Thermo Scientific Dionex UltiMate 3000 Series, Operating Instructions Manual

Page: 121 / 270

UltiMate 3000 Series:
NCS-3500RS and NCP-3200RS
Operating Instructions Page 113
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
max
and the viscosity of the higher-viscosity solvent:
MPa
P MPa
ity cos Vis
%
Flow al min No Flow max
max
20
100
100
−
⋅ ⋅ =
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:
min / nL
MPa
MPa MPa
%
%
min / nL Flow
max
875
20
65 100
100
100
500 =
−
⋅ ⋅ =
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.