Watson-Marlow PF22 - Manual (Page 19)

Operators Manual
PF22
PF22 OM EN 74-132-005 v1.02.doc Version: 1.02 Page 19 of 34
Nature of fill media
The peristaltic dispensers are not suitable for viscous products. For viscous products another
type of dispenser from Flexicon can be used. In the case that the PF22 should be used and the
product is of viscous nature, then heating the product before dispensing with PF22 is
recommended.
Another consideration is the surface tension of the liquid. Products with high surface tension tend
to produce dripping. Due to this fact it is difficult to have sufficient cut off after every individual
dispensing. When filling with small volumes and high surface tension present drips are often
produced and constitute inaccuracy.
Filling with large volume and high surface tension might have tendency to suck air back in the
filling line.
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 controlling the last drop. For small
volumes reverse suction or a dumping nozzle system can be applied to control the last drop of
filling.
When dispensing very large volumes, the shape of the 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.
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). For example if using 3.0
in the pump head, then Ø5.0 might be used as connection to filling point (feed side). Keep the
feed line as short as possible.