© Edwards Limited 2008. All rights reserved.
Page 29
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Maintenance
B722-20-880 Issue D
Ultimate pressure cannot be
reached.
Is the pressure limited by water
vapour ?
Bake the system and pump.
Are any of the vacuum gauges
contaminated ?
If so clean or replace them.
Is the pumping speed insufficient
(due to poor conductance between
the pump and the gauge or too large
a chamber) ?
Increase the conductance or reduce
the volume.
Is the interstage inlet pressure > 0.5
mbar (50 Pa) (for the EXT70Hi 24V)
or
>
0.2 mbar (20 Pa) (for the
EXT255Hi 24V) ?
If the interstage inlet pressure is too
high inlet pressure at the
turbomolecular inlet is reduced;
ensure that the interstage inlet
pressure is
<
0.5 mbar (50 Pa) or
<
0.2 mbar (20 Pa) as appropriate.
Is the backing pressure > 10 mbar
(1 x 10
3
Pa) for the EXT70H/Hi 24V,
or > 5 mbar (5 x 10
2
Pa) for the
EXT255H/Hi 24 V ?
If so, the backing pressure is too
high. Check for backing pipeline
leaks. If the throughput is high you
may need a larger backing-pump.
Is the high-vacuum area of the
system contaminated ?
If so clean the high-vacuum system.
Check the rest of your system for
leaks and contamination.
If found clean the contaminated
areas and repair the leaks.
Remove the pump from the system
and test the ultimate pressure of the
pump alone (see
for
specification).
If poor check the pump for
contamination and if necessary
return the pump as described in
Section 5.4. Leak-check the pump. If
the leak rate > 1 x 10
-7
mbar l s
-1
(1 x 10
-5
Pa l s
-1
) consult Edwards or
your supplier.
The EXT is very noisy or there is
excessive vibration or both.
Is the pump rotational speed the
same as the resonant frequency of
the attached system ?
If so change the natural frequency of
your system or isolate the pump
using flexible bellows.
Is the vibration being transmitted
from the rotary pump ?
If so fit flexible bellows or a
vibration isolator in the backing line.
Is the noise irregular and getting
progressively worse ?
If so a bearing is defective. Consult
Edwards or your supplier.
Is the EXT making a constant high-
pitched noise ?
If so the rotor is out of balance.
Consult Edwards or your supplier.
None of the above.
-
Consult Edwards or your supplier.
Table 5 - Fault finding (continued)
Symptom
Check
Action
