I was vacuuming leaves the other day when the "6.5 hp" Harbor Freight-powered vac let out a terrible bam-bam-bam... and started slowing quickly. Quickly shut off and locked tight. Oh, crap! Up to my ass in leaves and a broken vac!
It had to be the engine, of course, but when I got it in the shop, I found this:
When the blade failed, its backing plate bent and the blade tip started hitting bolt heads in the case. All the blades had real cracks - one is circled - and were not far from failure. I can think of no other reason than centrifugal force. The blades are about 3/16" thick - pretty surprising that they would crack like that.
Now, here's the best part: I had a spare impeller in the shed! Who keeps spare impellers? Impellers don't fail, why would anyone have a spare? You're looking at him, as they say.
Fixed in a flash and back to the leaves. Very satisfying.