Agilent Technologies G4782A, User Manual

Page: 60 / 202

60 1260 SFC Binary Pump
4
Optimizing Performance
How to Optimize the Compressibility Compensation Setting
How to Optimize the Compressibility Compensation Setting
When a solvent is metered at ambient pressure and compressed to a higher
pressure, the volume decreases depending on its compressibility. Solvent
compressibility is a non-linear function of pressure and temperature. It is
specific for each solvent.
In order to deliver the desired flow accurately at all pressures, Agilent pumps
use a compressibility compensation. For standard LC applications, e.g. using a
400 bar binary pump, an average compressibility value for the solvent is
sufficient.
For the 600 bar 1260 Infinity II Binary Pump , the pressure-dependency of a
solvent compressibility needs to be considered. It is determined at different
pressures between 0 – 600 bar. The pump uses the obtained non-linear
function to select the correct compressibility value for the actual pump
pressure. Compressibility data for the most common solvents is readily
available in the pump firmware.
The compensation algorithm is so powerful that the damper and mixer can be
removed from the pump flow path at low flow rate while the pressure ripple
and composition ripple remain at low levels.
For method compatibility reasons, the legacy compressibility compensation is
still available.
Optimization of Legacy Compressibility Settings
The compressibility compensation default settings are 50 × 10
-6
/bar (best for
most aqueous solutions) for pump head A and 115 × 10
-6
/bar (to suit organic
solvents) for pump head B. The settings represent average values for aqueous
solvents (A side) and organic solvents (B side). Therefore it is always
recommended to use the aqueous solvent on the A side of the pump and the
organic solvent on the B side. Under normal conditions, the default settings
reduce the pressure pulsation to below 2 % of system pressure, which is
sufficient for most applications. If the compressibility values for the solvents
used differ from the default settings, it is recommended to change the