How Does Compressibility Compensation Work; How Does Variable Stroke Volume Work - Agilent Technologies InfinityLab LC Series User Manual

1 Introduction
Overview of the Hydraulic Path

How Does Compressibility Compensation Work?

The compressibility of the solvents in use will affect retention-time stability when
the backpressure in the system changes (for example, aging of column). 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 backpressure 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 backpressure 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 and will
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.
Agilent InfinityLab LC Series 1260 Infinity II Isocratic and Quaternary Pumps User Manual 25