Let’s start with the easy stuff.
The following are single words with no hyphen:
The following are hyphenated:
The following are two words when used as a verb, but a single word with no hyphen when used as a noun or adjective:
cut off (verb) cutoff (noun, adjective)
drill off (verb) drilloff (noun, adjective)
kick off (verb) kickoff (noun, adjective)
shut off (verb) shutoff (noun, adjective)
stand off (verb) standoff (noun, adjective)
Example: Turn the shutoff valve if you want to shut off the flow.
Here’s where it gets tricky: online and offline.
When something is started up, it is said to be brought on line (two words); when being turned off, it is said to be taken off line (again, two words). The exact verb can vary: put on line, moved off line, etc. If you can insert the word “the” in between (taken off the line) and it still makes sense, then use two words. In nearly all other instances, online and offline are adjectives used as single words.
Example: There is a new online training course available, but the laptop is offline at the moment.
Finally, is it pumpoff or pump-off? The SPE Style Guide prefers the single word, while Schlumberger uses the hyphen. So it would depend on where your piece will end up!