In a message dated 1/1/99 6:23:33 PM Eastern Standard Time, vafred@erols.com
writes:
> Listers, just finished wiring my new work shed, my question is for the
> piping for the air compressor, is plastic pipe O/K or do I need metal, if
> so, should it be galvanized or the black pipe ?? The run is going to be
> rather long for attempting to keep all the water out, 1 in line filter &
> 1 filter/regulator, total up & down configuration is about 20 feet. As
> usual you advice is valued.
Fred,
There are two types of plastic pipe available -- one for water and one for
compressed air. The compressed air type is a bit more expensive than the water
pipe, but well worth the extra. You get the ease of installation of plastic,
and the safety of iron or copper pipe. In the quantity you are going to be
using, the extra cost is not significant. Do NOT use the ordinary PVC water
pipe, as it can shatter when used for air.
Ordinary PVC, designed for water usage, can also shatter under certain
conditions when used for water as well, but there are two factors which
prevent this potential shattering from being a problem; one, the pipes are
almost always behind walls, and, most important, the nature of water as
compared to air. Water is non-compressible, so if you get a rupture, you get a
small squirt of water and the pressure is gone. With air, which is highly
compressible, when you get a rupture, a tremendous volume of compressed air is
released, which can be quite deadly. In our nuclear plants, we test low
pressure piping with water at pressures up to 2000 psi, with no danger
whatever, even when testing unknown systems. As I said, if there is a leak,
only a small squirt of water is released before the pressure drops to
atmospheric. It's an eerie feeling, standing next to a small pipeline, knowing
it is pressurized to 2000 psi, but it's perfectly safe. Using water, you can
pressurize a tank to 2000 psi and then drill a hole in it with no danger -
don't try that with air!
There are lots of folks who have been using plastic water pipes for compressed
air for years with no problems, but there are also adults who played in
traffic as a child without being run over by a car. Nevertheless, it's
dangerous to be playing in traffic, and it's dangerous to use plastic water
pipe for air.
Plastic is the easiest to install, with copper being the next easiest. Iron
pipe is the cheapest to buy, but is impossible to install without special
tools -- pipe cutter, threader, etc. If you have to rent these tools, or pay
someone else to do it, the cost of iron pipe goes way up. Iron pipe will rust
with time and have to be replaced, but with air usage instead of water, the
time to replacement will be quite a bit longer (the air will have water in it,
which will settle in the pipe). Compared to our life span, copper is forever.
I don't know the life expectancy of plastic.
When the air leaves your compressor, it will be hot and have a lot of moisture
in it. As the air cools, the moisture will separate out and condense in the
pipes. For this reason, you want the pipes to be long enough for the air to
cool and for all the moisture to separate before the air gets to your tools,
and you want the moisture separator to be at the end of the air line -- you
don't want any more moisture separating out after the moisture separator. You
want to arrange the air lines so the moisture that condenses inside drains
away from the outlet, and provide a place to drain the line occasionally. When
you tap off the main line for your tool outlet, run the tap line vertically
for a couple of inches or so, then turn it down to the tool outlet. This
lessons the amount of water that gets to the tool. Air turns corners pretty
well, but water doesn't.
The few pipeline fittings you buy will cost more than the rest of the pipe put
together, but I recommend adding a few quick disconnects at various places in
the line, if your installation and tool usage locations allow it. My
compressor is in the garage, and I have a workshop just off the garage. In the
garage (two car), I have three outlets, and one in the workshop. I used the
special air service plastic pipe, btw. (Being an electrical type, I have two
control switches for my compressor -- one in the garage and one in the shop. I
have it arranged so that if I leave either one of the switches in the on
position, the compressor runs as usual, but if I turn the switch on and then
back off, the compressor will run just long enough to fill the tank. When the
tank is full, the pressure switch cuts off the compressor, and it won't start
again till I turn one of the switches back on. I have found that I often need
just a little bit of air for a project in the shop, and I got tired of
forgetting to turn off the compressor when I was finished, only to have it
cycle on and off for days as air leaks brought the pressure down while I
wasn't working in the garage. With four quick disconnects and two drain taps,
there is a bit of leakage.)
That's about all I know about it, hope it is of some help to you.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/index.html
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74
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