4-1
SECTION IV
TROUBLESHOOTING
4-1
LEAKAGE
Analysis of general operational experience with diffusion pumps indicates that certain locations are
more prone to vacuum leaks. The following locations should be checked first if leakage is the sus-
pected cause of poor system performance.
1
Inlet and foreline connections
2
Drain and fill plugs
3
Other compression fittings, such as high-vacuum gauges in the system
4
Threaded connections, such as foreline gauge
4-2
OUTGASSING
High-vacuum systems, even without external leakage, can also exhibit high gas loads due to out-
gassing 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 capability
of the diffusion pump, the diffusion pump will not function and the pumping action will essentially be
performed by the mechanical backing pump.
To estimate the gas load, isolate the system from all pumps after evacuation and measure the rate of
pressure rise. The gas load created by the system can be estimated as:
V x
∆
P
Q = ______
∆
t
where: V is the isolated volume,
∆
P is the pressure rise, and
∆
t is the time period of measurement.
4-3
POOR PUMP OR SYSTEM PERFORMANCE
Before proceeding with a step-by-step troubleshooting program, check the performance and accu-
racy of the vacuum gauges used on the system.
Table 2 shows the most frequent faults, their probable causes, and specific repair actions required for
each.
Summary of Contents for VHS-6
Page 27: ...Replacement Parts 5 2 ...
Page 28: ...Replacement Parts 5 3 ...
