blow off

1. A blowing off steam, water, etc.; -- Also, adj. as, a blow-off cock or pipe.

2. An outburst of temper or excitement. [Colloq.]

1.  Vent one's strong feelings; see blow off steam.
2.  Disregard, ignore; evade something important. For example, If you blow off your homework, you're bound to run into trouble on the exam. [Slang; second half of 1900s]
3.  Overcome, defeat easily, as in With Rob pitching, we'll have no trouble blowing off the opposing team. [Slang; 1950s] Also see blow away, def. 2.
4.  Ignore, abandon, refuse to take part. For example, The college is blowing off our request for a new student center. [Slang; mid-1900s]

On a boiler, an outlet to permit the discharge of accumulated deposits from water.

a tank which receives discharge from a boiler blow-off

The verb has one meaning:

Meaning #1: come off due to an explosion or other strong force