A chemical or chemical compound (L) is supplied via at least two displacement pumps (1, 4) to a common supply line (11), through which the chemical or chemical compound (L) is supplied to the operating device (12) of a fibrous web machine. Each pump (1, 4) has a corresponding electric actuator (2, 5) which is equipped with a corresponding control drive (3, 6). The fibrous web machine has a measuring device (8; 8a, 8b) for determining the phase angles of at least the first and second actuators (2,5). A control signal based on the determined phase angle information is formed and transmitted to the first control drive (3), based on the control signal, the difference between the first and second electric actuators (2, 5) is adjusted. An electric synchronization signal between the control drives (3, 6) maintains the difference between the phase angles electric actuators (2, 5).