Maintenance and Service 9-5
4. Disconnect the pressure transducer air tubes and plug the ends.
The pressure transducer must not be subjected to high vacuum
or high pressure.
5. Plug the inlet of the CPC. Connect a vacuum source to the exit
side of the HEPA filter. Connect a pressure gauge or manometer
to the vacuum as shown in Figure 9-3. Place a shut-off valve
between the vacuum pump and the pressure gauge.
Pressure Gauge
or Manometer
Valve
Vacuum Pump
HEPA Filter
Plug
Inlet
CPC
Figure 9-3
Checking for Leaks With a Vacuum
6. Draw at least 560 mm Hg [300 inches of water] vacuum through
the instrument and close the valve. Switch off the vacuum
pump.
7. Check that the CPC loses no more than 5.6 mm Hg [3 inches of
water] vacuum in a 10-minute period.
8. If you find that the CPC leaks, first tighten all fittings and screws
and repeat the vacuum test. To locate a small leak, replace the
vacuum source with a compressed air source as shown in
Figure 9-4. Introduce approximately 69 kPa [10 psig] into the
CPC. Search for leaks by squirting a soap-and-water solution
around fittings, O-ring seals and any other possible leak
locations. A leak shows up as numerous small bubbles in the
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