Originally Posted by cef2lion
From what I read on the Shurflo Revolution 4008. The internal bypass is to prevent pump cycling on low demand in place of the variable speed.
Thought so too, however reviewing the docs again looks like it has an adjustment for the bypass, perhaps mine was not adjusted right from the factory, that may have helped, I didn't know it was there.
However a bypass just let the pump freewheel some wasting energy and running more than it needs to. An expansion tank lets it run full blast charging the tank not wasting any work and should run cooler as well. Many times when using the sink real quick the pump doesn't even come on and is simply served from the expansion tank. Seems like a better setup with the only downside being the $30 cost of the tank.
I might go with a bigger pump later and look into the Aquajet variable speeds. Want to add an outside fresh rinse would be nice to have as much flow as possible for a sprayer.