An apparatus, breathing equipment training device, and method for breathing equipment training. The apparatus includes a shell and a diaphragm. The shell includes a first opening and a second opening. The first opening is configured to be inserted into a breathing opening in a mask to form a connection with the breathing opening of the mask. The diaphragm is inside the shell and positioned about the second opening. The diaphragm is configured to impede airflow into the shell through the second opening. The first opening can be defined by a first ellipse insertable into the breathing opening of the mask. The second opening can be defined by a second ellipse through which airflow enters into the shell. A diameter of the second ellipse can be greater than a diameter of the first ellipse.