Agilent Technologies 1260 Infinity VL User Manual page 15

How Does Compressibility Compensation Work?
The compressibility of the solvents in use will affect retention-time stability
when the back pressure in the system changes (for example, ageing of
column). In order to minimize this effect, the pump provides a compressibility
compensation feature which optimizes the flow stability according to the
solvent type. The compressibility compensation is set to a default value and
can be changed through the user interface.
Without a compressibility compensation the following will happen during a
stroke of the first piston. The pressure in the piston chamber increases and
the volume in the chamber will be compressed depending on back pressure
and solvent type. The volume displaced into the system will be reduced by the
compressed volume.
With a compressibility value set the processor calculates a compensation
volume, that depends on the back pressure of the system and the selected
compressibility. This compensation volume will be added to the normal stroke
volume and compensates the previously described loss of volume during the
delivery stroke of the first piston.
How Does Variable Stroke Volume Work?
Due to the compression of the pump-chamber volume each piston stroke of the
pump will generate a small pressure pulsation, influencing the flow stability of
the pump. The amplitude of the pressure pulsation depends mainly on the
stroke volume and the compressibility compensation for the solvent in use.
Small stroke volumes generate pressure pulsations of smaller amplitude than
higher stroke volumes at the same flow rate. In addition, the frequency of the
pressure pulsations is higher. This decreases the influence of flow pulsations
on quantitative results.
In gradient mode smaller stroke volumes result in a lower flow ripple improve
composition ripple.
The module uses a processor-controlled spindle system for driving its pistons.
The normal stroke volume is optimized for the selected flow rate. Small flow
rates use a small stroke volume while higher flow rates use a higher stroke
volume.
By default, the stroke volume for the pump is set to AUTO mode. This means
that the stroke is optimized for the flow rate in use. A change to larger stroke
volumes is possible but not recommended.
1260 Infinity QuatPump VL User Manual
Introduction
Overview of the Hydraulic Path
1
15