Michael:
Your point is well taken and you've sent me scurrying into the tech notes
and applications data. What I'm finding is that Swagelok is getting more and
more into automotive and aviation applications, which are non-traditional
for them. With a little googling, I found app notes for SS helicopter fuel
systems and water-based hydraulic systems for automobiles (for HazMat
reduction), which seems to be a bigger deal in Europe than in the US at this
time.
I've sent off inquiries to Swagelok regarding the aviation and automotive
uses, particularly with respect to data on shock and vibration. Be
interesting to see what they have to say.
Hey, this is getting interesting!
Tony
----- Original Message -----
From: "Michael McBeth" <mmcbeth@peacock.ca>
To: "Tigers" <Tigers@autox.team.net>; "Tony McNulty" <t.mcnulty@ieee.org>
Sent: Monday, September 09, 2002 9:38 PM
Subject: RE: Brake Lines
Tom,
I specialize in instrument tube fittings but I wouldn't (don't) use them as
brake lines on a car. The reason tube fittings were invented was so they'd
be easy for unskilled people to put together, not because they sealed BETTER
than a flared system. There is a reason automobile OEMs still specify the
more difficult to install flared lines on brake systems. The problem
definitely isn't pressure ratings, as there is a four-to-one safety margin
on the working pressures you mention. Instrument tube fitting sealing is
plenty good; we seal high pressure (5000psi) hydrogen gas very nicely. The
issue that would concern me most is vibration, the Achilles heel of tube
fittings. Too much vibration and the tubing (not the fitting) will shear off
at the back of the fitting nut. This is particularly true of small diameter
tubing (1/8" or less), and bigger than that will give you a lot of brake
fluid volume. You'll also have to be extra cautious about scratches on the
tubing, since the sealing surface is the outside of the tubing (flaring uses
the protected inside surface).
Can it work? Yes, there are tube fittings on every natural gas powered
vehicle out there. We put ours on Hydrogen powered buses, but not on the
brakes. For my money brakes is not the place to scrimp or cut corners.
Michael McBeth
-----Original Message-----
From: owner-tigers@autox.team.net [mailto:owner-tigers@autox.team.net] On
Behalf Of Tony McNulty
Sent: September 9, 2002 3:23 AM
To: Bob Rice
Cc: Tiger Mail List
Subject: Re: Brake Lines
Bob:
Here's the skinny on the Swagelok tubing and fittings (from their catalog
data sheet):
"Fittings are rated at the working pressure of the tubing"
Rating In Accordance With ASME B31.1 .... multiply SS x 0.94
Size Working Pressure ASME
1/16 11,000 psig 10,340
1/8 10,000 psig 9,400
1/4 8,000 psig 7,520
Looks like a pretty decent safety margin. I know that SS316 is OK with
brake fluid. My concern is more for corrosion resistance (inside and
out) -- and appearance too, truth be told.
These fittings aren't the everyday bubble types that swage onto copper
tubing, they're more like a very thick washer with a tapered profile --
beautifully machined (probably why they're so expensive) really cuts into
the tubing wall when swaged on. The taper then seats with a mating interior
surface of the mating piece.
Let me know if you're really interested and I can send you a short piece of
SS tubing with one of these guys "installed". Otherwise, there's good
catalog picture info at their website.
Regards,
Tony
----- Original Message -----
From: "Tony McNulty" <t.mcnulty@ieee.org>
To: "Bob Rice" <Comanderbob@Comcast.net>
Sent: Monday, September 09, 2002 4:41 AM
Subject: Re: Brake Lines
Right on, Bob:
Definitely an engineer -- background in controlled fusion, particle
accelerators, pulsed power, and high-power microwave. The Swagelok stuff
isn't cheap, but it's forever. I have a pretty good pile of the stuff left
over from years past and will cobble together a tabletop rig to see if and
how it can be used for these kinds of pressures. I'm pretty sure they can,
based on some of the ultra-high pressure stuff I've seen for juice
pasteurization.
Tony
----- Original Message -----
From: "Bob Rice" <Comanderbob@Comcast.net>
To: "Tony McNulty" <t.mcnulty@ieee.org>
Sent: Sunday, September 08, 2002 11:54 PM
Subject: RE: Brake Lines
SOunds like an engineer to me. Where do you work? I've done some vacuum
projects before, but needed special high dollar fittings (2 torr) all
flanges and welded fittings
-----Original Message-----
From: Tony McNulty [mailto:t.mcnulty@ieee.org]
Sent: Sunday, September 08, 2002 9:02 PM
To: Bob Rice
Subject: Re: Brake Lines
Bob:
I'll look into the pressure ratings on the Swagelok fittings. Over the
years they've proven to be good in the opposite direction -- under really
high vacuum, and a leak is a leak is a leak. Maybe some tabletop experiments
can be done before anyone goes to a lot of time and trouble on this -- I'll
see what I can rig up.
Tony
----- Original Message -----
From: "Bob Rice" <Comanderbob@Comcast.net>
To: "Tony McNulty" <t.mcnulty@ieee.org>
Sent: Sunday, September 08, 2002 7:05 PM
Subject: RE: Brake Lines
Tony:
Thanks for the input, and the offer on the tubing. I'm still trying to
decide. I've heard quite a few opinnions. I've read that the pressure in
the brake lines can exceed 1000 psi (which is about right), (100 lbs foot
pressure over .625 dia .312 squared X 3.14159 = 24 lbs X 5 (lever advantage
pedal to clevis) = 120 lbs at fluid. + approx. 10:1 multiplier piston dia to
pipe dia = 1,200 psi.) and some say the only safe solution is "Bundy Tubing"
Of course if that was true why don't the break hoses explode? I like the
idea of SS tubing, which is what I ran for the fuel line. It bends quite
easy compared with brake lines. I also read several places that you should
never use compression fittings for brake lines. I believe that one,
although there's a tip on the web explaining how to repair a brake line, and
they use compression fittings. We use them where I work, and I don't think
they're rated over 500 psi.
-----Original Message-----
From: Tony McNulty [mailto:t.mcnulty@ieee.org]
Sent: Saturday, September 07, 2002 6:42 PM
To: Bob Rice; tigers@autox.team.net
Subject: Re: Brake Lines
Bob:
This is exactly what I'm planning. I propose to make my line from 304SS and
use SWAGELOK SS fittings and either Swagelok or Aeroquip. They have an
extensive catalogs and comprehensive websites at:
http://www.swagelok.com/
http://www.aeroquip.com/
Having said all that -- these guys are pretty high end and pricey (but
deservedly so) -- the result is "forever".
Not a paid employee -- just a happy customer. The SS tubing is readily had
from
http://www.twmetals.com/
the merged entity of the old Tubesales company. If you're on a budget and
you want me to, I can take a looksee on my next visit to the local metal
scrapyard and we can work something out -- last time there, they were
charging 50 cents/pound for SS -- but hey, there's no "minimum" on their
order. I'd take the high road on the fittings, though.
Let me know on the tubing.
Regards,
Tony McNulty
Weston, CT
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