Metrohm 792 Basic IC - Manual (Page 157)

5 Notes – Maintenance – Faults
792 Basic IC
148
x To install a new piston seal 89
89 89 89 the special tool 94 94 94 94 is used.
x First the new seal is inserted firmly in the recess of tool 94
94 94 94 by
hand (see Fig. 17B). The seal spring must be located on the
outside.
x The tool 94 94 94 94 together with the seal is then inserted in the pump
head 34 34 34 34 and the seal pressed into the pump head recess
with the aid of tool 93 93 93 93 (see Fig. 17C).
The seal surface in the pump head 34 34 34 34 must not be damaged (avoid
contact with tool)!
5 Cleaning/replacement of inlet valve 90 90 90 90 and outlet
valve 91 91 91 91
x 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).
x If this does not have the desired effect, the valves can be
disassembled as shown in Fig. 18. The valve components are
pushed out with the aid of a syringe needle inserted through
the upper opening in the valve housing 95 95 95 95. 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. 18. The compo-
nents of the inlet and outlet valves are identical, they are dis-
tinguished only by the positioning of the sapphire sleeve 98 98 98 98
and the ceramic holder 100 100 100 100 (see Fig. 18).
x Valves that fail to function faultlessly after such cleaning must
be replaced.
x In the reinstallation of the inlet valve 90
90 90 90 or the outlet valve 91 91 91 91
on no account must the two outwardly identical valves be in-
terchanged. 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. 18).
If by mistake an inlet valve 90 90 90 90 is installed instead of the outlet valve 91 91 91 91,
an extreme pressure buildup occurs within the working cylinder, which
is not detected by the pressure transducer and will destroy the piston
seal 89 89 89 89!