Blowdown
Blowdown turns up in 2 fields: machine shop, boilers. Here is what it means to the people in each one.
Blowdown in machine shop
The act of cleaning a machine or workspace with compressed air.
A cleanup routine where a machinist uses compressed air to blast chips, dust, and coolant off a machine tool, fixture, or finished part. A thorough blowdown is usually required at the end of a shift or before a new setup to ensure mating surfaces are free of debris that could cause misalignment.
"Give the chuck a good blowdown before you load the next piece so the jaws seat properly."
Blowdown in boilers
Draining some boiler water on purpose to remove concentrated dissolved solids and settled sludge.
As steam leaves, dissolved solids stay behind and concentrate. Surface or continuous blowdown bleeds water from just below the waterline to hold total dissolved solids in range, while bottom blowdown opens valves at the lowest point in short bursts to dump sludge. Bottom blowdown lines carry a quick-opening valve next to the boiler and a slow-opening valve after it. Water columns, gauge glasses and low-water cutoffs get blown down too.
"Bottom blowdown on two, open the quick-opening first, then the slow one, a few seconds, and close them in reverse."