Dionex UltiMate 3000 Series, Operating Instructions Manual

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UltiMate 3000 Series:
SD, RS, and BM Pumps
Operating Instructions Page 15
2.3 Operating Principle
The pump is a zero-pulsation, serial dual-piston pump with electronic compressibility
compensation. The pump head includes two cylinders—working cylinder and equilibration
cylinder—that are connected in series. The solvent passes both cylinders successively.
Continuous delivery is achieved as follows: The working cylinder delivers at the
appropriate flow rate while simultaneously filling the serially connected equilibration
cylinder. The latter serves as a reservoir and delivers while the working cylinder carries
out the suction stroke.
The characteristic feature of the patented isokinetic pre-compression is the overlapping phase
of the delivery strokes of the working and equilibration cylinders. When delivering
compressible liquids without controlled pre-compression, the pulsation increases as the
working pressure increases, since part of the delivery stroke is required for compressing the
solvent in the working cylinder. Pulsation during the pre-compression phase is reduced to a
minimum by velocity modulation of the drive. The highly constant delivery is ensured by a
patented secondary control system (automatic compressibility compensation). The flow rate is
always kept constant in relation to the atmospheric pressure.
The schematics in section 8 illustrate how the pumps operate (

page 161).