By 1897, additional pumping capacity was needed, and four extra pumps operated by triple-expansion steam engines were installed in an extension, designed to fit in with Bazalgette's main engine house, to the north of the older building. Later, in 1899, a further increase in London's population necessitated an increase in the efficiency of the original Watt engines, and considerable alteration to their design was carried out by Goodfellow & Co of Hyde, Manchester, for London County Council. They were converted from simple to compound engines with the original single cylinders were augmented by high and intermediate pressure cylinders. The additional steam required was provided by replacing the earlier Cornish boilers by more efficient Lancashire boilers with double flues and in 1901 the improved engines were fully working.