Cash-out refi confused

[David Sray]

Hello BP nation!  I've been looking into cash out refinancing on a duplex we recently purchased and think I simply don't have enough equity in it to pull anything worthwhile out. Trying to make sure I understand the process properly and hoping folks can help. 

Is the primary way people are able to pull a down payment back out quickly based mostly on the property appraising for significantly more after you've done some work on it and rented it out? 

If I purchased a property for $155k and, say, it's worth $165k now. I can refi at 70% of appraised value on the $165k, which would be $115.5k.  What I pull out in cash is then the difference between that $115.5k and the actual equity I have in it?

This is probably completely simple, but I'm still confusing myself.