2. The reduction chamber incorporates the
With the emergency pressure control lever in the
first-stage relief valve assembly (4) to protect the
EMERGENCY position, the regulator delivers positive
regulator against overpressures.
oxygen pressure to the outlet at altitudes when positive
pressure is not automatically delivered. In the TEST
3. The demand valve assembly (5) is opened
MASK position, oxygen is delivered to the mask under
when the pressure across demand outer diaphragm (6)
pressure too high to breathe and is used for checking the
forces the demand valve lever assembly (7) down. The
fit of the mask. The switch must be in the NORMAL
pressure differential exists during the inhalation cycle
position for normal system operation.
of the user by creating a reduction in the pressure outlet
(8).
Refer to figure 7-16 for the operation of an MD
type regulator.
4. Reduction in pressure at the pressure outlet is
sensed in the demand diaphragm chamber (9) through
1. Supply oxygen entering through the oxygen
the sensing port (10).
inlet (1) is filtered and passes through the manifold inlet
assembly into the inlet supply valve (2) and then into
5. During periods of flow, the oxygen passes
the first-stage reduction chamber (3) by action of the
through the venturi assembly (11). At the venturi
inlet supply valve control lever (24). The pressure of the
assembly, the flow of oxygen mixes with ambient air,
flowing oxygen is registered on the oxygen supply
which enters the regulator through the inlet ports (12).
pressure gauge.
18. CONTROL LEVER
10. SENSING PORT
1. INLET
19. ANEROID
11. VENTURI ASSEMBLY
2. INLET SUPPLY VALVE
20. DIAPHRAGM
12. INLET PORT
3. REDUCTION CHAMBER
21. PRESSURE BREATHER VALVE
13. DILUTER CONTROL LEVER
4. RELIEF VALVE
22. PLATE ASSEMBLY
14. DILUTER ANEROID
5. DEMAND VALVE
23. RELIEF VALVE
15. CHECK VALVE
6. DIAPHRAGM
24. SUPPLY VALVE CONTROL LEVER
16. EMERGENCY PRESSURE
7. DEMAND VALVE LEVER
CONTROL LEVER
8. OUTLET
17. TEST SPRING
9. DEMAND DIAPHRAGM CHAMBER
Figure 7-16.--MD regulator operational drawing.
7-16
