Why do you swap out the valves? Have you had issues in the past?
Valves don't last forever and need to either be rebuilt or replaced. Logic says just have them rebuilt at hydro, which is a strong recommendation of most knowledgeable folks. Every 5 years is a good rule of thumb. However, when I looked at the economics of the cost of a valve rebuild (parts and labor) vs. a new valve (when you shop in advance and buy them when they are a good price), the cost comes out to be about the same. I therefore typically choose to go with a brand new valve at hydro.