A pressure regulating device for use with a breathing assistance and/or resuscitation apparatus, which conveys gases along a gases pathway to a patient, includes a mounting for connecting the pressure regulating device to a first outlet in fluid communication with the gases pathway. The mounting holds a valve member that selectively blocks, at least in part, the first outlet. A control member can be manipulated to adjust a property of the valve member. The valve member at least partially blocks the first outlet when the pressure of gases in the pathway is below a selected level, and allows at least a portion of the gases to flow out of the first outlet when the pressure of said gases is above the selected level. The property includes a selected level of pressure whereby manipulation of the control member adjusts the level of pressure between a maximum level and a minimum level.
