The ships triple expansion engine viewed from above. In this type of engine, steam from the boiler was first admitted to the high pressure cylinder. This is the smallest cylinder, which in the picture is furthest from the camera. After passing through this cylinder the steam had lost pressure (but not to the extent of being at zero pressure), & gained volume. To use the remaining energy, the steam passed in turn to the intermediate pressure, then the low pressure cylinders. These being of progressively larger diameter & volume, to continue to use the steam at lower pressures & increased volumes.