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3.2.8. Pump assemblies
3.2.8.1.
Venturi Pumps
The ACM 150 monitor has two air-driven ducts (venturi pumps). One is the Bypass Venturi
Pump. It draws a constant airflow through the tubes and the sample valves. This flow is
only interrupted when the sample valve is energized, i.e., when the ACM is sampling that
area. When areas are not sampled, they flow to bypass. This assures that the sample
lines are continuously flowing and refreshed.
The second pump is the Gas Cell Venturi Pump. It draws spent samples out of the gas
cell during the Evacuation mode.
The advantages of the air-driven venturi pump are:
• no scheduled PM service because parts do not wear out.
• generates virtually no noise or heat.
Should the air supply be interrupted, a mechanical pump turns on and takes over
automatically.
Figure 11. Venturi Pump Assembly
The venturi pumps are installed on a mounting plate. The check valves allow the venturi
pumps and the mechanical Backup Exhaust Pump to be pneumatically coupled to
standard bypass and gas cell vacuum lines. This allows either one to provide the suction
to draw the flow—the mechanical pump switches on automatically when the venturi pumps
fail to deliver adequate vacuum. The check valves permit flow in one direction only,
preventing the pump from drawing on the idle pump.
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