How should combination valve be sized?

[Christhescott]

Hi, my incoming mains pressure is 6.5bar. I have a reliance 3bar reducing 5bar relief inlet control similar to the one pictured below. I am just trying to figure out if the parts fitted are correct for my mains pressure? Can't seem to find any guidance online. I get a loud fog horn noise when taps are run or toilet flushed so trying to see what might be causing it.

Thanks for any help with this.

 

[Madrab]

It's not about whether it's correct for you mains pressure or not - it's whether it is suitable to protect the unvented HW cylinder or not.

If it's chattering then the spring may be getting tired and it needs to be serviced or replaced, they don't last for ever. Your qualified unvented cylinder service engineer will be able to advise you.