PuK - Process Technology & Components 2024

Pumps and Systems
Diaphragm metering pumps
motor or permanent magnet synchronous
motor (PMSM) is variable
and operating points can be approached
precisely and reproducibly
without manual stroke adjustment
– thus making them compliant with
GMP. At ±1 percent, metering accuracy
is extremely accurate. To prepare
the mixtures in the chromatographic
environment, the flow rates
of the individual pump lines must be
precisely maintained. For this purpose,
they are determined by Coriolis
flow meters and precisely controlled
at the specified target values using
the speed control of the pumps. Additional
online monitoring of the pH
value and electrical conductivity ensures
continuous control of the process
conditions.
To ensure that the specified accuracies
are maintained over wide adjustment
ranges, correct suction-side
pressures (NPIPA) must be ensured
at the pumps. The abbreviation NPIP
stands for “Net Positive Inlet Pressure”
and NPIPA for “Net Positive Inlet
Pressure Available”. The NPIP is similar
to the well-known NPSH, although
the latter is only defined by the
height. In contrast, the NPIPA is the
measure of the pump inlet pressure
present at the inlet valves through
the system. The NPIP is determined
Fig. 6: Pressure control unit for adjusting constant damped fluid flows upstream of chromatography
columns. (Source: EQUILIBAR)
by the static pressure upstream of
the pump, for example by a vessel
with or without pressure superposition
or by the pressure in closed circular
piping. If the NPIP is too low, cavitation
may occur in the pump heads
if the steam pressure falls below the
value specified. If, on the other hand,
a diaphragm metering pump has a
net suction pressure that is too high,
there is a risk of excessive and uncontrolled
flow, particularly with low
metering quantities in pumps that do
not have built-in valve springs due
to hygiene requirements, which can
impair metering accuracy and dilution
rate. To control the pump-specific
hydraulic conditions, pressure
(retaining) control valves are therefore
used on the discharge side of
the pumps after all installations with
pressure losses to ensure a constant
max. 4.000 bar
max. 10.000 l/min
max. 600 m 3 /h
max. 3000 kW