Hydraulic ram stroke monitoring apparatus

In a hydraulic arrangement comprising a hydraulic ram (1) and apparatus (3) for monitoring the working stroke of the hydraulic ram, such as for adjusting the cutting horizon of a mineral winning machine in the form of a coal plough or the like, the monitoring apparatus including an indicator having a housing (24) containing a tubular measuring chamber (25) connected to the hydraulic ram by a hydraulic line (2), the improvements comprising:

• the tubular measuring chamber being transparent on at least one side for the observation of the level of hydraulic fluid contained therein, means connecting the lower end of the tubular measuring chamber to the hydraulic line leading to the hydraulic ram, and an air-permeable but dust-impermeable plug (28) closing the upper end of the tubular measuring chamber, said plug thus establishing atmospheric communication with the upper interior of the measuring chamber while shielding the interior of the chamber from contaminating dust particles, and said plug being removable from the chamber to enable the insertion thereinto of a calibrating device.