Apparatus for infusing fluid

A system for pumping comprising:

• a plunger configured to move toward and away from a tube;
• a biasing member configured to provide a dynamically adjustable force urging the plunger toward the tube, the dynamically adjustable force varying based on operational conditions;
• an actuator configured to cause the plunger to move relative to the tube, the actuator being configured to mechanically disengage from the plunger;
• an inlet valve;
• an outlet valve;
• and
• a processor configured for:
• receiving a sensed position of a plunger relative to a tube;
• estimating a fluid flow within the tube based on the sensed position;
• and
• detecting an anomaly based on the sensed position of the plunger when at least one of the inlet valve and the outlet valve are in an occluding position and the actuator is mechanically disengaged from the tube while the biasing member urges the plunger toward the tube, wherein the anomaly is detected when a force applied to the plunger does not produce an expected displacement.