Message text written by Randall Young
>I don't use a filter for my air tools, because they don't need one, and
I've
seen what comes out of the air hose even in the relatively dry climate I
live
in. The 'cheap' air filters at best take the air down to 100% humidity at
whatever temperature and pressure is inside the filter, which may be fine
for
painting, but leaves plenty of moisture in the air for conventional brake
fluid
to suck out, or to condense in the reservoir on a cold night. I've also
found
bits of air hose in the screens in my air tools (which is a sign the hose
is
ready to be replaced). You'll note that professional 'power bleeders'
always
use a diaphragm between the air source and the brake fluid.
<
Randall,
It is a little known fact that air under pressure has less water-holding
capacity than air at a lower air pressure. This is why there is a
condensate drain on your air compressor tank. This means that if you lower
the airline humidity to 100% at pressure the humidity level of the same air
when the pressure is lowered (eg: to atmospheric pressure) will be lower.
Now all this assumes that temperature does not vary and as we all know the
temperature in a pressurized air system will change each time the pressure
changes. We all know better than to touch the discharge line from the air
compressor least we get burned. When air pressure is reduced the
temperature will also drop. Of course the temperatures in a static system
will eventually seek out ambient and if the compressor is idle over night
the air in the tank will be at the same temperture as the air surrounding
the tank. The air in the tank will likely be at 100% humidity, as well.
Not because it has picked up extra water vapor, indeed there is liquid
water in the bottom of the tank which is the excess beyond what the air can
hold, but because of the reduced water holding capability.
A dynamic situation has compressed air flowing through pressure reducing
valves (regulators) and flow control valves and changing both pressure and
temperature. And the air velocity will pick up and carry any liquid water
that happens to be in or near the air stream. That being said, a simple
filter is not sufficient to seporate the odd droplets of water that are
picked up by the moving air when air moves through the system. A proper
air dryer system will have provisions to cool the warm, recently compressed
air and a reservoir for the water that is safely away from the turbulent
air flow. But this is not typical in a domestic situation.
There is a device on the market that uses air from one of the tires as a
source of pressure. And how did that air get in the tire? It got there
via an air compressor. OTOH the air has been static in the tire and has
reached ambient temperature (unless the car has been recently driven) and
any liquid water is resting in the bottom of the tire safely away from the
valve stem.
And in closing (yeah!) since the air is not mixed with the brake fluid
(hopefully) but meerly applied to the top surface of the fluid. This is
the same as the atmospheric pressure applied to the top surface the rest of
the year. And this air can and does reach 100% humidity.
Just my humble opinion.
Dave Massey
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