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.
4-17
