Metrohm 807 Dosing Unit - Manual (Page 28)

3.6 Avoiding air bubbles
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807 Dosing Unit
CAUTION
A small air bubble will also always be present on the piston after a
PREP-Preparing step. It will however not be expelled during the dosing.
An air bubble of that small size will not have any effect on the precision
of a dosing! (see Figure 14, page 20)
A
B
Figure 14 Air bubbles in the cylinder
The end position A (end volume) will never be exceeded by the piston dur-
ing dosing procedures. It is only with the PREP function that the piston
will be moved all the way to the stop (PREP Position B).
A dead volume will always remain after dosing which is greater in size
than any air bubble which might remain following the execution of the
PREP/Preparing function (see arrow). This means that the latter cannot
exit into the tubing system and impair the precision of the dosing. The air
bubble remains in the dosing cylinder.
Conclusion
The design and mode of operation of the dosing unit is constructed in
such a way that air bubbles which could possibly arise in the system will
not be able to escape unchecked. They can be expelled efficiently prior to
the dosing with the PREP function. Any small air bubbles which might
form will be held back in a bubble trap. They exercise no influence over
the dosing.