1
Introduction
Functional Description
Thermo Scientific
Accela Pump Hardware Manual
3
The following topics describe the main features of the Accela Pump:
•
Vacuum Degasser Assembly
•
Liquid Displacement Assembly (LDA)
•
Purge Valve
•
Pulse Dampening Assembly
•
Dynamic Mixer
•
Status LEDs
Vacuum Degasser Assembly
The Accela Pump contains a built-in vacuum membrane degasser that removes dissolved
gasses from the mobile phase. Dissolved gasses can cause many problems in HPLC and must
be kept to an absolute minimum for best performance. The solvent degassing system consists
of four independent channels that are maintained at a constant vacuum of approximately
50 mm Hg absolute. Each channel has a volume of less than 500
μ
L, which provides superior
degassing efficiency capable of limiting dissolved oxygen to a level of only 0.8 ppm. By
varying its speed, the vacuum pump maintains a constant vacuum level. This eliminates the
excess baseline noise and drift caused by vacuum pump cycling.
Liquid Displacement Assembly (LDA)
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
sapphire pistons and their seals, upper and lower piston chambers, and various PEEK seal
rings. The inlet module 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 gradient delay volume to only 65
μ
L.
As the lower piston withdraws, mobile phase from the proportioning valve assembly passes
through the inlet check valve and fills the lower piston chamber. As 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 out the front of the outlet module.
The proportioning valves of the Accela Pump 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
Note
The dynamic mixer adds an additional 35
μ
L of gradient delay volume.
