So you are talking about a cylinder and piston between 6" and 12" in diameter?
Yes, quite a bit of equipment already out there. I think mine may have some unique features if it works as planned. I was a little disappointed that the pvc inside bore is not quite as smooth as I had hoped. With the 12" bore it might be forgiving enough to use as is. I am starting with some rough numbers. For example, if 20# of weight will take no less than 5 seconds to go down with a closed orifice that might be enough seal to meet my needs if not I will have to go for tighter tolerance’s.