The physical process where high-pressure, high-temperature water instantly boils into steam upon entering a lower-pressure environment. In steam systems, this happens constantly when condensate passes through a steam trap into the return piping. The resulting flash steam contains usable heat energy, which is often recovered in a flash tank to preheat makeup water or feed low-pressure loads.
The trap is blowing through, or we're just seeing a lot of flash off the high pressure drip leg.
Also heard as
- flash steam
Do not mix it up with
- Carryover: Flash is a phase change from pressure drop, while carryover is liquid water being physically dragged into the steam header.
Related terms
Steam trap
An automatic valve that drains condensate and air out of steam lines and equipment while holding steam back.
Condensate return
The piping and equipment that bring condensed steam back to the boiler room for reuse as feedwater.
Blowdown
Draining some boiler water on purpose to remove concentrated dissolved solids and settled sludge.