Friction assessment plunger to barrel of sucker rod pump in design rod string

The article considers the influence of friction forces on the durability of sucker rod string. Considered dry and viscous friction of plunger to barrel, and the influence of hydrodynamic forces arising from the movement of the plunger in the liquid in the annular gap plunger assembly. There are the influence of these frictional forces on the amplitude component in the calculation of the above stresses. It is shown that in spite of the lower amplitude of the relaxation oscillations, they also have a negative impact on the durability of rod string due to their high frequency.