engine; steam indicator
Steam indicator engine made by Dobbie Mc Innes Ltd, 37 Bothwell Street, Glasgow. Engraved on the side is "Dobbie - McInnes" Patt A".
It is used to records "indicated horse power" The unit has a pressure connection direct to one cylinder of the engine. The cylindrical drum carries a paper sleeve and is connected by a cord to a reciprocating element on the same cylinder. The drum is controlled by a return spring and oscillates in synchronicity with the engine as the pen arm rises and falls in relationship with the cylinder pressure . The pen traces a PV diagram on the paper. Pressure on the y axis: volume or displacement on the X axis. The area under the graph indicates the work or power done by the cylinder.
The engineers rode in an indicator shelter constructed round the smoke box and front running plate in order to take indicator diagrams.
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