ORIGINAL: causeitflies
There are two types of Festo check valves. One is a ''one way'' valve and the other only closes when you remove the tubing from one end. You need the first type but probably have the second.
To keep it simple in Festo product there's only one model of 'check' valve. It has an aluminum body. (SMC makes a plastic bodied check valve that's just as good IMO) The other valve you're referring to is a self closing union fitting. They are easy to mix up with each other since the symbols are quite similar. Basically if you want one-way flow all the time, and its a FESTO product, its gotta be an aluminum housing. On the other hand, if you want a fitting for a UAT fill port that closes as soon as you disconnect the fill line, its the plastic body self closing fitting.
The 4mm check valve's part number is: 153462 / H-QS-4
The 4mm self closing union fitting's part number is: 153439 / QSK-4
Both are available for a minimum hose diameter of 4mm according to the catalogues.
Kelly