How this didn't end in mayhem I don't know... NAPA 2.25 ton floorjack, always been a great workhorse, just wandering around the garage stretching and for no reason decided to step on the lifting puck... and it sank about a half-inch, and stopped with a 'clunk'.
A step on it a few times looking at various bits and I see the solid metal box at the rear that forms the tank and takes all the force from the bottom of the bottle jack cylinder 'pops out' from behind the welded metal plate that actually transmits the force to the side plates.
Thought it was welded together, turns out there is a big bolt that's loose, completly invisible from above as it's tucked under the top if the caster mount. It let the side plate move away from the tank, allowing the tank to pop out from behind the backstop.
I've had this jack up on the bench to fix the little gear that operates the valve, have never even seen this bolt before.
Easy fix, but had that bolt backed out sufficiently, a jacking operation down the line would have been far too interesting.
Just had the engine cross member 3 feet in the air a month ago with this jack...