Labconco Type C1 Biosafety Cabinet Models 30468 - Manual (Page 31)

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Inlet Relief Valve
Also unique to the Axiom is the Inlet Relief Valve, The intake valve is angled
such that the incoming make-up (room) air must keep the valve open to
maintain normal operation; a loss of exhaust volume will allow gravity and
air pressure to close the inlet valve and open the magnetic switch, resulting
in an exhaust alarm.
Figure 1-8b
Intake Valve
Alarm Switch
Exhaust System
Key to the Axiom is its exhaust flexibility. When properly configured, the
HEPA-filtered exhaust can be recirculated back into the laboratory.
When configured for, and connected to an external exhaust system, the
airflow patterns are similar to the definition of a Type B1, however, the
integral exhaust blower and Inlet Relief Valve changes the operating
characteristics of the Axiom.
The CAP (Constant Airflow Profile)-programmed exhaust fan motor draws a
constant volume of air through the exhaust ductwork and exhaust HEPA
filter, and ‘presents’ the air to the exhaust system. This means the inflow
volume will remain constant as the exhaust system fluctuates, or as the
exhaust HEPA filter loads.
This arrangement lowers the vacuum required to operate the unit to a
constant 0.3 inches H
2
O; far lower than traditional Type B BSCs.
The inlet relief valve is pulled opened when the exhaust system draws more
air than the Axiom exhausts. If the exhaust system fails, gravity and positive
air pressure cause the Inlet Relief Valve to close, activating the sensor to
signal an exhaust alarm.