Veeco MS40 Operation And Maintenance Manual page 58

Direct Flow:
The Direct Flow mode is ideal for testing parts that have a leak rate
specification less than 6 x 10
clean, dry and cannot tolerate exposure to back streaming mechanical pump
oil vapors during testing. In this mode, the test object is directly connected
to the high vacuum section and therefore the mass spectrometer. This allows
for much higher sensitivity and ultra-clean testing in comparison with reverse
flow mode, but requires a much lower crossover pressure.
During Direct Flow mode testing, the fine valve and fore-line valves are
open. All other valves are closed. Crossover takes place when the test
port is at 500 millitorr or less (adjustable by the system operator). The
fine mode test leak range is from 10 x 10
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NOTE
Once the MS-40 has crossed over into its direct flow
mode, and needs to range upward, it will stay in this
mode until it reaches the top of the 10-5 range.
-10
std cc/sec, or when testing objects that are
-5
to 4 x 10
3-5
-11
std cc/sec.