Watson-Marlow PD12I - Manual (Page 12)

INSTRUCTION HANDBOOK
PD12I / PD12P
PD12IP IH 1.03 EN Version: 1.03 Page 12 of 20
5.3 Nature of fill media
The peristaltic dispensers are not suitable for viscous products. For viscous product another
type of dispenser from WM Flexicon can be used. In the case that the PD12 should be used
and the product is of viscous nature, then heating the product before dispensing with PD12 is
recommended.
Another consideration is the surface tension of liquid. Product with high surface tension tends
to produce drip. Due to this fact it is difficult to have sufficient cut off after every individual
dispense. When filling with small volumes and high surface tension present drips are often
produced and constitute inaccuracy.
5.4 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.
5.5 Drip
When dispensing very small volumes, the last drop of the filling constitutes a big part of the
total filling. Therefore it is necessary to take measures for avoiding the last drop.
WM Flexicon dispensers offer back-suction (reversing) after every individual dispensing.
5.6 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).