Complex sentence: Each generating set had a bunker for 1,250 tonnes of coal, fed into it by a conveyor belt system built by E. N. Mackley & Co, Gateshead.
Split into simpler sentences: Each generating set had a bunker for 1,250 tonnes of coal, fed by a conveyor. This conveyor belt system was built by E. N. Mackley & Co, Gateshead.