Stuart Model 1-A Vertical Steam Engine

I did not build this Stuart model steam engine. A friend of mine built it. He done a remarkable job and paid special attention to every detail of its construction. It stands approx. 15" tall and is mostly made from cast iron.
It has been run on steam, but not by me. I only ran it on compressed air. It runs on as low as 3 PSI. of air. the only problem that I found is a slight knock in its operation. As of yet, I have not been able to track this problem out yet.... But I will.