A pressure regulating device (601) for a gas delivery apparatus (600), which conveys gases along a gases pathway to a patient, comprises: a mounting (613) having an inlet port (602) for receiving pressurised gases； an outlet port (604) for delivering said pressurised gases to a patient (119)； and a relief port for regulating the pressure of said gases； the relief port including a valve member (608) biased against a valve seat member (611) and arranged to open when the pressure of said gases exceeds a selected level in order to release some of the gases out through the relief port； wherein the position of the valve seat member (611) is manually adjustable within the relief port using a control member (622), in order to adjust the selected level of pressure at which the valve member (608) will open.
