What mechanism causes the MMR to supply air to the user upon inhalation?

The mechanism that causes the MMR (Medium Minute Respiratory) to supply air to the user upon inhalation is the diaphragm pressing down on the demand lever. This action is crucial for the operation of the SCBA system. When a user inhales, a negative pressure is created within the facepiece or mask. This negative pressure causes the diaphragm to flex downward, which, in turn, activates the demand valve by pressing down on the demand lever. As a result, air is allowed to flow from the high-pressure cylinder through the regulator and into the mask, providing the necessary oxygen for the user to breathe safely.

This mechanism is designed to be reactive and efficient, ensuring that air is delivered only when the user needs it, preventing unnecessary air escape during exhalation or when not in use. The demand valve only opens when a user inhales, allowing for precise control of airflow depending on the user's respiratory needs.

This understanding is crucial for effectively using and maintaining SCBA equipment, as it emphasizes the importance of the demand valve system in providing respiratory protection in hazardous environments.