Metrohm 761 Compact IC - Manual (Page 188)

5 Notes – Maintenance – Faults
761 Compact IC
178
• To install a new piston seal 112 the special tool 117 is used.
• First the new seal is inserted firmly in the recess of tool 117
by hand (see Fig. 20B). The seal spring must be located on
the outside.
• The tool 117 together with the seal is then inserted in the
pump head 42 and the seal pressed into the pump head re-
cess with the aid of tool 116 (see Fig. 20C).
The seal surface in the pump head 42 must not be damaged (avoid
contact with tool)!
5 Cleaning/replacement of inlet valve 113 and outlet
valve 114
• Contaminated or blocked valves are cleaned by rinsing with
dist. water, RBS solution or acetone. The rinsing effect can be
reinforced by brief treatment in an ultrasonic bath (max. 20 s;
if longer the sapphire sphere of the valve can be damaged).
• If this does not have the desired effect, the valves can be
disassembled as shown in Fig. 21. The valve components are
pushed out with the aid of a syringe needle inserted through
the upper opening in the valve housing 118. The individual
components are rinsed with dist. water and/or acetone, and
the sapphire sphere cleaned with a paper towel. The valve is
then reassembled in accordance with Fig. 21. The compo-
nents of the inlet and outlet valves are identical, they are dis-
tinguished only by the positioning of the sapphire sleeve 121
and the ceramic holder 123 (see Fig. 21).
• Valves that fail to function faultlessly after such cleaning must
be replaced.
• In the reinstallation of the inlet valve 113 or the outlet valve
114 on no account must the two outwardly identical valves be
interchanged. To determine which valve is which, note that
the liquid flows through the pump head from the bottom up.
The flow direction of the valves can be checked simply by
blowing through the clean valve. Both valves are installed with
the black face in the direction of the pump head (see Fig. 19).
If by mistake an inlet valve 113 is installed instead of the outlet valve
114 , an extreme pressure buildup occurs within the working cylinder,
which is not detected by the pressure transducer and will destroy the
piston seal 112 !