Abstract: A workpiece to be treated, for example, an engine cylinder, is held vertically with a liquid-tight seal in a treatment device including a head which is fixed in the working plane of a work bench, and a counterhead supported from the work bench by a bracket which can be raised hydraulically. The device is selectively connectible, through control valves and circulation pumps, to reservoirs containing different treatment liquids. The liquids enter the cylinder in an ascending flow through the head in such a way as to avoid swirling movements. Preferably, several treatment devices are arranged to work in synchronism.