How Does Compressibility Compensation Work; How Does Variable Stroke Volume Work - Agilent Technologies 1200 Series Reference Manual

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 plunger. The pressure in the plunger 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 is depending on the backpressure in the system and the selected
compressibility. This compensation volume will be added to the normal stroke
volume and compensates the previous described loss of volume during the
delivery stroke of the first plunger.

How Does Variable Stroke Volume Work?

Due to the compression of the pump-chamber volume each plunger stroke of
the pump will generate a small pressure pulsation, influencing the flow ripple
of the pump. The amplitude of the pressure pulsation is mainly dependent on
the stroke volume and the compressibility compensation for the solvent in use.
Small stroke volumes will generate pressure pulsations of smaller amplitude
than higher stroke volumes at same flow rates. In addition the frequency of the
pressure pulsations will be higher. This will decrease the influence of flow
pulsations on quantitative results.
In gradient mode smaller stroke volumes resulting in less flow ripple will
improve composition ripple.
The quaternary pump uses a processor-controlled spindle system to drive its
plungers. 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.
1200 Series QP Reference Manual
Introduction to the Quaternary Pump 7
207