Water system design

[Scott in Michigan]

Once again, a new owner question. My wife and I have a Cougar 32 RLI.

I'ld like to talk tech for a moment about the onboard fresh water tank and pump. I gather that a couple of the gentlemen on this board have some fair degree of technical expertise.

We can turn on a faucet and run it for a period of time before the pump kicks on. The water continued longer than what I would have expected from residual pressure in the piping. Is PEX tubing elastic enough that it acts like a pressure bladder in the system?

Also, is there a check valve in the discharge of the pump to isolate it when on city water?

Thanks, from Scott & Gin