The ship had two compound steam engines manufactured by John Elder and company. Each had one high-pressure and two low-pressure cylinders connected to a crankshaft. The connecting rods were in diameter attached to bearings on the crankshaft. A hollow steel shaft drove each of the two screws at a maximum 75 rpm. There were two boiler rooms, one each end of the engine room. Each contained two and two boilers operating at 61 psi. Similar high pressure systems had been used on HMS Alexandra launched in 1875 and Temeraire in 1876, but they were a recent innovation and more economical than the previous low pressure engines. Gangs of stokers were continuously bringing coal from the bunkers to feed the fires. The ship had a further 39 smaller engines for various purposes including bilge pumps capable of shifting 300 tons of water per hour, pumps for cooling water through the steam condensers, fans to draw air through the ship through a system of ventilation ducts, steering gear, hydraulic pumps for the guns, air compressors, winches and for generating electricity. The engine room was noisy, wet, greasy, oily and steamy. It would be a normal occurrence for engines to leak steam and for bearings to run hot so that they had to be hosed down to keep them operating. All the essential equipment was contained within the armoured citadel.Padfield p. 86-87
