Thermo Scientific Dionex UltiMate 3000 Series Operating Instructions Manual page 121

Classic flow meter: Interdependency of column pressure and the maximum flow rate
The pump has been designed for column pressures of up to 80 MPa. This value refers to
the nominal flow and solvents with a maximum viscosity of 100 % (equivalent to water).
The primary pressures can be up to 100 MPa, but the flow restrictors cause a pressure drop
that depends on the selected flow rate, the viscosity of the solvents, and the solvent
composition.
Thus, the column pressure that is actually available depends also on these parameters.
The maximum allowed flow rate can be calculated from the expected column pressure P
and the viscosity of the higher-viscosity solvent:
Flow
Example:
Nominal flow: 500 nL/min
Solvent A = water (viscosity: 100%)
Solvent B = 80% ACN with 20% water (viscosity: 65%)
Maximum expected column pressure: 65 MPa
Solvent B is the lower-viscosity solvent and thus can be ignored. This means:
Flow
max
The Ready Check checks whether the selected flow rate can be reliably delivered with the
selected maximum column pressure (→ page 120). A message appears if this is not
possible. If the upper limit for the column pressure is set to a value that is considerably
higher than the actually expected column pressure, the message may appear although the
problem does not yet exist. In this case, reduce the upper limit as required.
If you are really working at very high column pressures and the selected flow cannot be
delivered, reducing the flow rate and pressure limit slightly will usually be sufficient to
remedy the situation, as the maximum expected column pressure decreases with the flow rate.
During operation, the pump continuously monitors whether the selected flow rate is actually
delivered. If it is not, a message appears ('Cannot deliver desired flow at this pressure') and the
batch will be aborted. A number of factors, for example, the selected gradient, determine
whether this situation will actually occur.
Operating Instructions
No min al Flow
=
max
100 %
nL / min
= 500 ⋅
%
100
NCS-3500RS and NCP-3200RS
100 MPa
100 %
⋅ ⋅
Vis cos ity 20 MPa
100 MPa − 65 MPa
⋅ =
MPa
20
UltiMate 3000 Series:
max
− P
max
nL / min
875
Page 113