Metrohm 940 Professional IC Vario ONE/SeS/PP/Prep 3 - Manual (Page 92)

5.8 Servicing the high-pressure pump
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940 Professional IC Vario ONE/SeS/PP/Prep 3 (2.940.1530)
Optional: Cleaning/replacing the zirconium oxide piston
If the baseline still remains unstable after replacing the valves and piston
seal, the zirconium oxide piston in the high-pressure pump may be dirty or
scratched. In that case, the zirconium oxide piston must have to be
cleaned or replaced.
Clean one piston cartridge after the other as follows:
Accessories For this task you need the following accessories:
You can find these parts in the accessory kit: Vario/Flex Basic
(6.5000.000).
￭ Adjustable wrench (6.2621.000)
Spare parts For this first step you need a new zirconium oxide piston (6.2824.070).
Optional: Cleaning/replacing the zirconium oxide piston
Prerequisites:
￭ The pump head has been removed (see "Removing the pump head",
page 77).
￭ The piston cartridge is removed (see "Replacing the piston seal", page
78).
1 Breaking down the piston cartridge
CAUTION
Inside the piston cartridge there is a taut spring that can launch
out of the piston cartridge if the tension is released suddenly.
When opening the piston cartridge, counteract the pressure from
the spring and carefully unscrew the cartridge.
￭ Loosen the piston cartridge's screw with an adjustable wrench
and carefully unscrew the screw by hand while counteracting the
pressure from the taut spring.
￭ Remove the zirconium oxide piston and place it on a paper towel.
￭ Remove the spring retainer, spring and the inner plastic sleeve
from the piston cartridge and lay them next to the piston.
￭ Place the backup ring you put aside with the remaining parts.