check me check valves (double)

[darren7]

could someone please explane the correct lcation of double check valves?

I have been plumbing up to my sink, in the kitchen. I have had a look at a few installations and they do vary, I understand that the valve is to protect contamination.

I have seen the valve fitted just after the stopcock in one persons house, and on another I have seen one just fitted where the main tee of to the boiler.

1,what is the correct location for a double check valve, and can you have more than 1 in line.

2, why a single check valve

thanks Darren

 

[Bahco]

Double check valves are used where there is a chance of water back siphoning into the mains i.e. outside taps or showers where the head can be submerged into the water etc.
If you fit valve just before the appliance you should be alright.
Single check are used in low pressure pipes such as cistern fed.
My personal view is that 1 double check is sufficient protection for the whole house fitted just after the incoming mains stoptap as no water could be drawn back into the water mains.
What does anybody else think (I know the regs tell us otherwise)