1260 Infinity Binary Pump User Manual 15
Introduction to the Binary Pump
1
Overview of the Hydraulic Path
What is Pump Elasticity Compensation?
The flow path of the pump consists of pump chambers, sapphire pistons,
polymer seals, stainless steel tubing of different dimension, pressure
sensor, and so forth. All of these parts deform when pressurized. The sum
of this deformation is called pump elasticity.
Let us look at a practical example: Piston 1 draws solvent at ambient
pressure. The movement direction is reversed and the piston 1 now
compresses the solvent until the operating pressure of the HPLC system is
reached. The outlet valve opens, and solvent is pumped by piston 1 into
pump chamber 2. Due to two factors, the solvent volume that is delivered
into the system at high pressure is smaller than it is supposed to be:
1 The solvent is compressible
2 The pump has a certain elasticity which causes its internal volume to
increase with pressure.
In order to compensate for these two influences, their contributions must
be known. An elasticity calibration allows separating pump properties
from solvent properties and therefore allows transferring solvent
properties, which have been obtained from one pump to another pump
with different elasticity.
Elasticity calibration is done with a solvent, which properties
(compressibility, thermal expansion) are well- known and documented:
pure water. When pumping water and using its property data for
controlling the pump, any deviations from the theoretical pressure profile
during solvent recompression are caused by the elasticity of the pump.
The Pump Elasticity Calibration calculates correction factors to
compensate for the individual elasticity of the pump that is being
calibrated. The elasticity is different for every pump and may change with
the replacement of parts in the flow path, e.g. pump seals.
All binary pumps are elasticity calibrated at the factory and require
recalibration only after preventive maintenance or major repairs to the
flow path. Replacement of capillaries or PTFE frits are not considered as
a major repair.
Incorrect pump elasticity calibration.
Solvent compressibility calibrations acquired with a miscalibrated pump will work, but
they are not transferable to other pumps. A correct pump elasticity calibration is an
essential prerequisite for successful solvent compressibility calibrations.
➔ Calibrate the pump elasticity correctly.
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