[dusted]

When you compress air, the moisture falls out, the amount that falls out depends on pressure and temperature. pretty much all normal compressors simply have a, I don't know the right english word, but.. a valve at the bottom and once in a while (like, once a year or less, depending how much you use it) you take the pressure mostly off the compressor and open this, then the water is blown out.

[extrapickles]

Fancy air compression systems (eg: not consumer) will have a drain valve that automatically opens when the pressure falls from turning system off for night/weekend/other maintenance so people don't forget to drain it.

Its also not just water that is collected at the bottom of the air tank, compressor oil also collects. Oil can also be deliberately added by either as a byproduct of compressor design or from separate equipment, into the airstream help lubricate and protect equipment from the moisture, reducing the need to remove the moisture through other means.

[aj7]

About the only thing practical thing that valve does is perhaps lengthen the time fir the tank to rust out. Any serious industrial installation winds up with a refrigerated water removal unit.

[extrapickles]

It also helps keep a slug of water from entering the air lines if employees (and management) puts off draining the accumulated water for too long. You can also get ones that are triggered by a float if the system is for 24/7 operation.

[TheSpiceIsLife]

Any serious industrial installation will have multiple mitigation approaches.

[TheSpiceIsLife]

Ours are on a timer to blow off a small amount of air at a few low spots in the system every five minutes, even though having a refrigeratant type demudifier.

One of the devices stopped working between services and the bottom reciever tank half filled with water.

Edit: they're call bleed valves