How does a water pressure reducer fail?

Hi Mike and welcome to The Plumbing Page on AMHD.
You piggybacked on a 4 year old dead thread so I gave you one of your own. Before you post look in the upper left hand corner for the date..

How does a water pressure reducer fail? PRV valves (see image) could allow too much pressure to enter your system. It would really help if you listed your complaint. Back to you. Tom