Installation And Operation; For Gas Atmospheres - Pepperl+Fuchs 7500 User Manual

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3. Installation and Operation

The 7500 series control unit, vent, and manifold can be universally mounted to the
customer enclosure. The 7500-01-AA-STD-UNV-PNO is panel-mounted to the
enclosure. An included bracket provides a Type 4X / IPX66 mounting. The 7500-MTD-
PM... includes the 7500-01... control unit and 7500-MAN-MV-01 mounted onto a
flat panel that is then panel-mounted to the enclosure with the included bracket and
gasket for a Type 4X / IPX66 mounting. The 7500-MTD-BX... includes the 7500-01..
control unit and 7500-MAN-MV-01 mounted onto an enclosure that can then mount
externally to the main enclosure. The EPV-7500 vent can be externally or internally
mounted with just the cap showing for exhausting the pressure.
The 7500 system is designed to allow the enclosure to be located in Zone 2 or 22,
Class I or II, Division 2 hazardous locations to operate safely by first making them
safe internally. This is done either by purging out the hazardous gas or by manually
cleaning out the dust hazard and then pressurizing the enclosure so that the internal
pressure prevents the hazardous atmosphere from entering. The 7500 control unit
has a differential pressure sensor within the unit that is pneumatically connected to
the protective enclosure to provide pressure for evaluation of the enclosure pressure
and the flow through the enclosure during purging. If pressure is lost, then power
can remain on. An indication by an alarm or display has to notify the operator of the
condition. If the pressurized enclosure has been opened or a positive pressure has
not been maintained, then purging for hazardous gas or cleaning the enclosure out
for dust atmospheres is required. The flow measurement is evaluated by using the
pressure in the enclosure and the known measured flow in the tables through one of
the vents selected.

3.1. For Gas Atmospheres

If the protective enclosure has been opened or has been subjected to the hazardous
atmosphere, purging is required to flush out the hazardous gas that may be inside
the protective enclosure. A protective gas is introduced into the enclosure so that the
pressure builds up and is exhausted through the enclosure. The measurement of flow
is achieved by the 7500 control unit pressure sensor measuring enclosure pressure
and using that pressure for the flow tables of the vent selected and enclosure size.
Each vent has an enclosure pressure vs. flow table for enclosure size that can be
used to determine flow rate. This flow rate is used to determine the purge time
required to make the protective enclosure safe.
Note
The flow rate tables generated for each vent are measured on a completely sealed
enclosure with no leakage from the enclosure. In real applications, there will be some
leakage from the enclosure, which will depend on the integrity of the seals and door
windows, etc. As the enclosure pressure increases, the leakage may also increase.
Always plan on more flow from the protective gas to achieve enclosure pressure
because of the leakage.
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