In an infusion circuit (1), a peristaltic pump (7) displaced the infusion fluid along a line (3), sourcing it from a batch container (2). When a weight sensor (5) detects an emptying of the batch container (2), the pump is halted. If on stopping the pump the pressure measured by a sensor (6) operating in an expansion chamber (4) does not drop in excess of a predetermined threshold with respect to a non-empty container (2), a non-secure situation is signalled, due to an excessive quantity of air in the expansion chamber.