The Ellenroad mill engine of 1892 was a triple expansion steam engine built by J&W McNaught of St. George's foundry, Rochdale. When the new ring mill was built, the triple expansion engine was converted to a twin tandem compound engine by removing the high pressure and intermediate pressure cylinders and installing two high pressure cylinders. The conversion was undertaken by Clayton Goodfellow & Co Ltd, Blackburn. the flywheel was increased in size from 43 grooves for 1.5/8" (41mm) ropes to 44 grooves to accept ropes of 1.7/8" (47.6mm) diameter. 58.5 revolutions per minute, the new engine could produce 2650 IHP (indicated horse power).
Steam first enters the smaller, high pressure cylinders being directed into the cylinders through Corliss valves. The rotative valves are operated by Craigs cut-off gear and controlled by the Whitehead governor. The governor adjusts the valve gear continuously to ensure just the right amount of steam is admitted to produce the desired power and speed. The flywheel weighs over 80 tonnes: about the same as nine double deck buses.
At the back of the low pressure cylinders there are cross-heads that
provide pivots for the great connecting rods to the cranks, and which also operate the air pumps that are situated below the engine room floor. These pumps remove the air, water and condensate produced when the river water is sprayed into the condensers to cool the steam and provide a vacuum. Each engine has one condenser and two air pumps. When operating, the air pumps can move up to 6000 gallons of water per minute.
The society volunteers maintain the engine in full working order.