Metrohm 700 Dosino - Manual (Page 32)

3. The Dosino in practice
700 Dosino, Instructions for Use
26
3.1 Air bubbles are (almost) inevitable
As a result of leaky tubing connections or the release of dissolved
air from the liquid to be dosed it is possible that air bubbles could
collect in the dosing cylinder.
Always check the tubing ends for damage before you attach the
tubings. Please ensure that tubing connections are always tight.
Always tighten up the screw nipples firmly by hand and take care
that you do not damage the tubing ends when doing this.
All Metrohm instruments which support Dosinos as dosing drives
possess a
'PREP' function. This function is a preparation step in
which the cylinder and tubing are automatically filled with liquid.
In order for the control instrument to be able to calculate the cor-
rect amount of rinsing solution required it is necessary to enter the
lengths and diameters of all the connected filling and dosing tub-
ing. This is carried out in the dosing unit configuration of the par-
ticular instrument.
Always use the 'PREP' function before you use a dosing unit
for the first time, i.e. before you start a sample series carry
out the 'PREP' function first (at least once per day).
Further details are given in the ‘Instructions for Use’ of your
Metrohm instrument.
Please note:
With the
'PREP' function the existing cylinder contents are com-
pletely ejected. The piston moves beyond the normal maximum
position (10'000 impulses) and presses against the cylinder base.
The piston can never completely fill the whole of the cylinder base
so that a small air bubble may remain in position.
Even after a 'PREP' preparation step there will
always be a small air bubble at the piston. It
will not escape the cylinder.
However, such a small air bubble
does not af-
fect the precision of a dosing process!
For details please refer to the drawing on the following page.