Metrohm 792 Basic IC - Manual (Page 155)

5 Notes – Maintenance – Faults
792 Basic IC
146
5.2.6 Maintenance work at the pump head
In many cases, an unstable baseline (pulsation, flow fluctuations) can
be traced to contaminated valves or faulty, leaky piston seals at the
high-pressure pump. For cleaning contaminated valves and/or re-
placement of wear parts such as pistons, piston seals and valves, pro-
ceed as follows:
1 Detach pump head
x Disconnect aspirating tubing from aspirating capillary 32
32 32 32 at
the pump head 34 34 34 34 (see Fig. 3).
x Unscrew connection capillary 35
35 35 35 from the pump head 34 34 34 34.
x Remove pump head 34 34 34 34 by loosening the 4 hexagon screws
33 33 33 33 using the 6.2621.030 Hexagon key. The main piston is on
the left (when viewed from front), the auxiliary piston on the
right.
2 Disassemble pump head
x Strip down pump head 34 34 34 34 in accordance with Fig. 16. Main
and auxiliary pistons are identical with the following excep-
tions:
The spring 84
84 84 84 of the auxiliary piston (right piston) is more
powerful (longer) than that of the main piston (left piston).
Inlet and outlet valve are not present in the secondary cylin-
der.
To prevent the piston 82 82 82 82 suddenly jumping out of the piston cartridge
85 85 85 85, the screw 81 81 81 81 must be undone very carefully by hand.
3 Cleaning/replacement of piston 82 82 82 82
x Pistons contaminated by abrasive particles or deposits are
cleaned with scouring powder and rinsed free of any particles
with dist. water.
x Relatively badly contaminated or scratched pistons must be
replaced (spare part: 6.2824.070 Zircon piston).
4 Replacement of piston seal 89 89 89 89
x To remove damaged piston seals 89
89 89 89 the special tool 93 93 93 93 is
used. This is screwed into the seal 89 89 89 89, which can then be
pulled out (see Fig. 17A).
When the special tool 93 93 93 93 is screwed into the piston seal 89 89 89 89 the latter is
completely destroyed!