Compression Brake Fittings

[eamici]

Any input on using these vs. doing the how flaring kit process. I heard that the compression fittings are illegal in some states.

[Fixit]

My .02 - Do not.

Compression fittings are for the ice-maker in your fridge or the humidifier on the furnace... not for 1500+psi "life-safety" fluid connections.

[NAZ]

Use the right fitting for the job -- brakes are a safety system. There is no advantage using compression fittings and plenty of risk if one fails. And working with lot's of hydraulic systems over the years I've seen compression fittings fail.

[Matt K.]

My 2 cts: Depends on what kind of compression fitting you're talking about. Hardware-store varietyefinitely not. However, there's nothing wrong with a Swagelok-type of fitting in a high pressure hydraulic system. We use them all of the time for high pressure air and liquid lines. Never seen one fail. These are aerospace-quality fittings. The tubing will fail before the fitting does.

[GoDadGo]

Get This Tool & You'll Be Flaring Like The Professionals!

https://youtu.be/ftYuP-5jj4o

[Fixit]

Call me a dinosaur, but 100+ years of double-flare & taperseat hydraulic fittings trumps "quick & easy"...

[KegMechanic]

Never use compression fittings on brake lines. In a lot of states they wont pass safety inspection, regardless of quality. There's no need to buy an expensive hydraulic flaring tool. Pick up a cheap double flaring tool and some 3/16 brake line from the auto parts store and practice. You will be a pro in no time.

This one would work fine https://www.amazon.com/OTC-4503-Stin.../dp/B000L7QZ0Q


I recommend mounting the tool in a vice, this makes things much easier. Make sure you de-burr the inside of the line after cutting and I usually smooth over the outer edges with a fine file. Use a drop of brake fluid as a lubricant on the line. Make sure the wing nuts are TIGHT, so the line doesn't slip. Tighten the wing nut closest to the line first and then the other. Follow the directions and they should come out just as good as the factory flares.

And then you will have one more skill. Good luck

[mikeinatlanta]

I use nothing but AN, but agree with the post that there are other aviation fittings that would work and of course you can use the double flare. If I saw hardware store compression fittings on a kit car I would decline a ride due to overall concern with the safety of the car. If someone would do that where you can see, what would they do where you can't?

[mike223]

Double flares are easy + cheap enough.

There's nothing wrong with proper hydraulic compression fittings - examples Parker, Swagelok, Ferulok - rated for thousands of psi.


Absolutely not the ones they sell at hardware stores for icemakers, dishwashers, etc - rated for ~150 psi.

[David Williamson]

easier yet go to your local NAPA and pick up pre-made lengths of brake line in the length you need. The only home made flare fittings on my car are for the wipers
David W

[Bob Cowan]

There are some very good compression fittings available that will handle the pressure of your brake system, and a whole lot more. They are expensive. I see no reason not to use them if you want to. Cruise through the state inspection laws AND the DoT regs. If you don't find anything prohibiting them, go ahead and use them.

I wouldn't use them, but only because I am cheap. I can make a double flare for about $0.50.

[Avalanche325]

NEVER use compression fittings on a brake system. Yes, you can get them that are rated for higher pressure than a brake system. That does not mean that they are the correct fitting for the job.

One of the reasons that they are not the correct fitting is that there is no mechanical connection from the tube to the fitting. (Yes, some have a slight bulge in the tube when they are tightened capturing the ferrule, but it is not enough) This means that if the fitting loosens up just a little and you stomp on the brakes you can have a sudden and catastrophic failure.

If a flare fitting loosens, it will leak and you will hopefully feel it in the pedal, but because it has a mechanical connection (the flare is bigger than the hole in the nut) it won't suddenly blow out.

The easy way and the correct way are rarely the same way.

[mike223]

This means that if the fitting loosens up just a little and you stomp on the brakes you can have a sudden and catastrophic failure.

It really doesn't matter to me - I do not sell them, I do not own stock in any of the companies.

But you've got this wrong.

A proper hydraulic compression fitting (Parker, Swagelok, Ferulok, etc) is never going to fail in the manner you describe.

Proper double flares require some finesse, practice, + testing on the part of the operator.

Swagelok fitting installation for the novice: Cut tubing, debur, fully insert, tighten 450 degrees past hand tight.


