Hi,  I have been trying to figure out the information available on
Duo-Art spill valves, referring to Mike Kitner's rebuilding guide and
the MMD Archives.  Both stress the importance of having it right.

Mike does say that grands should have rolled-up thick felt in the
hole, as do the Archives, but does not say what the upright should
have.  Are the spills the same?

The hole in my upright box is slot shaped, lined with a piece of thin
felt, and the outside cover has a thick piece of felt which appears as
if someone has coated the outside in glue (to reduce flow?).  Is this
correct, and which of these two felts is called the "muffler" felt?

Thanks,
Peter Coggins