The miniature mask oxygen regulator, shown in a cutaway view in figure 4-12, is intended primarily for use in aircraft having a low-pressure LOX system and ejection seats. It is often referred to as a miniature mask-mounted regulator. Since it weighs only 2.3 ounces and measures approximately 2 5/ 8 inches in length and width, it is easily mounted on the oxygen mask or user's torso harness. It is designed so that

Figure 4-12.- Cutaway view of miniature oxygen regulator.

with an inlet pressure of40 t0 90 psi, it will deliver 100-percent oxygen automatically to the user between the altitudes of 0 and 50,000 feet. Oxygen at system pressure, warmed to a comfortable temperature, flows into the regulator inlet port to the demand valve diaphragm. A small passage from the inlet line sends this pressure to the backside of the diaphragm; thus, the demand valve diaphragm is pressure balanced except for the slight imbalance caused by an area advantage on the backside of the diaphragm, which provides a positive sealing force. The vacuum caused by inhalation causes the sensing diaphragm to tilt downward, pushing down the demand actuating paddle. As the paddle is forced downward, its base is lifted from a set, which seals a second passageway from the backside of the demand valve diaphragm. Raising the paddle base allows flOW from this area, which causes a pressure drop behind the demand valve diaphragm and allows inlet pressure to lift the diaphragm from its seat, and oxygen flow occurs. Safety pressure is obtained by the safety pressure spring, which deflects the sensing diaphragm, causing flow through the unit until the force created by mask pressure equals the force of the spring. This returns the sensing diaphragm to a balanced condition. Automatic pressure breathing is obtained by diverting a small volume bleed from the inlet passage to the aneroid chamber. This bleed is normally vented from the aneroid cavity past the area labeled "aneroid vent" (fig. 4-12). At the altitude at which pressure breathing is to begin, the lip of the aneroid comes in contact with the seat, closing off the aneroid vent and building up pressure, which reacts on the sensing diaphragm. The pressure lifts the sensing diaphragm, causing flow until the mask pressure exerts a force on the sensing diaphragm equal to the force exerted by pressure buildup in the aneroid chamber.

The relief valve on the unit acts as a pilot device to open the exhalation valve of the mask. This is done by isolating the pressure pickup of the exhalation valve with the tube in the outlet port of the unit, so that the exhalation valve is compensated only by the pressure sent to it by the exhalation valve pickup tube.