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7500 Series Manual
3 General Information on Purge and Pressurization
Purge and pressurization is one of the most versatile ignition protection classes. Purge and pressurization
systems are based on the principle that in Zone 2/Class I Division 2 (gas), the gas mixture in the ambient
atmosphere, which may ignite under certain circumstances, is removed from the housing by an initial purge
process. After the purge phase, sufficiently compressed inert gas, usually air, is supplied to compensate
for leaks in the housing and any installed equipment. This permanent overpressure prevents any potentially
explosive atmosphere in the ambient air from entering the housing. During the purge phase, an internal
pressure is achieved.
For applications in Zone 22/Class II Division 2 (dust), the purge process is omitted because purging would
raise explosive dust into a cloud, creating a possible hazard. Instead of pre-purging, the interior of the
housing is inspected for dust and cleaned manually if dust is present.
Purge and pressurization systems are particularly suitable for installed equipment that is not approved for use
in hazardous areas. The equipment can then be used directly in the hazardous area.
3.1 Conditions of Safe Use
1. The main control unit and the EPV vent are the only parts that have been evaluated for the system’s
certifications.
2. All unused entry points to the 7500 control unit shall be closed with a properly certified IECEx, ATEX,
or cULus device that is suitable for the installation location and has the necessary ingress protection.
3. For dust environments, the non-metallic window may pose an electrostatic discharge hazard. To clean
the device, use only a water-damp cloth and allow to air dry. Do not use or install in high charge-
areas. See IEC60079-32-1 for more information.
4. When the 7500 series purge and pressurization system is mounted to an enclosure, the complete
installation shall be evaluated to the appropriate standards and regulations that are applicable for
the final installation location. These include, but are not limited to NFPA 496, IEC 60079-2, and IEC
60079-14. These standards shall be available at the site of installation. See certificates for applicable
editions.
5. The purge control unit has a temperature class (T6, T5 or T4) that is dependent on ambient
temperature. This temperature shall be considered when mounted to an enclosure, or inside of an
enclosure. See details on the certificate.
6. The bypass function shall only be enabled when the area is known to be non-hazardous.
7. In a hazardous dust environment, regularly remove dust from the unit to prevent excessive
temperature rise. See certificate for full information.
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