On Jun 21, 12:48 am, Carl M wrote:

Have a filter the output of the tank, for sure. I have a thing
about rust inside a pressure vessel.

I -think- I've rust proofed several tanks by sloshing LPS-3 mixed with
kerosine around in them. A week hanging up in the sun dried out the
solvents. I did have to explain the bright red 60 gallon tank hanging
from a tree. (It's a bird feeder...)

There are several anti-rust chemicals that perform well. I've tried
LPS-3, Rustlick 631, and Sprayon 711. Boeshield T-9 may be better. MSC
had LPS-3 at a local store and I bought a few gallons.

The evidence that it works is no discoloration of the condensate from
the air tanks and no rust, odor or oil sheen on the water from the
solar heater, which had rusted through. I re-treated an air compressor
when a little rust started to show after 20 years.

The big stationary tanks are easier to drain if you connect a short
air hose whip to the drain fitting to bring the valve out where it's
accessible. It's easier if you can crack open the drain valve with one
hand and restrain the clear container with the other. Once the water
is gone you'll get a blast of air.

Simplified chemistry lesson:
If a gas is much warmer than its boiling point, air for example,
Pressure X Volume / Temperature = a constant. PV/T=nR. Double the
(absolute) temperature and the (absolute, not gauge) pressure will
double. Let it expand to twice the volume and its pressure and
temperature will drop. After it warms back up the pressure will be
half what it was before.

If it's near or below its boiling point, like water, the vapor
pressure depends only on temperature. When you try to compress water
vapor it simply condenses (less simply, it also warms up). The air in
the tank has as much water vapor in it as saturated outside air at the
same temperature, the rest is liquid. If the tank warms up some liquid
will evaporate, if it cools some vapor will condense.

When the compressed air passes through a regulator its pressure drops,
it cools and its volume increases. The water vapor that was at 100%
relative humidity now expands into the larger volume and the relative
humidity decreases, unless there is liquid water in the line. This
means that the easy way to dry compressed air is to increase the tank
pressure and let it expand more to the regulated output pressure.

Carl, if you cool the air to a little above room temp in the
evaporator core before it enters the tank, some of the water will
condense but you will still have air saturated with water vapor going
into the tank, and a little water will still condense in the tank as
the air cools the rest of the way. The evaporator would remove much
more water if it was in a bucket of ice water or a refrigerator. I
don't know if you can take out enough to keep the tank dry but it's
easy to try and a good excuse for an extra beer cooler.

I don't want the bother and expense of drying air to mainly run air
tools, so I use a STA-DRI in-line dessicator for painting and plasma
cutting and dry the calcium chloride out in a vacuum oven when it
turns color.

Jim Wilkins