Metrohm 761 Compact IC - Manual (Page 186)

5 Notes – Maintenance – Faults
761 Compact IC
176
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
• Disconnect aspirating tubing 63 from aspirating capillary 40
at the pump head 42 (see Fig. 3 and Fig. 4).
• Unscrew connection capillary 43 from the pump head 42.
• Remove pump head 42 by loosening the 4 hexagon screws
41 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
• Strip down pump head 42 in accordance with Fig. 19. Main
and auxiliary pistons are identical with the following excep-
tions:
− The spring 107 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 105 suddenly jumping out of the piston cartridge
107 , the screw 104 must be undone very carefully by hand.
3 Cleaning/replacement of piston 105
• Pistons contaminated by abrasive particles or deposits are
cleaned with scouring powder and rinsed free of any particles
with dist. water.
• Relatively badly contaminated or scratched pistons must be
replaced (spare part: 6.2824.070 Zircon piston).
4 Replacement of piston seal 112
• To remove damaged piston seals 112 the special tool 116 is
used. This is screwed into the seal 112, which can then be
pulled out (see Fig. 20A).
When the special tool 116 is screwed into the piston seal 112 the
latter is completely destroyed!
If you use only aqueous eluents the 6.2741.000 Piston seal can be
replaced by the 6.2741.010 PE Piston seal available as an option.