6" dial steam pressure gauge

6" dial steam pressure gauge made about 1860 (diaphragm type)

As boiler pressures increased, the mercury gauge originally used became very inconvenient, owing to the height of the column required, hence locomotives were unprovided with any means of telling the steam pressure; in a few instances a form of thermometric gauge was adopted, but the usual practice was to rely upon the indications derived from the spring-loaded safety valve. Mr. Sydney Smith, of Nottingham, was one of the earliest to produce a convenient form of mechanical pressure gauge, and this he patented in 1847, while in the same year he submitted it to George Stephenson, who at once had it tried on one of the boilers at his Tapton colliery.