in fig3 at all times during use of the pump the pressure applied to the shafts 23 24 by the check pins 29 30 is such that the gears 13 14 are in turn thrust axially onto the front bushing set 15 a as indicated by arrow s u2032 u2033 consequently the axial forces s u2032 s u2033 and s u2032 u2033 which are produced during the operation of the pump all act in the same direction and contribute to keeping the gears 13 14 and the front bushing set 15 a and rear bushing set 15 b as a whole in abutment with the reference plane indicated by line vi u2014 vi in fig3 which is constituted by the face of the front cover 11 that is directed towards the inside of the shell 10 in this manner there is obtained a taking up of the axial clearances which is complete and constantly defined in spite of the oscillation of the axial forces produced during the rotation and the meshing of the gears 13 14 as is visible in fig3 the check pins 29 30 have different diameters in order to apply different axial loads to the two gears 13 14 this is because in the example of the figure the driving gear 13 and driven gear 14 are of a helical type and therefore during operation produce per se axial loads whose direction is counter to and in accordance with the.