Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Yes, there are two check balls - one in the center with its important spring providing back pressure (but not a lot). The one in the lower tube, below the center that screws into the tank, should move easily up/down.

It is really odd your problem... something has gone sideways I think inside the upper tube.  I hope you sort it out, as I'd be going crazy tying to figure it out.

Edit: revised check sum/spring/etc information.