Watson-Marlow PD22I - Manual (Page 12)

OPERATORS MANUAL Machine Type: PD22I / PD22P
PD22 I P OM 1.01 EN Ver 1.01 Date 24-08-2006 Page 12 of 21
Filling with large volume and high surface tension might have tendency to suck air back in the
filling line.
6.4 Priming tubes
In order to evacuate air from the tubes and prepare the tubes for filling, it is necessary to prime
the tubes. Priming must be done adequately and continued until the tube material hysteresis
disappears as well as any air bubbles.
6.5 Drip
When dispensing very small volumes, the last drop of the filling constitutes a big part of the
total filling. Therefor it is necessary to take necessary measures for avoiding the last drop. For
small volumes a dumping nozzle system can be applied to eliminate the last drop of filling.
When dispensing with very large volumes, the shape of nozzle and the filling speed required
may not always be compatible. For this reason consideration should be done if using non-return
valve or forced back-suction is necessary.
Flexicon dispensers offer back-suction (reversing) after every individual dispensing.
6.6 Hard Feed
When dispensing with small tubes, counter pressure on the pressure side of pump head might
constitute inaccuracy and instability in filling (hard feed). In some cases the problem can be
resolved by using a larger tube on the pressure side (after Y-connector).