A volumetric pump comprising: i) a drive shaft; ii) a shaft drawing in rotation said drive shaft, said drawing shaft being coaxial with the drive shaft; one from between the drawing shaft and the drive shaft comprising a housing seating of an end of the other; internally of the housing seating, the drawing shaft and the drive shaft, comprising in combination a coupling; iii) a static support structure of the drive shaft comprising: - a support with respect to which the drive shaft can rotate; - neutralising means of the radial loads bearing on the drawing shaft and coinciding substantially with one or more sliding bearings devoid of rolling elements radially interposed between the drive shaft and the support; said one or more sliding bearings comprising at least a first sliding bearing; iv) at least one thrust bearing which axially abuts, directly or indirectly, a first portion of the drawing shaft in order to neutralise axial loads bearing on the drawing shaft; characterised in that said coupling enables transferring any radial loads from the drawing shaft to the drive shaft, since the drawing shaft does not comprise bearings to oppose said radial loads; said coupling enabling transfer of any radial loads from the drawing shaft to the drive shaft comprises transversal sections of the drawing shaft and the drive shaft which sections are complementarily shaped and fitted one in another; said drawing shaft and said drive shaft, internally of the housing seating, in addition to said coupling enabling transfer of any radial loads from the drawing shaft to the drive shaft, comprise in combination cogged transmission means of the drive torque from the drawing shaft to the drive shaft; the cogged transmission means act on a first part of the drive shaft and of the drawing shaft; the complementarily shaped sections for the transmission of radial loads act on a second part of the drive shaft and the drawing shaft, the second part of the drive shaft and the drawing shaft enabling centring of the drive shaft and of the drawing shaft. i) a drive shaft; ii) a shaft drawing in rotation said drive shaft, said drawing shaft being coaxial with the drive shaft; one from between the drawing shaft and the drive shaft comprising a housing seating of an end of the other; internally of the housing seating, the drawing shaft and the drive shaft, comprising in combination a coupling; iii) a static support structure of the drive shaft comprising: - a support with respect to which the drive shaft can rotate; - neutralising means of the radial loads bearing on the drawing shaft and coinciding substantially with one or more sliding bearings devoid of rolling elements radially interposed between the drive shaft and the support; said one or more sliding bearings comprising at least a first sliding bearing; - a support with respect to which the drive shaft can rotate; - neutralising means of the radial loads bearing on the drawing shaft and coinciding substantially with one or more sliding bearings devoid of rolling elements radially interposed between the drive shaft and the support; said one or more sliding bearings comprising at least a first sliding bearing; iv) at least one thrust bearing which axially abuts, directly or indirectly, a first portion of the drawing shaft in order to neutralise axial loads bearing on the drawing shaft;