Ok, here goes. I had a customoner that put an excess of 15,000 hours on a unit in less than three years. Units under full maint. 24/7 type of operation. Lease units. Swap out bottles and go. Those units were worn out. The down time for these units was and still is very low. A twenty year old unit that is down not moving product is not producing revenue for the user is just so much scrap metal in the way. The replacement units usually have been up graded from the last time the units were replaced.