RE: Robart check valve failures
The name of FESTO's non-return valve is H-QS-4, for the 4mm one.
[link]http://catalog.festo.com/enu/asp/DefaultPSresult.asp?ID=153462&L=001[/link]
Clippard also has one, but this is the "screw on" type. Works as good as the FESTO but larger.
Brg Thomas