrial advisory group) to adopt that configuration in order to standardize components (and ease assembly/disassembly) used on military equipment and vessels. In the industrial world they are called "J.I.C.", and are usually less expensive at an industrial supplier than an automotive supplier.

 

Forgot to mention... 45* double-flared fittings are typical in brake and fuel lines and have been the standard for nearly 100 years (I know...OT stuff has bubbles, whoever the hell bubbles is). They (as we all know) seal by means of a tight metal-to-metal facial contact (not THAT kind of facial, you pervs!). One of the main reasons for DIY sealing issues is OVER FORMING THE FLARE! Don't crush the flare and tube: stop just short of collapsing the flare, seat (and form) the flare by tightening the fitting/tube assembly into the mating part. This forces the metal flare to conform to the fitting and part, rather than a third element (the flaring tool).

 

Not sure what braking system runs at 5 or 6 PSI. Residual pressure for drums is around 10 PSI, and pressure under hard braking can be north of 1000 PSI.

That photo had to be taken in the marketing department.

 

If you plan is NOT to remove the fitting-- hardening over time should not be an issue. If you need for some reason replace the fitting--- start with a fresh one-- no cleaning necessary. I dislike NPT threads and much prefer ORB or AN with a seal washer-- no sealant involved

 

I've used Locktite 545 on the 1/8th pipe fittings in my brake kits for many years, used to include a small tube of it in my brake kits. If everything is clean and dry and it's allowed to set up and dry it will usually never leak

 

I guess I left the fuel line part out on that one.
One response mentioned it.

 

Frank's hot sauce, i put that shit on everything

 

I use teflon tape on both brake lines and gas lines. But the key is to not wrap it to the ends of the thread, so I stop short of the ends. If it's not over the ends, there's no way the teflon can get inside the brake or gas line.

 

did a lot of work on high pressure washers[2500 t0 4000 psi] manufacturer wanted red or blue loctite on pipe threads only-when complaining about quality of pipe threads,there is 3 or 4 manufacturing standards of "fit" depending on intended use

 

P.S. one of the best educational tools for info like this is a McMaster catalog!!!best bathroom reading ever

 

The need for a sealant is why there is a aversion to using tapered pipe thread, you do not want to rely on Teflon tape or other PTFE sealants for brake fluid.
If you have no choice use Loctite on the thread and give it time to harden before adding fluid to the system.

 

Tell Pete and Jake's that - they're through the frame fittings have pipe threads on the inside, That's how you hook up a tee or an elbow
Also, every proportioning valve I've ever seen has pipe threads in the end of it as well.

 

Wilwood calipers also have pipe thread. It's best to use steel fittings in them, not brass...

 

Yep, and a lot of folks use the steel NPT to AN fittings in either 3 or 4 AN for brakes.

 

Do you use it on flare fittings, like loctite's marketing department does?

 

So, I got the loctite 545 and it seems to work great on steel to aluminum or steel to steel pipe fittings.
One word of caution however, for some reason if you try to put an aluminum pipe plug or an aluminum pipe thread fitting into an aluminum hole with loctite 545, it will gall so bad that it will destroy the threads...bizzarre

 

Aluminum-to-aluminum, stainless-to-aluminum, and stainless-to-stainless threads of any kind should all use anti-seize of some sort. Recommended for aluminum pipe threads into iron or steel although that's not quite as touchy.

I've seen the first three mentioned put together finger-tight and then seize/gall trying to disassemble them...

 

I would think if your lines are double flared and tight you wouldn't have any leaks, HRP

 

Looks like the answer has been covered well here. In any flare fitting, the male and female parts of the flare are the sealing surface. A tapered pipe thread, the entire spiral is the sealing surface. The sealer is more about lubricant, than filling any imperfections in the surface.
One example; I spent a bunch on stainless brake lines years ago and had leaks. I reinstalled each fitting with pipe dope. Problem solved, although I knew the threads were not the sealing surface. The lube allows that fitting to be torqued much tighter with your same hand strength.

 

NPT threads are designed to use a thread sealant. Is it always necessary ? No not always, but it's a good idea. NPTF threads are designed to seal WITHOUT any sealants - typically used in fuel systems or somewhere where a sealant failure can be hazardous. YMMV
EDIT: For those suggesting that liquid teflon is a better seal than teflon tape I would say my experience has been the opposite. Where I once worked we had a few pipe threads (NPT) in a cooling system that had Propylene Glycol in it and ran around 1.5 Bar. I initially spec'd out liquid teflon because most guys would wrap the teflon tape on wrong and cause issues as a result. Initially everything worked great with the liquid teflon. A short time later we had a batch of fittings that were out of spec (the thread crests were much larger than the print allowed) the result was that after a very short time the liquid teflon would fail and cause a drip. My arguments to get parts to print fell on deaf ears and I was left to find a sealing method on the junk fittings as parts were already in the field. What I discovered is that the teflon tape, properly applied, was a far better Gap Filler than the liquid teflon was. I got to the point in my testing where I would purposefully cross thread a fitting and then seal it with the teflon - no problems. Keep in mind there are better grades of teflon tape and it does help to use the heavier stuff when things are "iffy". Again YMMV.