A medical fluid infusion system includes a pump system configured to deliver a fluid drug to a patient. The system includes a pump, such as a piston pump, for driving fluid to a patient. One or more pressure sensors are configured to measure and detect changes in fluid pressure in a fluid flow line of the infusion system. The changes in fluid pressure, when detected, can be an indication of proper or improper functioning of a valve system of the pump system of the fluid infusion system.