A dilation catheter system is provided to dilate the ostium of a paranasal sinus or some other anatomical passageway (e.g., within the ear, nose, or throat, etc.). The system may include a dilation catheter, a dilator, a guide catheter, and an inflator. The dilation catheter may be positioned between the dilator and the inflator. The guide catheter is configured to guide the dilator into the affected passageway. The inflator may then be actuated to transfer fluid from the inflator, through the dilation catheter, and into the dilator. The transfer of fluid may inflate the dilator to an expanded state to open or dilate the affected passageway. The inflator may include a body, a plunger assembly, and locking features that selectively secure the position of the plunger assembly relative to the body by moving along a path that is transverse to a longitudinal axis defined by the plunger assembly.