Double check valves.....can they restrict flow?

[Just_back_from_the_pub]

A friend of mine has two basins in two separate bathrooms mounted symetrically, back-to-back, on a stud partition wall. The flow rate to one sink through both hot and cold taps is fine but through the other both hot and cold supplies are very poor. The only difference is that the sink with the restricted supply has each of its pipes fitted with double check valves. Can these make any difference to the flowrate? Maybe they scale up after time. Thanks for any help.

 

[kaboom]

Valves on both hot and cold? Sure they're not pressure reducing valves? What sort of h & c supplies are they?

 

[Just_back_from_the_pub]

Valves on both hot and cold? Sure they're not pressure reducing valves? What sort of h & c supplies are they?

Actually, you could be quite right there as the basin with the weedy flowrate is one of those glass jobbies without an overflow. Perhaps then it is compulsory to fit PRVs in this case. I must say I couldn't work out as to why there would be DCV's in this position. Thanks for any advice.