This triple expansion steam engine, built by Worth Mckenzies of Stockton, was installed at Hereford Water Works in 1895 and is said to be the oldest of its type still working. It is still in the Hereford Water Works Museum so it has not really moved location since it first ran. I understand it is powered up on special museum days. Triple expansion engines were the most common form of efficient steam engines. A very rough estimate of this engine suggests the power to be about 50hp.
Photographs and details courtesy of Fred Starr.