In 1992, I self-published a thick book I called, "The Lost Art of Steam Heating." I did this because I could not get a publisher interested in something that few, if any, contractors had installed since the 1930s. I thought it would do well in New York City, where there are still plenty of steam-heated buildings, but to my delight, we sold tens of thousands of copies everywhere, and even in Hawaii. Go figure.
A chapter in that book dealt with the causes of water hammer, which will plague any system that suffers from neglect. Water hammer happens when water hangs around inside the pipes long after the other party guests, those being air and steam, have left. The water lies in the horizontal pipes because of poor pitch, and the next time the steam arrives, moving at about 60 mph, it rams the water down the pipe like an artillery shell. The water, which for our purposes is not compressible, hits the first turn in the pipe with a wallop that sounds like someone is hitting an anvil with a sledge hammer. Hence, the anvil chorus, but minus Giuseppe Verdi’s operatic talents.