Pumping units are used to supply fire-fighting systems (automatic and with hydrants). The stations are equipped with a compensation pump, which serves to maintain pressure in the system without turning on the main pumps. They are activated when the pressure in the fire-fighting system drops. The compensation pump is the first to be activated; if this pump is unable to restore the pressure, the feed pump is activated. When there are several feed pumps in a station, they are activated in cascade.