Abstract: A pneumatic metering unit, which operates with vacuum pressure to dispense monograin seeds. Particularly, the pneumatic dispenser subject matter of the invention operates with low applied torque, while maintaining tightness in the vacuum chamber and keeping the working pressure constant, without variations or fluctuations due to the action of the seal, beyond the normal variations, due to the nature of the work, within the operating pressure threshold. In this sense, the reduction of necessary moving parts that could suffer jamming, as well as the implementation of an axial action spring that holds the seal in contact with the dosing plate in a constant way, regardless of the conditions and material characteristics of the seal, stand out.