Metrohm 757 VA Computrace User Manual

Page 37

3.3 Multi-mode electrode (MME)

757 VA Computrace – Hardware

6 Replace sealing needle 76 if need be

If problems with leaks arise owing to a worn, deformed or damaged sealing

needle 76, this must be replaced. Three spare needles are supplied sepa-

rately in a protective plastic package. After unpacking a needle, please avoid

any contact whatsoever with the needle tip. The spare needle 76 is installed

as follows:
• Carefully pull old sealing needle 76 out of PTFE membrane of the slotted

screw 75.

• Carefully insert new sealing needle 76 without tilting into the hole in the

PTFE membrane of the slotted screw 75.

When the sealing needle

is changed, it is always necessary to

change the glass capillary

7 Replace sealing ring 85 if need be

• If the sealing ring 85 is contaminated or damaged in any way, it must be

replaced for the subsequent assembly of the MME. Two new sealing

rings 85 are enclosed in the package with the 6.1226.030 glass capillar-

ies.

8 Reassemble MME

• Screw slotted screw 80 using a suitable coin flush into screw thread 79.

Do not turn so tightly that the cemented-in steel threaded ring

becomes loose and hence jeopardizes the tightness and safety of the

MME!

• Using a suitable coin, screw slotted screw 75 into the screw thread 77

until the contact surface of the black O-ring at the Plexiglas wall (thin,

black stripe) is just visible below the metal thread 77.

• Place multi-mode electrode 17 with the opening 83 facing upwards in the

electrode holder 93 (see Fig. 11-1).

• Insert insert ring 84 in opening 83.
• Push sealing ring 85 onto locking ring 86 and insert both in the opening

83.

• Screw retaining nut 87 by hand into screw thread 83 until a slight resis-

tance is felt.

9 Add mercury

Proceed as described in section 3.3.2.

10 Mount new capillary

Proceed as described in section 3.3.3.

11 Fill capillary

Proceed as described in section 3.3.4 or section 3.3.5.