A section of my central heating was badly designed so that return water from zone 2 can flow backwards through a radiator in zone 1.  I tried a double check valve but that made a lot of noise whenever water was being pumped through it.  So I moved on to a single check flap valve which is silent except when it closes; closure causes water hammer in some pipes buried in a wall.  I think the problem is that these pipes were not secured so move and bang against a beam.  I tried fitting a hammer arrestor (a flomasta bell-shaped type) but it only worked for a week.  

 

What I seem to need is a flap valve with a slow-close mechanism.  These appear to be used in North America for basement sump pumps but they are hard to come by here and anyway they don't look to be up to the standards required for central heating with pressurised water.  I can't find anything that seems to be appropriate for use in domestic plumbing.  Any suggestions?   

Are you saying you put a ‘swing check’ valve in?