Dear MMD,  I was hoping someone may help me with a small question.
I am having a go at making my own singing bird.  I am using some
drawings to guide me along but have a question about a certain part.
Unfortunately I live in a singing bird cultural backwater and am unable
to get to see one in the flesh, so here is my question.

There is a rod which gets tapped to set off the whistle.  It penetrates
a small pressure box and moves a valve.  What stops air moving out the
hole where the rod goes in?  Is it just a good fit?  Is the movement so
fast that it is neither here nor there?  Or does it use a floppy leather
seal to allow movement but not penetration of the rod into the chamber?

I hope this question is in the realm of MMD.

Thanking you in advance,
John Hutchison