Isolation Valve Operating Order; Principle Of Operation - Systech Instruments EC900 series Operator's Instruction Manual

WARRANTY EXCLUSION
In some instances cells do not achieve their expected lifetime, failing early due to misuse: isolation
valves on the analyser left open causing ingress of high oxygen levels, or cell rupture caused high
pressure being applied across the cell. Misuse of the measuring cell in this way is not covered by the
warranty.
3.2 Measuring Cells Warranty - continued
NOTE
Most cells that do not last their expected lifetime fail because:-
1. The isolation valves on the analyzer are left open, causing ingress of high ambient
oxygen levels.
2. The cell has been ruptured caused by high pressure, usually caused by the isolation
valves being operated in the wrong order. Ruptured cells can be confirmed by
electrolyte solution seeping from the inlet/outlet pipes or by blackening of the same
pipes.
4.0

ISOLATION VALVE OPERATING ORDER.

For analyzers sampling from pressurised supplies:
When opening the cell, open the OUT valve first, followed by the IN valve
When closing, close the IN valve first, followed by the OUT valve.
For analyzer fitted with a pump:
When opening the cell, open the IN valve first, followed by the OUT valve
When closing, close the OUT valve first, followed by the IN valve.
MISUSE OF THE CELL IS NOT COVERED BY WARRANTY
5.0

PRINCIPLE OF OPERATION

The detector contains an anode, electrolyte and an air cathode to which the diffusion of Oxygen is
limited by a diffusion barrier. At the air cathode Oxygen is reduced to Hydroxyl ions which in turn
oxidise the metal anode.
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EC900 Series Operation Manual
The following reaction takes place at the cathode:
O + 4e  4(OH)-
O + 2H
2 2
and at anode
2Pb + 4(OH)-  2Pb(OH)
and the complete chemical reaction is represented by
2Pb + O + 2H
2 2
+ 4e
2
O  2Pb(OH)
2
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