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Hi.  I was told you may know the answer.  I have a baby grand
reproducing player piano with the Simplex system.  The pump has
three air fittings.  The big one is for the draw, the mid-size one
is about 3/4-inch (I think it's for the damper rail), but I don't
know what the small one is for.  It's about 1/4 inch in size.

Thank you, Phil