Unstable Column Flow And/Or System Pressure - Agilent Technologies 1100 Series Service Manual

2 Troubleshooting and Test Functions

Unstable column flow and/or system pressure

In the micro mode, the pump flow control system is active. The flow control
system continuously measures the actual value of column flow, and maintains
the requested column flow despite changes in system restriction. If the flow
control becomes defective, actual column flow, hence system pressure, will
fluctuate. If the system offers a changing restriction to the pump, actual
column flow will fluctuate as the pump tries to maintain flow against the
changing restriction. Therefore, in the micro mode, unstable column flow and
unstable system pressure usually appear together.
Table 9 Unstable column flow and/or system pressure: Possible Causes and Suggested Actions
Possible Causes
The flow setpoint is below the
recommended minimum
value.
The system pressure is
insufficient for reliable flow
control (micro mode).
Leaks somewhere in the
system.
One or more solvent channels
are not correctly purged.
%Ripple might also be too
high.
Dirty solvent inlet filters.
Solvent intake is being
restricted. %Ripple might
also be too high.
96
Suggested Actions
• Make sure that the column flow setpoint is
above the recommended minimum setpoint:
• Make sure that there is at least 20 bar pressure
being developed after the pump.
• Add an additional capillary after the pump if
required.
• Use a flashlight and absorbent tissue to search
for leaks throughout the system. Check for leaks
after the pump, and inside the pump (valves,
fittings, etc.)
• If operating in the micro mode, perform the
micro mode pressure test. If operating in the
normal mode, perform the normal mode
pressure test.
• Perform a 2-minute purge at 2500 µl/min for
each solvent channel.
• Temporarily remove solvent inlet filters to see if
they are the cause of the problem. If so, clean or
replace the solvent inlet filters.
Notes
Normal mode 100 µl/min
Micro mode, 20 µl flow sensor
1 µl/min
Micro mode, 100 µl flow sensor
10 µl/min
At very low flow rates, a leak may
never accumulate enough liquid to
trigger the module leak sensors. Low
flow rate leaks are also very hard to
see.
Refer to the Nano Pump Service
Manual "Testing your Nano Pump"
on page 65, "Normal Mode Pressure
Test" on page 68.
This is especially likely if the system
has been unused for more than one
day.
To minimize this problem, prefilter
the mobile phase, and take
precautions against algae formation
in the water.
1100 Series Nano Pump Service Manual