Section 2
General Description
Cylinder Pressure
Gauges
Each cylinder gas circuit has a cylinder pressure gauge, located at the
bottom of the flowmeter panel on the front of the machine (see the
Flowmeter and Pressure Gauge Assembly figure earlier in this section.)
Each gauge is labeled and color-coded for its respective gas. When a
cylinder’s valve is open, its pressure gauge indicates the gas pressure in
the cylinder. The dial is marked with concentric scales for psi and kPa.
If two reserve cylinders of the same gas are open at the same time, the
gauge indicates the pressure in the cylinder having the higher pressure.
For nonliquefied gases (oxygen, air, oxygen-helium), the indicated
pressure is proportional to the gas content of the cylinder. For liquefied
gases (nitrous oxide, carbon dioxide), the gauge indicates the vapor
pressure of the liquefied gas in the cylinder. This pressure remains
constant until all of the liquid in the cylinder has vaporized. When the
liquid has vaporized, the cylinder pressure decreases proportionally as
gas is removed from the cylinder.
Oxygen Failure
Protection Device
(OFPD)
An oxygen failure protection device (OFPD) is a pneumatically operated
valve that protects the patient in the event of partial or complete loss of
oxygen pressure. Each gas circuit in the anesthesia machine, except the
oxygen circuit, is controlled by one of these valves. These valves, in turn,
are controlled by the gas pressure in the oxygen supply line. When
oxygen pressure is adequate, the valves remain open for an unrestricted
gas flow. Loss of oxgyen pressure causes the valves to close to a degree
that is proportional to the loss. The result is a restriction or shut down
of the flow of all gases except oxygen.
Reductions of gas flow are indicated on the flowmeters. In addition, if
the oxygen supply pressure drops below approximately 37 psi, an oxygen
supply pressure alarm is activated, causing the following events to occur:
• The Caution message LO O
2
SUPPLY appears on the central
alarm display.
• The red O
2
SUPPLY PRESSURE indicator on the main switch
panel lights.
• An intermittent audible alarm sounds.
• A 7-second whistle may sound, depending on the machine’s
configuration.
NOTE: When one source of oxygen pressure (either pipeline or
reserve cylinders) fails, but the other source is able to
maintain proper pressure within the machine’s oxygen supply
lines, the oxygen supply pressure alarm is not activated.
2-5
To Next Page
Loading...
