check valves

[johnad]

can anyone tell me where to place check valves,
i will shortly be installing new plumbing throughout my house,
shower no bath, outside tap, etc, how many will i need to put in ?
whats the difference between single and double check valves ?
do they have any effect on water pressure ?
any help please.

 

[kevplumb]

single on tank fed double on the mains the clue is is the name

 

[Bahco]

You need to put doubles on mains fed taps etc that could back siphon water back into the mains if there is a drop in pressure.
Put one on your outside tap.

As long as you have an air gap between your taps and spillover level you will not need DCV s for them

 

[ChrisR]

Full answer is much longer and depends how your house is plumbed. Suggest you look in a library Water Regs book.
Yes they affect flow, if pressure is low use a bigger one (eg 22mm on a 15mm pipe).