User manual

12 1260 Nanoflow Pump User Manual
1 Introduction to the 1260 Infinity Nanoflow Pump
Introduction to the Pump
How Does the Pumping Unit Work?
Both pumping units (channel A and channel B) are identical with respect to
parts and function. Each pumping unit consists of a pump head which is
directly attached to a metering drive assembly.
In each metering drive assembly, a servo-controlled variable reluctance motor
and gear train assembly are used to move two ball-screw drives. The gear train
moves the two ball-screw drives in opposite directions (180 degree out of
phase). The gear ratios are designed such that the first ball-screw drive
constantly moves at twice the speed of the second ball-screw drive.
The servo motor includes a high resolution shaft-position encoder, which
continuously reports the speed and direction of the motor in real time. This
speed and direction information is used by the pump control electronics to
ensure precise control of the servo motor movement.
Each pump head consists of two identical chambers, pistons and seals, plus an
active inlet valve and an outlet valve. The solvent volume in each chamber is
displaced by its piston. The pistons are directly moved by the reciprocating
ball-screw drives of the metering drive assembly. Due to the gear design of the
metering drive assembly, the pistons move in opposite directions, with piston
1 constantly moving at twice the speed of piston 2. The outer diameter of the
piston is smaller than the inner diameter of the chamber, allowing solvent to
flow in the gap between the piston and the chamber wall. The two chambers
are connected by the pressure dependent outlet valve.
The position of the solvent selection valve determines which of two solvents
will be sucked (low pressure) through the active inlet valve into chamber 1
during the intake stroke of piston 1. The active inlet valve is electrically
opened and closed, making its operation more precise at low pressures. The
stroke volume of piston 1 is between 2µL and 100µL, depending on flow rate.
When the pump is first turned on, the user is prompted to initialize the pump.
The initialization routine (occurring for both pump heads) first determines the
precise movement limits for both pistons.These limits are then stored in the
pump controller memory. Then, both pistons are set to their default initial
positions.
When pumping begins, the active inlet valve is opened and piston 1 begins its
intake stroke, sucking solvent into chamber 1. At the same time, piston 2
begins its delivery stroke, pumping (high pressure) the existing solvent in
chamber 2 out of the pump head. The pressure produced by piston 2 also