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8009389/YN39/V3-0/2015-08| SICKOPERATING INSTRUCTIONS|GM35
Subject to change without notice
MAINTENANCE
9.4 Maintenance work on the purge air supply
9.4.1 Safety
Hot gases in ambient conditions with overpressure
9.4.2 General information on maintenance work on the purge air supply
This Section is only applicable for devices with purge air supply, i.e. when a GMP measuring
probe is used.
The reliability of the purge air supply system is essential for ensuring the availability of the
measuring system. Maintenance of the purge air supply is straightforward, but should be
carried out extremely carefully.
Prerequisites for purge air supply maintenance:
– The measuring probe with the SR-unit is located outside the sample gas duct; if the duct
contains a partial vacuum that is sufficient to flush it adequately with ambient air when
the purge air supply is removed, the measuring probe can remain inside the sample gas
duct while the purge air unit is being maintained.
– The SR-unit is fully open on the flange fixture so that any dust blown through the purge
air hose during maintenance is not deposited on the optical interfaces of the SR-unit
and measuring probe. In addition, the purge air hose should also be disconnected from
the measuring probe during maintenance as described below.
9.4.3 Preparation and general inspection
1 With the purge air unit switched on, disconnect the purge air hose from the purge air
inlet of the measuring probe or optional pressure difference sensor to prevent any dust
that has been released during maintenance from being deposited on the optical
interfaces of the measuring probe and SR-unit.
2 Switch off the power supply (three phase) for the purge air unit and attach a suitable
warning to prevent it from being switched on again inadvertently during maintenance.
3 Remove the weatherproof cover, if fitted, from the purge air unit.
4 If there are noticeable external signs of contamination, clean the enclosure of the purge
air unit and, if possible, locate the cause of the contamination. The frequency with which
a filter change is necessary primarily depends on the dust content of the ambient air.
WARNING: Risk of fire due to hot gas escaping in installations with
overpressure conditions
On installations with overpressure, the purge air hose can be severely
damaged by escaping hot gas and can catch fire depending on the
temperature.
On plants with overpressure as well as gas temperatures over 200°C:
▸ Ensure reverse flow is prevented by fitting a (trip) flap or a valve.
▸ Regularly check the functionality of the reverse flow safeguard.
CAUTION: Device damage due to switching off the purge air unit too soon
When the purge air unit is switched off while the measuring probe is still in the
measuring duct, coarse contamination can reach and damage the SR-unit.
▸ Only switch off the purge air unit after the measuring probe has been
removed from the measuring duct.
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