Pepperl+Fuchs 7500 User Manual page 54

7500 S M  P
erieS anual
Below is an equation for determining the purging time:
(number of volume exchange) x (volume of the enclosure) / flow rate = purging time
The number of volume exchange depends on
the item being purged and
the standard it is being evaluated to.
Number of exchanges
4
5
10 (motors)
EXAMPLE
P3=
Vent=
Enclosure volume=
Flow rate from P3=
(see table)
NFPA
(Class/Division)
Zone (ATEX, IECEx)
NFPA:
Zone:
Motors:
The 7500 control unit has a purge timer and is user-selectable through the menu.
The purge timer is activated when the enclosure pressure goes above P3. The
pressure must always be above P3 for the timer to continue until it counts down to
000:00. If the enclosure pressure drops below P3 for any amount of time, then the
timer is reset to its starting value and will not start counting down until pressure is
above P3.
The flow rate for P3 value can be found on the graphs for vent flow in Section 2.4.2.
The flow rate for P3 depends on the EPV-7500 vent that is being used.
The more the enclosure leaks pressure, the higher the flow rate into the enclosure
required to achieve the P3 threshold.
54
rograMMing
Class/Division (NFPA 496)
X
n/a
X
2.6 inches water
EPV-7500-...-02
table for P3: EPV-7500-...-02,
see Section 2.4.2
10 ft³
11.3 scfm
4 volume exchange
5 volume exchange
4 x 10 ft³ / 11.3 scfm = 3.6 min
5 x 10 ft³ / 11.3 scfm = 4.5 min
10 x 10 ft³ / 11.3 scfm = 8.9 min
Zone (60079-2)
n/a
X
X
6.5 mbar
282 liters
320 liters/min
4 volume exchange
5 volume exchange
4 x 282 liters / 320 l/min =
3.6 min
5 x 282 liters / 320 l/min =
4.5 min
10 x 282 liters / 320 l/min =
8.9 min