SICK GM35

94
8009441/YN36/V3-0/2015-08| SICKOPERATING INSTRUCTIONS|GM35
Subject to change without notice
MAINTENANCE
8.4 Maintenance work on the purge air supply
Hot gases in ambient conditions with overpressure
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:
– If the sample gas duct contains a partial vacuum that is sufficient to flush it adequately
with ambient air when the purge air supply is removed, the SR-unit and reflector can
remain inside the duct while maintenance is being done on the purge air unit.
– 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 reflector. In addition, the purge air hose should also be disconnected during purge
air fixture maintenance as described below.
8.4.1 Preparation and general inspection
▸ With the purge air unit switched on, remove the purge air hose from the purge air inlet
on the respective purge air fixture.
▸ 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.
▸ Remove the weatherproof cover, if fitted, from the purge air unit.
▸ 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.
▸ Make sure cables are not damaged along the whole length and connections are not
loose, and check cables for corrosion and humidity. Repair accordingly when necessary.
▸ Check the purge air hose carefully for damage. Pay special attention to points subjected
to mechanical strain, such as on the hose clamps.
▸ Check all the remaining hose clamps on the purge air hose and purge air unit to ensure
that these are secure; tighten when necessary.
▸ Make sure the dummy plug for the Y-distributor on the purge air unit is secure.
WARNING: Risk of fire through hot gas escaping in installations with over-
pressure 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.