Stage 2/3/4 Clearance

Hah. Like I said, a lil' bit of debating spirit instilled and time. I'm through 2nd, 3rd and 4th stage. Still have no clue what the hell am I talking about?

Your hint:

I administer pressurised liquid around my line, only to halt something when triggered;

I am something you can sit on, tho you are my engine;

I could be used to generate electricity, and people do use me for numerous get around benefits.

I think I gave you too much hints. So start guessing!