Jon,
I stand corrected! The compression fittings I have always picked up at the
local auto parts store are of the type on page 123 commonly called Swaglock
fittings and it was those I was quoting the numbers on (some times they have
them in steel as well as brass). The only time I have used the type with the
barrel shapped ferrel is on plastic tubing and in larger sizes under the sink.
I guess I will jump on the band wagon and state that if you are going to use a
compression fitting it must be one designed for high pressures and have the
tapered ferrel not the low pressure barrel shape. I would be suprised to see an
auto parts store selling the low pressure ones in break lines sizes. :\
It's great when you learn something and I learned you need to pay more
attention to what you use.
Dave Clement
99 SLT+ CC 4x4
In article <d6rarj$hjd$1@bent.twistedbits.net>, jon@dakota-truck.net writes:
>
>
> david.clement@verizon.net wrote:
> : Just to make sure I wasn't going to get egg on my face I checked the
> : McMaster-Carr catalog and the common brass compression fitting for 1/8 or
3/16
> : tubing is the numbers I quoted below. We used to use a compression fitting
that
> : was brass with a plastic ferrel that was designed for plastic tubing that
would
> : seperate at 500psi in 1/4" size but I have never seen as small size fitting
> : that was rated for well over 1000psi. Even 1/2" PVC water pipe is rated for
> : 300psi.
>
>
> Page 121: http://www.mcmaster.com/nav/enter.asp?pagenum=121
>
> The general purpose brass compression tube fittings in 1/8 and 3/16
> are both rated at only 400psi. While it is true that the "self-aligning"
> type (with a built-in ferrule) are rated for 1900-2800psi, I have seldom
> seen that type in a hardware store; if you ask for a compression fitting,
> you'll get the type with the separate ferrule. Somebody who goes into
> their local Ace Hardware or Autozone and thinks they are getting a fitting
> rated for 2,000psi may be in for a nasty surprise.
>
>
> : I have been using this type of compression fiting for 30 years for break
line
> : repairs and the brass ferrel easily deforms the carbon steel used in brakes
> : lines and have never seen one fail that was put together properly (the most
> : common mistake is the tube not being fully seated in the fitting resulting
in
> : the ferrel not deforming the tube an locking in). Also, keep in mind that a
> : 3/16" brake line has about a .150 bore which works out to .0177 sqr inches
of
> : cross section, even at 2000psi operating pressure that is only 35.5 lbs of
> : force trying to force the tube out of the fitting, the brass it self is
much
> : stronger than the because of the mass than the actual tubing.
>
>
> Your calculations appear to be correct, but since the manufacturer of
> the fitting has basically stated that it is effectively only rated for
> 7 lbs in that situation (400psi), I'll be a big wuss and stick to 45 degree
> double flared fittings for my brake lines. :-)
>
>
> : As for the quality of what you purchase at Autozone! What makes you think
the
> : steel line you get there is going to be any better?
>
>
> I didn't word that very well; I wasn't meaning to imply that the
> fitting is of inferior quality since it comes from Autozone, I was
> referring to the fact that at hardware and auto parts stores, usually
> these things are thrown into bins and not individually labeled.
> Probably the only thing the store is going to be able to tell you is
> the price. In such a situation, you're essentially buying "anonymous
> fittings"; there is likely no way to determine who the manufacturer
> even was, let alone the manufacturer's recommended pressure limits
> for that particular item.
>
>
> --
> -Jon-
>
> .-- Jon Steiger ---- jon@dakota-truck.net or jon@jonsteiger.com --.
> | 1970 Barracuda - 1990 Dakota 'vert - 1992 Ram 4x4 - 1996 Dakota |
> | 1996 Intruder 1400 - 1996 Kolb FireFly - 2001 Ram QC 3500 CTD |
> `------------------------------------ http://www.jonsteiger.com --'
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