When to use double check valves

[vinny8]

Helo

I am about to embark on changing the bathroom suite. Last changed about 20 years ago (yep avocados gota go). Am i right in thinking that double check valves are not required. I seemed to recall that they are needed when supplying an outside tap etc or when the supplies are unequal , ie Manins cold tank fed hot water. Am i on the right lines for a post retro suite

Thanks

 

[Bahco]

Assuming all mains fed, not needed for baths, sinks, or toilet (if part 2 or 3 ball valve) as they are all protected by a type A air gap.

Toilet is type B if I remember correctly.

 

[kevplumb]

educate me marra what is a part 3 ball valve

 

[Bahco]

Plastic one marra

 

[kevplumb]

wazuc