lsayre wrote:I've heard that each time a PRV opens it weakens it a bit. Is this generally true?
PS: I've heard the same for electrical breakers....
This is not true. Any safety device needs to be tested per manufacturer's recommendations. Some B&G relief valves I have purchased have a tag on them recommending a yearly opening via the lever. I assume this is to ensure that they do not stick closed as I have had valves do.
What you need to be concered about is that corrosion or sediment does not get under the seat.
Electrical breakers should be tested or flipped yearly also. Commercially, testing is available but it is not economical for residential size breakers.
However, using a circuit breaker as a switch will eventually weaken it if it is not rated for switching duty. For instance, a building where someone come in and turns on the lights with the circuit breaker would be a concern. Switching rated breakers are a must for this application. This is known as SWD rated.