Compression tube fittings for brakes

Ron Earp · 04-09-05, 02:51 PM

I'm plumbing brakes for another race car and I was wondering about the use of stainless steel compression tube fittings for coupling and teeing lines.

I've got two very difficult places to work in that will require me either to flare the line on the car, really hard to do, or use a compression tube fitting. I've used these things before when I worked at Dow Chemical and they'll hold a lot of pressure and didn't leak. But, I've not used them in brake work - any comments? I was thinking of using a 3/16" stainless steel tee, basically you cut your line off square, push it into the fitting, then tighten the hell out of the fitting which should make it leak tight.

R

Richard Timte · 04-09-05, 04:50 PM

Ron,

IMHO you should only use 45% double flare or 37% AN flare fittings in a brake system. I tried to use a compression fitting while stranded on the side of a road when I was a kid. It just spit fluid all over the place. I just think that you should not take the easy route what it comes to brakes.

Trevor Booth · 04-09-05, 05:22 PM

Ron,
There are many variations to the compression fitting range. I would suggest you speak to a local manufacturer although it may be difficult for you to get a recommendation from them as it is automotive use of an industrial product and you would be aware of current consumer legislation dramas.

In my experience, with industrial use, compression fittings need to be well supported in an environment of vibration.

I would tread cautiously.

DaveWharran · 04-09-05, 09:25 PM

Ron,
If I were to use compression fittings, I'd use Swagelok brand. If....
We use them on air, steam, water, hydraulic, etc. at work with great success. They use a double ferrule design that you do not tighten until it wont go any further. There is a spec for tightening amount.

They indicate that the pressure rating on the fitting is either the rating of the tubing or of the pipe thread if it is an adaptor type fitting.

We use 316 stainless fittings and tubing and typically have few failures due to vibration.

We typically don't have anything that exceeds 2500 psi or so. You may want to dig into max pressure ratings on the appropriate tubing and any legalities by either DOT or the racing santioning body.

See Swagelok data at
http://www.swagelok.com/downloads/we.../MS-01-140.pdf

They aren't an inexpensive fitting!!

Dave

Ron Earp · 04-09-05, 09:58 PM

Dave, this is exactly what I have and what was at Dow. We had a special wrench at Dow that you set for various tube types, but, in the end I found you could tighten the hell out of them and it didn't matter. We had some stuff at 11,000 to 12,000 psi and it didn't have problems. The ones I have now are something like 32.50 a tee, but it would really come in handy in this spot. I can flair and do that, no problem, but I'm trying to clean up another persons mess and this would solve the problem unless I wanted to run new lines throughout the car.
R

Phil · 04-10-05, 11:56 AM

Ron
IMHO compression fittings on brake lines are really scary. OEM stuff, while utilitarian and not too nice looking, seem to last a long time, mostly rusting along chassis rails or suffering an impact is a cause for failure. I suggest you look in McMaster at the JIC (37*) fittings. They work well,with stainless and seamless lines, have a single flare with a little backup sleeve (rather neat), and are rated at 2500 psi or so. I think just about everything you may need is available, Tees, Ells, 45*, etc.
Good luck
Phil

Ron Earp · 04-10-05, 12:07 PM

I don't really like them that much either and it looks like I'm pulling the line out and re-doing the whole damn thing. I can flare and mate just fine now, but not in the area that this line would have to be fixed.

R

David Tickle · 04-11-05, 12:30 AM

Ron

We use compression couplings at work too. They are wonderful providing the tube is undamaged and completely circular. Typical brake pipe has been coiled at some stage of it's life and may not be circular.
Another point, working from memory now, but I think for the UK, the SVA rules forbid such couplings. It's about 4 years since mine was SVA'd.

Regards

Dave Tickle

cossiemetro · 04-12-05, 05:07 PM

we use s/s compression fittings at work (oil refinery)and they can take huge pressures upto 40+bar