What do we commonly call the dowty retarder "dead dowty retarder" mean

Dowty retarder is a kind of hydraulic speed regulating equipment used in hump marshalling yard that does not require external energy and any control equipment, and can automatically control the rolling speed of vehicles to realize the safe connection of rolling vehicles. 

However, in the actual use process of the dowty retarder, as the use time increases, a variety of failures often occur, causing the dowty retarder to fail. One of the faults is that they cannot be stepped down no matter how hard they are used, and they cannot slide freely, forming the so-called "dead dowty retarder".