Originally Posted by Matt in SV
Can you post a picture of the faucet, Jan?
It might help to see and identify what "some type of cylinder assembly" is. I'm wondering if it's an in-line water pump?
A regular Hot/Cold faucet would work in your diagram with just a plug on the hot side. I believe all City Water connectors have a built-in check valve. The fancy ones add a built-in pressure reducer.
I have seen trailer set-ups where the City Water line was connected to the Hot side and the Tank/Pump line was connected to the Cold side.