The final two locks at Croydon Common raised the canal to the contour, and because there was no natural source of water a steam pumping station was built at the foot of the locks to pump water up to the summit pound. In June 1830 a new pumping engine was installed on Croydon Common which was the first commercial installation of Samuel Brown's gas vacuum engine, and quite probably the first commercial internal combustion engine in the world. The economics of the gas engine were interesting as the gas it consumed was made by turning coal into coke. The value of the resulting coke and coal tar by-products of making the gas substantially exceeded the cost of the coal, ground rent, repairs etc, so the gas vacuum engine made a profit of over £100 a year before considering the useful work it was doing.