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Technical Information
Troubleshooting
Leakage
If leakage is the suspected cause of poor system performance, first check the
following items:
Inlet and foreline connections
Drain and fill plugs
Other compression fittings, such as high-vacuum gauges in the system
Threaded connections, such as a foreline gauge.
Before proceeding with a program of step-by-step troubleshooting, check the
performance and accuracy of the vacuum gauges used on the system.
Outgassing
High-vacuum systems, even without external leakage, can have high gas loads due
to outgassing from internal surfaces or processes. The pressure in the system is a
result of gas load divided by pumping speed (p = Q/S). If the gas load Q exceeds the
maximum throughput capa- bility of the diffusion pump, the diffusion pump will not
function and the pumping action will essentially be due to the mechanical backing
pump.
To estimate the gas load, isolate the system from all pumps after evacuation and
measure the rate of pressure increase.
The gas load can be estimated from the following relationship:
where V is the isolated volume,
of measurement.
76
∆
P is the pressure rise, and
High Throughput Diffusion Pumps User Manual
∆
t is the time period
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