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ML488 | v19
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
System Purging Switch (Optional)
This switch is operated by the purge flow signal that allows a remote electrical system status indicator to
signal that the system is purging; sometimes referred to as “purge-in-progress”. The cable from the switch is
terminated in the /PA terminal box.
Intermediate Switch
This is a flameproof switch which is activated by the signal from the Intermediate Sensor. The cable from the
switch is terminated in the /PA terminal box.
Visual Indicators
Visual indicators are fitted to provide status information to the operator.
* The Green
/ Black
combination indicates normal operation of the pressurized enclosure after the
initial purging cycle has been completed.
Relief Valve Unit
The Relief Valve Unit allows the purge air to exit the enclosure safely via a built-in spark arrestor. This spark
arrestor is designed to prevent the emission of arcs, sparks and incandescent particles produced within the
pressurized enclosure.
Purge air passes through the Relief Valve Unit; the preset pressure differential across the appropriate orifice
ensures that the purge flow sensor is activated once the selected purge flow has been attained.
During the purge cycle a pneumatic cylinder operates the Purge Outlet Valve that lets the air from inside the
enclosure exhaust through the Relief Valve Unit. When the system changes to leakage compensation mode,
the Purge Outlet Valve is closed and the enclosure sealed.
The Relief Valve Unit has an in-built relief valve. This is sized to ensure that, if the air supply pressure rises up
from the specified maximum, the internal enclosure pressure will not exceed the specified maximum working
pressure of the pressurized enclosure.
/PA Terminal Box
The Terminal Box is increased safety (Ex e) certified and incorporates the terminal connection points for the
alarm and interlock switches. All contacts provided are volt free (dry).
Cable entry methods (for example conduit or cable glands) must also be certified to IECEx, ATEX and/or
INMETRO standards (and must match the certification scheme for the motor). The main requirement is that
IP66 (or better) ingress protection must be provided by use of seals or washers.
Alarm / Pressurized Indicator
Green* Pressurized
Red
Pressure Alarm (enclosure pressure low)
System Purging Indicator
Black*
Purge flow too low (not in purge mode)
Yellow (flashing)
Purging (flow above minimum)
