PKP classification system (Polish locomotive designation) is a system of assigning letters and numbers to series and individual locomotives used by the PKP - Polish national railroad operator.
The system was introduced for the steam stock by the Ministry of Railways on 3 November 1922, shortly after Poland regained her independence (1918) when the Polish railroads inherited a variety of German, Austrian and Russian steam locomotives, each with its own type convention.
After World War II a similar system was also adapted for diesel and electric locomotives.
Digits mark subsequent classes, and their ranges also carry additional information on construction features.
A tender numbered 22D23 can carry up to 22 m3 of water, has four axles, and its construction was approved in 1923.