A medical breathing apparatus incorporating a regulator for supplying breathing gas to a patient from an air hose 11. The regulator supplies breathing gas on demand to the patient via a mouthpiece or similar attached to an output connector 55. The connector forms part of a removable output unit 4 incorporating a filter 53 and an exhale flap valve 57/58 on the patient side of the filter. When the patient exhales, exhaled gas entering the connector 55 exits to atmosphere via the exhale valve without passing through the filter into the interior of the regulator, thus reducing cross-contamination between patients. Also described is an improved valve seat 16/valve member 18 assembly in which multiple spaced pivot points 22, 23 are defined to cause the mechanical advantage for operating the valve member to reduce as the valve opens, thus reducing the force needed to operate the valve at lower flow rates.
