The pictures below were from a job I did for a nice gentleman in Gloucester. The bike had been his sons, but he had sadly passed away, and now his dad used it.

As you can see the rear tyre was flat because the valve had been ripped out of the tube.

When a tube is fitted there should be a nut both sides of the rim, i.e. one inside the tyre when fitted and one outside. This will clamp the valve firmly and relieve pressure where the valve meets the tube, so when tube moves around it wont rip it out.