(2) Prevacuum high temperature steam sterilizer. Figure 3-4 is a diagram of
this type of sterilizer. The prevacuum steam sterilizer provides a more efficient and
faster method than the gravity-displacement sterilizer for the removal of air and the
injection of steam. This permits the processing of larger quantities of materials in a
short time. This sterilizer uses a vacuum pump and a steam injection system. The air
in the chamber is almost completely evacuated from the chamber by the vacuum pump.
The steam injector preconditions the load and helps eliminate the air from the
packages. When the sterilizing steam is admitted to the chamber, it penetrates to the
center of the packages almost instantaneously. Because of this rapid penetration,
higher temperature can be used and the time of the overall sterilization cycle can be
reduced. The cycle time for the prevacuum high-temperature steam sterilizer begins
when the sterilizer is started and runs through completion. External factors, the size
and type of load affect the cycle time with the prevacuum sterilizer. Exposure time for
the prevacuum type begins when the temperature reaches 270F (132C) and ends
when the temperature falls below 270F. The minimum exposure time for a prevacuum
high-temperature sterilizer is 4 minutes. The cycle time will be longer and will include
the removal of air by the vacuum pump, the heating period for the steam, the
penetration period for the steam and the exhaust and cooling period. The sterilization
cycle for prevacuum sterilizers is greatly reduced by the shorter penetration period,
higher temperature, and rapid exhaust and cooling time caused by the induced vacuum.
The holding and safety period (exposure time) is shortened by the increased
temperature. Local procedures for the operation of the prevacuum sterilizer should be
carefully followed.
Figure 3-4. Simplified diagram showing withdrawal of air from chamber,
using prevacuum and steam injection. American Sterilizer
Company, Erie, Pennsylvania.
MD0937
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