Purging Timer; Determining Purge Time - Pepperl+Fuchs 7500 User Manual

4.5. Purging Timer

4.5.1

Determining Purge Time

Programming the Purging Timer (MIN:SEC)
1.
Calculate the purging time using the formulas and examples in Chapter 4.
2.
Enter the purging time using the UP and DOWN buttons and SET.
3.
To change the purging time by 1-second increments, press the UP or DOWN button.
4.
To make purging time faster, hold down the button continuously. Purging time will
advance faster, as the button is held down for longer times (in 5 seconds, 1 min, 5 min
increments).
Maximum purge time is 254:59.
To make sure the enclosure is safe from the hazardous atmosphere, the inside of the
enclosure has to be free of the hazardous atmosphere and pressurized before the
equipment inside can be powered.
The first step in this process is to get rid of the hazardous atmosphere within the
enclosure.
For a dust atmosphere, the inside of the enclosure must be cleaned out and then
pressurized. Because most vents on a pressurized enclosure have a spark arrestor,
purging is not the method used. The dust must be cleaned out manually or with
a vacuum that is rated for the area. Alternatively, it must be cleaned out in a non-
hazardous area.
For gas atmospheres, the enclosure is purged by introducing a flow of protective
gas (compressed air, or Inert gas) through the enclosure to make it safe. Depending
on the standards that are being used to evaluate the effectiveness of the purging
operation, the volume of protective gas through the enclosure determines the amount
of time for purging. The exchange of protective gas is related to the volume of the
enclosure, the number of exchanges, and the flow rate through the enclosure.
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