HELP! Where's the check valve?

[goodbuoy]

This is what my brake booster looks like. In my car, a hose is attached to the tube (look for the J-shaped metal tube) going to the engine. I just want to ask on where should I find the check valve with this type of booster..? I wanted to replace it because my brake gets very firm when my engine is off. I expect to have 2 or 3 normal brake push upon engine shutdown.



Thanks a lot for the help!