Metrohm 752 Pump Unit - Manual (Page 21)

4 Troubleshooting
752 Pump Unit
18
4.3 Air bubbles in pump circuit
If air bubbles can be seen in the pump circuit then the aspirating tubing
must be immersed completely in the liquid. If this has no effect then the
connections must be checked (see section 4.2).
4.4 Exchanging the pump tubing
Pump tubings are consumable material with a limited lifetime and
should be exchanged at regular intervals (approx. every 2 weeks under
continuous use).
The working life of pump tubing depends to a considerable extent on
the contact pressure. This is why the contact pressure must be cor-
rectly set as described in section 2.3.2. If the pump is to remain
switched off for a lengthy period of time the tubing cartridges should be
raised completely by loosening snap-action lever 77 on the right-hand
side (the set contact pressure remains unchanged).
As the pump is always operated on the same side the pump tubings
6.1826.050 supplied can be used on both sides. To exchange a pump
tubing proceed as follows:
1 Remove old pump tubing
• Press contact pressure lever 55 on the tubing cartridge down
as far as it will go.
• Release tubing cartridge 44 from holding clamp 66 by pressing
down snap-action lever 77 and remove from mounting pin 99
on the 752 Pump Unit (see Fig. 1).
• Remove old pump tubing.
2 Insert new pump tubing
• Insert the new pump tubing 18 18 (6.1826.050) in the tubing
cartridge as shown in Fig. 6. The white-yellow stopper 19 19
must click into the corresponding holder on the left-hand side
of the tubing cartridge.
• Place the tubing cartridge on mounting pin 99 and press down
on the right-hand side until snap-action lever 77 clicks into po-
sition on holding clamp 66. Take care that no kinks are formed
in the pump tubing.
3 Set contact pressure
• Press contact pressure lever 55 upwards until the solution just
starts to be drawn in. Then press contact pressure lever up-
wards until it clicks once more to obtain optimal contact pres-
sure.