Description Features of the MDI CPR Micromask Replacement Valve:The CPR MICROMASK Replacement Valve with filter provides the ultimate in protection for both the rescuer and the patient. Placement of the filter above the one-way, non-rebreathing valve insures no fluids from the patient will degrade the function of the filter. Designed to offer maximum air flow, the MDI replacement valve is the finest available. Replacement Valve Compatible with all CPR Masks using standard 15 mm I.D. or 22 mm O.D. openings.