With all hydraulic motors of the vane and piston type that have an odd number of displacement chambers, the smaller and larger section will find themselves within the pressure range on an alternating basis during a revolution. The effective rate of torque will fluctuate in line with this, with an average emerging accordingly (relative delivery fluctuation).
This fluctuation is much more noticeable at slow rotation speeds. It then becomes possible to determine the lowest rotation speed at which the motor can still run effectively.