Pump cassettes, infusion systems, and methods are described. An example infusion pump system may include a cassette recess with one or more valve actuators that extend through a surface of the cassette recess to operate a corresponding valve in a fluid passageway of a pump cassette mounted in the cassette recess. The valve actuator may include a base portion, a shaft extending from the base portion through the surface, and a spring disposed on the shaft and extending along a portion of the shaft. The spring may be disposed interior to the back surface. The system may include first and second valve actuators configured to operate corresponding first and second valves located on opposing sides of a pump chamber of the fluid passageway. A piston may be configured to cooperate with the first and second valve actuators to pump a fluid through the fluid passageway.
