B756-50-880 Issue C
Page 18
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MAINTENANCE
Table 4 - Fault finding
Symptom
Check
Action
The pump does not reach 80% speed
on ramp-up.
Is the inlet pressure too high? Is the
backing pressure too high?
If so, reduce the pumping load, or
check for a gross leak into the
system.
Is the EXT70/70/200H pump running
too hot?
Increase the cooling air flow. Check
that external heat sources (such as
system bake out heaters) are not
excessive.
Does the rotor rotate freely?
If not, the EXT70/70/200H pump
bearings are damaged. Consult
Edwards or the supplier.
The pump speed reduces while the
pump is running.
Is the pressure too high?
If so, reduce the pumping load or
check for a gross leak into the
system.
Is the EXT pump running too hot?
Increase the cooling air flow.
Does the EXT pump rotor rotate
freely?
If not, the EXT70/70/200H pump
bearings are damaged. Consult
Edwards or the supplier.
The EXDC160 Controller phase LED's
do not go on.
-
Consult EXDC controller manual.
System operating 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 > 0.2
mbar (20 Pa)?
If the interstage inlet pressure is too
high, inlet pressure at the
turbomolecular inlet is reduced;
ensure that the interstage inlet
pressure is < 0.2 mbar (20 Pa).
Is the backing pressure < 12 mbar
(1200 Pa)?
Check for backing line leaks. If the
backing pressure is too high, a larger
backing pump may be required.
Is the high-vacuum area of the
system contaminated?
If so, clean the high-vacuum system.
Check the rest of the system for
leaks and contamination.
If found, clean the contaminated
areas and repair the leaks.
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 the 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 the supplier.
Is the EXT pump making a constant
high-pitched noise?
If so, the rotor is out of balance.
Consult Edwards or the supplier.
None of the above.
Consult Edwards or the supplier.
