(3) The Mark-2 servo is held in the inspiratory phase but locked out of
access to the breathing circuit. The controlled function can be reestablished ONLY by
pressing the reset pushbutton, which dumps the gas trapped between the Mark-2 servo
and the inspiratory-venturi switch to atmosphere. If a second lockout occurs after the
next inspiratory cycle, the controlled-inspiratory time may have exceeded the preset time
limit, inspiratory time may be longer than expiratory time, or component failure may have
occurred in the Mark 2, holding the unit in inspiration. Malfunction or omission in
assembly of the small duckbill-check valve between the outlet of the inspiratory-
interrupter switch and the inspiratory time-limit valve would also cause premature
lockout.
e. During the expiratory phase (figure 1-15), source gas flows through the
inspiratory-interrupter switch to power the jet of the expiratory venturi in the shuttle valve
and through the inspiratory time-limit control to load the space between the diaphragms
of the compound-lockout cartridge.
f. Exhaled gases flow through the bottom diaphragm of the shuttle valve to meet
pressure from the expiratory venturi jet, then flow to the bottom of the outflow-valve
diaphragm and out to the atmosphere.
g. The Mark-2 servo is in the expiratory phase and no opposing pressure is felt
on the outflow-valve diaphragm. The expiratory venturi allows exhaled gases to flow to
the atmosphere.
MD0355
1-19