Hydraulic hoses, Stainless steel vs Rubber
>If this looks like yours, the hydraulic line is best made
> braided stainless steel AN or "aircraft" hose.
I suppose it's time to reiterate a few things about SS braided
(having worked with them industrially for more than a decade).
There's nothing inherently wrong with rubber-covered hoses,
depending upon the material type, they can be superior to SS
hoses--in both wear resistance and burst pressure. As well, contrary
popular opinion, SS hoses have an expansion rate that is inferior
some of the better rubber-coated hoses.
Typically, these hoses use a Teflon or other fluorocarbon liner
has very little mechanical strength and will balloon easily--that's
there is the necessity for the outer stainless steel braid. But,
Chinese finger puzzle, the braid is flexible, and the line will
under pressure until the braid locks.
My favorite story about this was from an engineer with whom
I worked who
was producing his own variant of the Zink Formula Vee race car.
thought the SS braided hose should be better, so he replaced
hose and line in the brake system with it. The brakes bled out
pedal felt okay, but on his first hard, high-speed braking on
the pedal went to the floor and he went sailing off into the
fence. Afterwards, the pedal felt fine. Tried again, and the
happened. Then, he decided to look up the rate of expansion under
pressure and calculated the volume change for all the line he'd
installed and it exceeded the stroke volume. (!) Went back to
standard VW rubber hoses and steel lines and all was well again.
The lesson then is to keep the distance short if using such
brakes and/or clutch.
The other issue is wear. One of the best materials to resist
is... yup, rubber. One of the worst... yup, SS braiding. The
very small diameter, so they're easily worn through. When that
the strength of the hose declines rapidly. It's very, very important
that such hoses be clipped in rubber-cushioned clips, especially
areas where there's a high vibration level--one of the hoses
against a metal surface or edge can wear through in no time at
seemingly low amplitudes of vibration. Where clipping is not
the hose should be wrapped in a hard nylon garter coil (these
available for most hose outside diameters) to keep the braiding
from contacting other surfaces.
Rubber hoses do have their problems--internal cracking can cause
to wick out along the reinforcing fabric. As many people on the
know, very old rubber lines can crack sufficiently internally
to form a
flap that can block the line or cause pressure not to bleed off
the pressure is released.
But, if one wants to be convinced that there are some very good
lines available, just drop by your local industrial supply house
to look through their Aeroquip industrial catalog and compare
various hose types.
As for the cost being lower than one can make up the hose one's
wonder about that. These lines are typically -3 or -4 SAE. In
at wholesale, the line and fittings are worth perhaps $8-12.
it's not something with which one has a fair amount of experience
assembling, I wouldn't recommend making your own lines--but,
that $46 is in labor, overhead and profit, not parts.
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