 Not until the last ten did the boiler pressure rise to 160 lbf/in² (1.1 MPa), but in course of time all the engines of the class were fitted with 160 lbf/in² two-ring boilers.In 1889 one of Holden's shunting tanks engines was fitted with the Westinghouse brake and evaluated on passenger working.The 1889 experiment resulted in eighty of these tanks, slightly larger than Class T18 and classified as GER Class R24, being turned out from 1890 to 1896.