With an Ocean Reef and many other FFMs, when you inhale, the breathing gas doesn't come through the oral-nasal piece. Instead, it's actually drawn over the faceplate, then between the oral-nasal and your face, then to your nose and mouth. Only exhaled gas goes through the oral-nasal (on its way to the exhaust valve). This minimizes the risk of hypercapnia (excessive carbon dioxide), by having the inhaled gas take a different path than your exhalations. It also reduces fogging, by sucking the dry inhaled gas across the faceplate.
Keep those two things in mind when you work on your own FFM. Good luck!
Keep those two things in mind when you work on your own FFM. Good luck!
