Jon,
A common brass compression fitting for 1/8" tubing is rated for 3600psi and for
3/16" tubing it's rated at 2300psi, other are rated much higher. Even the
plastic compression fittings in brake line sizes are rated up to 400psi
depending on the plastic.
Also, I think you also over estimate the amount of pressure in a brake system.
I can leg press around 800lbs with both legs. Under panic braking it is
reasonable to assume maybe 500lbs on the pedal with one leg. I would
guesstamate the leverage ratio of the pedal is 2:1 so you are applying
approximately 1000 lbs of pressure on the master cylinder. Most master cylinder
bores are +/- a small amount around 1". Assuming 1" that is.785 in. sqrd or
785psi being applied by the master cylinder to the system. Well within the
pressure rating of the of a 3/16" brass compression fitting of 2300psi. Even if
the pressure on the master cylinder is 4 times it's still only 1570psi.
FWIW, the pressure rating on hose and tube fittings already have a safety
factor built in. Standard production testing is done at 1.5 times the rating
and design proof pressure testing is done at 4 times the rating (allowed to
leak but not fail on this test). It is safe to operate these fittings righ at
there maximum rating as long as you are still in the temperature range of the
fitting.
Dave clement
99 SLT+ CC 4x4
In article <d62d38$qtv$1@bent.twistedbits.net>, jon@dakota-truck.net writes:
>
>
> david.clement@verizon.net wrote:
>
> : Absoultly wrong! A compression fitting is every bit as safe as a flare.
Reason
> : the manufacturers don't use them is there are more parts and require more
> : manual labor to install them. The tubing will fail long before a
compression
> : fitting will seperate.
>
> : Years ago I worked in the lab of a company that made pressure transmitters.
We
> : used to setup test fixtures for pressure testing to 10,000 psi with
compression
> : fittings.
>
>
> Compression fittings can be used on high pressure systems
> (including hydraulics), but the fittings are usually steel or
> stainless steel and the ferrule design is different. Trying to
> use common brass hardware store type compression fittings on brake
> lines is begging for trouble; they have a max pressure rating of 100
> to 400 psi, depending on the tubing size which is (best case scenario)
> something like 5 times less that what you need in a brake system.
> If you use the "self aligning" compression fitings which basically
> have a sleeve built into the nut, you can get up to 1400-1900psi
> in the standard brake line tubing sizes, but that's not acceptable
> either. There are "high pressure" brass fittings which can get
> you into the 1600-2300psi range, but even at 2300psi, I still
> wouldn't use them on a vehicle - I'd like a larger safety margin
> than that.
>
>
> --
> -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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