air compressor safety (comprised, in the main, of "DRAIN THAT THANG!")

 Here's the thing: compressed air stores a lot of energy. Like, a LOT of energy. So much so, it was once considered for powering pollution-free vehicles, and a few early experimenters who didn't understand gases too well even built some prototypes. As it turns out, compressed gases are lousy for practical energy storage because of the heating and cooling problems.  Nevertheless, a vessel containing compressed gas can do a LOT of damage...

 Stored energy that can release all at once is dangerous.

 Drain that thang!
  The reason compressed air tanks explode is nearly always corrosion, caused by inadequate drainage of the condensate which forms in the tank and is left there too long, rusting out the tank until it can't hold pressure any more.  Manufacturers provide a drain valve on the bottom, and recommendations for how often to drain it vary from daily to monthly, depending on frequency of usage / operation.

Your safety valve won't save you.
  Air compressors come with a safety valve which is supposed to prevent over-pressurization of the tank in case something goes wrong with the pressure control switch.  Which is fine, but it doesn't open until the pressure exceeds the setting of the pressure switch by some significant margin.  And even at the normal operating pressure of the compressor, the stored energy in the tank is enough to kill or severely injure bystanders and blow holes in cement block walls if the tank were to explode for some reason...

 I got a scare when I realized I'd forgotten to drain my tank for a long time, and when I did, a lot of rusty water came out.  So I installed an automatic drain gadget. These things occasionally open the drain valve to let the water out, operated by one of two means: an electric solenoid valve controlled by a timer, or a pneumatic device triggered by the "unloader" of the compressor.

 Mine was of the latter type (it operates in a brief pulse every time the compressor shuts off, which seemed sensible and conservative) and it wasn't expensive.  It was also a cheap import.  And I trusted my life to it.

 Recently, I thought to check on how well it was really doing, and see if the tank needed draining (the manual drain stopcock was still there).  Out came a bunch of rusty water again.  Ugh.  The device was working, but the brief time it was open wasn't enough, and over time, condensate accumulated.

 So now I'm going to install a timer-operated device which will open every N minutes for N seconds - whatever I set it to.  This < $30 device seems like good insurance.  And maybe I'll put up a sign somewhere to remind myself to check it manually anyway.  I dislike the idea of a ticking time bomb in my shop, and compressors explode a lot more often than you might think - I did some searching, and it's disturbing how often they are in the news.

Why we don't use PVC pipe for compressed air
 I thought about including some gruesome pictures to sorta drive the point home here, but I decided this isn't that sort of blog.  PVC pipe is cheap, so occasionally someone who doesn't know any better decides to use it to distribute compressed air around the shop.  And they feel pretty good about themselves until age, oil vapors from the compressor, and UV light take their toll and the pipe explodes.  When PVC pipe explodes, it shatters into small jagged shards which become shrapnel.

Which pipe or tubing can be used safely?
 Nylon, polyethylene (but check the pressure rating!), copper, or "iron" (steel) pipe can all work because when they fail, they fail by splitting (due to their material properties) rather than shattering.

 There are some nice shop air line kits on the market which come with nylon tubing, push-to-connect connectors, and fancy mounts to attach quick-disconnect receptacles firmly to the wall.  They're also somewhat expensive, and the combo of connectors and tubing doesn't necessarily maintain a constant ID, as I am trying to do.

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Afterword
 Notes from the Amazon page for my shiny new auto drain valve, and I quote, verbatim:

2. Attention to the direction of the arrow when the valve body; outlet do not use the impact of the hose does not impact

4. The factory has been connected to the cable drain valve, fade for the fire line L, blue for the zero line N, yellow and green color for the safe ground GND
5. Always tighten the long screws on the terminal box to prevent the water from burning

Good show, fellas.  Really inspires confidence.