Presto: The tube will burst before the fitting will leak (and if it works loose it is not coming apart, it will merely leak - just like a bad or loose flare).


https://www.youtube.com/watch?v=StGmh4g2Owk

[NAZ]

Compression fittings are very common in hydraulic systems – I’ve installed hundreds over the years, mostly Swagelok and Parker which are top of the line fittings. They are easy to work with and just as easy to install improperly and that’s where the problem is. I’ve never seen one fail that was properly installed but I have seen failures attributed to improper installation and these have completely separated immediately dumping fluid and pressure. On a punch press this usually does not cause any collateral damage as the pressure interlock simply shuts down the press. However, if a failure like this occurred on a brake system that could be a much more serious problem.
By using compression fittings you are departing from a standard used throughout the automotive industry -- using (or the plaintiff’s attorney may say misusing) a non-standard fitting on a safety system. If you’re not an engineer with a PE behind your title I suggest before you use compression fittings on a brake system you contact the manufacturer and ask them if they recommend their product for automotive braking systems. I’ve had the training, the experience, and tools to be very confident in installing compression fittings but would never dream of using one on a street car. Too much liability. I use inverted flare or AN fittings as these are common on braking systems. I also have the tools and experience to make my own AN brake hose and the means to pressure test them but I purchase brake hoses made to order simply as a liability safeguard.

So tell me again – why choose compression fittings over standard inverted flare or AN?

[mike223]

just as easy to install improperly and that’s where the problem is.

After further research, the typical tubing used for brake lines is not specified in Swagelok tubing datasheets and therefore is not certified for Swagelok fittings.

Here is the Swagelok tubing datasheet: https://www.swagelok.com/downloads/w.../MS-01-107.pdf

Anyone ever heard it called Bundy tube? https://en.wikipedia.org/wiki/Bundy_tube



Tubing alloys / manufacturing processes that will pass SAE J1677 flaring + flattening tests may not be particularly suitable for these types of fittings (and certainly do not appear to be certified).

[Boydster]

Aviation MS fittings are generally all compression fittings, and they run about 3000 psi... For many, many years. But you've got to have the right materials and the right methods. And MS is not cheap. With that said... I used all double flare.

[edwardb]

I've used the Swagelok compression fittings on SS fuel lines on several builds. Absolutely amazing quality. They are more than up to the task, to say the least, for the single digit psi of a mechanical fuel pump/carb or the 55 psi of fuel injection where I've used them. I like them because with a single fitting can go from the bare end of an SS fuel line to an AN fitting. Other solutions I've looked at require several adapters or a flare. At $15 - 20 each, they're not cheap. But cheaper than stacking up other fittings and they're just plain bulletproof. I got a chuckle out of the linked videos where the Swagelok guy was taking guesses on when the tubing would fail. Which it did at roughly four times the rated capacity and the Swagelok connectors didn't budge. Pretty impressive.

Having said that, as most have stated in this thread, they or an other compression fittings have no business in a brake system. Just my opinion, I'm actually pretty amazed how many forum members are afraid of making flared fittings. I can think of a whole bunch of building steps on these cars that are harder than that. With the right material, the right tools, and the right process, it's quite easy actually. I highly recommend the Eastwood tool already mentioned. It makes dead perfect flares in any material. Single or double, SAE or AN. Stainless is a little particular and takes some practice, but it will do it. Anything else you'll make perfect flares from the very first one. It's that easy. They're as good or IMO better than the pre-made flares. I've tried several varieties of the split bar assembly/yoke type common flaring tools. From cheap to fairly expensive name brands. None come remotely close. I see guys going to (again, my opinion) extraordinary measures (multiple pieces with unions, coils, etc.) to not have to make flares when with the right tool could be done without all that. At $150 - 200 (often on sale) the Eastwood flaring tool will be the best tool you ever bought. Worst case, buy it, use, and sell it. They get snapped right up.

[Ducky2009]

And while we're taking about brakes - Check with your state - Some states do not allow "Union" fittings in a brake line. Georgia does not.

[mike223]

Other solutions I've looked at require several adapters or a flare. At $15 - 20 each, they're not cheap. But cheaper than stacking up other fittings and they're just plain bulletproof.

I've tried several varieties of the split bar assembly/yoke type common flaring tools. From cheap to fairly expensive name brands.

Another note here.

I found that producing perfect flares / double flares in smaller tubing sizes (3/16") to be very easy with common split bar / yoke type flaring tools.

But nearly impossible to do well in larger sizes required for fuel / oil / accusump lines (the process pushes the tubing back through the vice).


I may have to try the Eastwood tool at some point.

In the meantime, I've found Swagelok type fittings to be bulletproof for these larger tubing sizes / applications.