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ML442 | v5k
Expo Technologies UK
T: +44 (0) 20 8398 8011
Expo Technologies US
T: +1 (440) 247 5314
Expo Technologies China
T: +86 532 8906 9858
In Leakage Compensation
(LC)
systems a dedicated Purge Flow Sensor measures the
differential pressure between the "DP HI (High) / Enclosure Pressure" and the pressure in the
monitoring device at the back of the RLV "DP LO (Low) RLV Connection". This connection
requires a pipe to connect the CU to the RLV25.
4.7 Power Supplies and their Isolation
All power entering the PE shall be provided with a means of isolation. This requirement also
applies to any external power sources, which are connected to equipment such as "volt-free" or
"dry" contacts within the PE. Printer signal, network cards, etc need isolation.
Exception:
Power to other apparatus that is already suitable for the hazardous area need not to
be isolated by the MiniPurge
system.
In all cases the application and the isolation of the power must be controlled by the MiniPurge
system. Refer to Specification Sheet for output options available.
4.8 Adjustments and Settings
Purge Time
If no specific purge test has been performed on the PE, the volume of the PE must be
determined by the manufacturer or user and the necessary purging time calculated based on
the purge flow rate specified by the “standard” being used. It is the user's responsibility to verify
or enter this data on the PE and/or MiniPurge
system nameplate. Ask Expo if in doubt. The
IEC / EN 60079-2 permits 5 free volume changes and an example of the calculations is as
follows:
If the PE external dimensions indicate an internal free volume of 500 Litres then,
500 litres enclosure volume x 5 volume changes = 12 minutes purge time
225 litres/minute purge flow rate
If the PE is a motor, experience of purge testing shows that it is prudent to multiply the
motor internal "free” volume by ten to get the purging volume.
500 litres enclosure volume x 10 volume changes = 23 minutes purge time
225 litres/minute purge flow rate
The following applies for NFPA 496 standards where 4 complete volume changes are permitted
for enclosures except when the PE contains a motor when 10 volume changes are required.
If the PE external dimensions indicate a total volume of 8 cubic foot, then,
8 cubic foot enclosure volume x 4 volume changes = 4 minutes purge time
8 cubic foot/minute purge flow rate, (see above)
If the same PE contains a motor, then,
8 cubic foot enclosure volume x 10 volume changes = 10 minutes purge time
8 cubic foot/minute purge flow rate, (see above)
The standard MiniPurge
units have the patented digital
pneumatic timer system as shown in
Figure 9
MiniPurge
timer block
. The purge time is set by
opening / closing the pinch valve so that the sum of the
open valve times equals or exceeds the required purge
time.
At least one valve must always be open, and
the screws must be at the appropriate limit of travel.
Do not over tighten.
Figure 9 MiniPurge
timer block
