ICS-3000 Ion Chromatography System
20 Doc. 065031-04 1/08
2.2.1 Pump Heads
The DP/SP is a zero-pulsation, serial dual-piston pump with electronic
compressibility compensation. Two pump heads—a primary head and a
secondary head—are connected in series. Eluent passes through both
pump heads in succession.
The primary pump head delivers eluent at the selected flow rate, while
simultaneously filling the secondary pump head. The latter serves as a
reservoir and delivers eluent while the primary head carries out the refill
stroke.
The characteristic feature of the patented isokinetic pre-compression
phase is the programmed overlapping of the delivery strokes of the two
pump heads. When delivering compressible liquids without controlled
pre-compression, the pulsation increases as the operating pressure
increases, since part of the delivery stroke is required to compress eluent
in the pump head.
During the pre-compression phase, pulsation is minimized by velocity
modulation of the drive. A patented secondary control system (automatic
compressibility compensation) ensures highly constant eluent delivery.
The flow rate remains constant in relation to the pressure.
2.2.2 Pressure Transducer
The secondary pump head contains a built-in pressure transducer to
measure the system pressure. The DP/SP Moduleware (the instrument
control firmware installed in the pump) precisely controls the pump motor
speed to ensure flow rate accuracy and to maintain constant flow and
constant pressure.
Flow output from the secondary pump head passes through a static mixer
(described in Section 2.2.6
) before being directed to the remainder of the
chromatography system (the injection valve, columns, and detector).
2.2.3 Proportioning Valves (Gradient pump only)
In the gradient pump, eluent flows from the eluent reservoirs, through the
vacuum degas chambers, and into a four-way proportioning valve
assembly (see Figure 2-3
). Programmed percentages of each eluent are
proportioned by the four valves.
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