Based on the structural dynamics and hydrodynamic lubrication theory

a kinetic model of plunger and barrel assembly was established

and the micro motion characteristics of plunger offset and inclination were calculated. Moreover

the influences of the three key parameters of maximum lift

initial sealing length as well as initial clearance between the plunger and barrel on the micro motion of plunger were deeply investigated

and an improved model design was proposed. The calculation results show that when increasing the maximum lift

the plunger offset increases

but the inclination decreases. In addition

the proper increase of the initial sealing length and decrease of the initial clearance between the plunger and barrel leads to the reduction of the plunger offset and inclination

which improves the micro motion of the plunger. In the improved model

the maximum plunger offset and inclination can be reduced by half.