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Model 9017 Y/Z-Purge Operator Interface
2 Hazardous Area Safety Methods: Theory of Operation
2.1 Division 1: Y/Z-Purge Protection
The Z-Purge (Model 9017) and the Y-Purge (DAISY Enclosure Mounted) Systems are
Electrically and Pneumatically the same. For the rest of this manual they will refer to
as a Z-Purge. The I033-000002-03 Printed Circuit Board will be called the ZPA
Assembly.
Z-purge systems are used for installing electrical equipment in hazardous areas (see
National Electrical Code articles 500-504 and the NFPA 496, section 2-8).
A Z-purge system provides the protective purge and maintenance of safe gas flow to
the enclosure; the purge system operation and the power and signal connections are
controlled by the operator (as opposed to the automatic control provided by X-purge
systems Model 9016). The purge system includes alarm contacts and a visible
indicator to alert the user and possibly an automated control system in the event of
the loss of pressure within the enclosure; that is, a failure of the protective safe gas
flow or of enclosure integrity.
At start-up, the enclosure is purged of any possible flammable materials by applying a
rapid flow of air through the enclosure. Prior standards simply required an exchange
of four volumes of air through the enclosure. However, the standards now require
that the volume of air passed through a given enclosure eliminate any possible
flammable concentration of substances within the enclosure (the minimum of four
volumes of exchange still applies). Factory Mutual Class Number 3620 (section 4.2,
page 5) states, "When ... concern exists that all compartments may not be purged,
purging tests shall be conducted." This requires consideration not only of the airflow
and pressure, but also of the enclosure's shape and the effect of equipment installed
within the enclosure. DAISY's systems have been fully tested under the supervision of
Factory Mutual to ensure compliance with the standards of FM 3620: 4.2.
After the enclosure has been purged, the operator switches the purge control to the
"operate" setting. At this setting, the air flow rate is reduced to conserve the
protective gas while still maintaining a positive pressure within the enclosure to
prevent the entry of flammable materials. At this time, the operator can apply power
to the electronics within the enclosure. In the event of a loss of protective pressure
within the enclosure, the alarm system will indicate the failure. The operator must
then shut off power and signal connections at a safe disconnect location.
Y-purge systems are used for installing electrical equipment in Division 1 hazardous
areas (see National Electrical Code articles 500-504 and the NFPA 496, section 2-9).
Essentially, the installation of a Y-purge on a DAISY enclosure in a Division 1 area
reduces the rating inside of the enclosure to Division 2. This allows less costly Division
2 electronic equipment to be safely used in Division 1 areas.
February 2022
2
Daisy Data Displays, Inc.
D011-000002
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