A metering mechanism including a metering element that is translatably mounted in a jacket, the jacket being mounted in an adjusting sleeve that can cooperate with the jacket by way of a screwing movement, the screwing/unscrewing movement causing a translatory movement of the metering element; at one end, the metering element is provided with a check valve, and at the other end, same accommodates a plunger, the reciprocating translatory movement of which creates suction at the end of the element provided with the valve, followed by expulsion into a volume surrounding the other end of the metering element via a passage formed in at least one first sealing device and in a second sealing device. A proportioning pump including a metering mechanism of the type as well as to a method for using a pump of the type in at least two metering ranges.