Air in Water Pipes?

Well Plumber came back last night, first of all he tried a new slightly different valve, I can't find anything simular on the web, so can't post pictures,anyway it still went 'Clonk', so he fitted a 'Non return Valve' in a pipe that went to the sink as he thought it might me drawing air or water back from the tap in the sink, that seemed to make it quieter, so then he fitted one to the flow into the cistern, that didn't make much odds, so then he put the Torbeck type one from wickes in..No 'Clonk'..Not totally convinced it won't return, the next 24 hrs will tell.

Thoughts are, get a valve same as i originally had that had the thread gone on it (an old Ball valve) or an 'equilibrium valve'..any idea how much these are, I belive they are costly, but it will be worth it if it does the trick...

Any other thoughts?

Thanks Steve