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Vacuum Degasser Assembly
Liquid Displacement Assembly
Thermo Scientific
The Surveyor MS Pump Plus contains a built-in vacuum membrane degasser for the purpose
of removing dissolved gases from the mobile phase. Dissolved gases can cause many problems
in HPLC and must be kept to an absolute minimum for best performance. The MS pump
solvent degassing system consists of four independent channels that are maintained at a
constant vacuum of approximately 686 mm (27 in.) Hg. Each channel has a volume of less
than 500 μL, which provides superior degassing efficiency capable of limiting dissolved
oxygen to a level of only 0.8 ppm. The system's vacuum pump operates continuously, which
eliminates the excess baseline noise and drift caused by vacuum pump cycling.
The frame of the liquid displacement assembly (LDA) consists of two components: the LDA
body and the inlet module. The LDA body contains the inlet and outlet check valves, two
TZP-ceramic pistons and their seals, an upper and lower piston chamber, a pressure
transducer, and various PTFE seal rings (see
contains a built-in low volume mixer. Four high-precision proportioning valves are connected
to the inlet module. And four actuating coils are connected to the ends of the proportioning
valves. All of these components are integrated into a single mechanical-hydraulic assembly,
which minimizes the pump's gradient delay volume to only 80 μL.
As the lower piston withdraws, mobile phase from the proportioning valve assembly passes
through the inlet check valve and fills the lower piston chamber (see
the lower piston returns, the inlet check valve closes and the mobile phase is pushed through
the outlet check valve and into the upper piston chamber. Both check valves are low volume
and incorporate a dual ball and seat design, which ensures a positive seal with minimal delay
volume.
Next, the upper piston moves into the upper piston chamber, closing the outlet check valve
and forcing the mobile phase into the pressure transducer housing. On the next piston stroke
the mobile phase is pushed out of the LDA and into the crossover tube that is attached to the
pulse dampening assembly.
The proportioning valves of the Surveyor MS Pump Plus incorporate a finely machined ball
and seat design similar to a check valve. This ball and seat design controls the flow of solvents
to a higher degree of precision and accuracy than the diaphragm design used by most gradient
pumps. In addition, the ruby ball and sapphire seat are virtually wear free as opposed to the
polymeric membrane of a diaphragm valve, which becomes more brittle and less responsive as
it ages.
There is a venting valve on the left side of the LDA. When the venting valve is open, the
mobile phase exits out the left end of the pressure sensor assembly. When the venting valve is
closed, the mobile phase is directed out of the front of the pressure sensor assembly and into
the crossover tube.
Figure 3
purging.
Figure 75
shows a pump with the venting valve in the open position for
Surveyor MS Pump and Surveyor MS Pump Plus Hardware Manual
Functional Description
on
page
77). The inlet module
Figure 75
on
1
Introduction
page
77). As
3
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