The six engines built by Kessler were trialled with a Kessler boiler. This had a pear-shaped cross section and could therefore be set lower down between the wheels. The same effect was also attempted on the machines from Hartmann by using two boilers: a lower boiler with a small diameter and a larger, upper boiler. After two boiler explosions occurred, all the engines were equipped with normal boilers. All the vehicles had a steam dome in the centre, and the overhanging outer firebox had a flat top on which there was a safety valve and a pump (Fahrpumpe) driven by the crossheads.
