Question: On the hot water outlet there is a 1-way check valve. Can I do without this?
Answer: We don’t think you should remove something that was deemed necessary by the engineer that designed your fresh water system.
The 1-way check valve is there to prevent water back flowing into the tank. While you could remove it, the removal might cause other problems like hot water mixing with your cold water. We are not plumbers so this is largely speculation on our part. Others are invited to chime in on your question.