Page
9
ML548_ES | v3
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
of the user.
Warning: It is potentially dangerous to energise the pressurized enclosure in an non-pressurized
condition when it is known that there is potentially explosive gas or dust in the hazardous location.
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.
Power Interlock Switch
This flameproof power switch is activated by the signal from the Purge Complete Valve. This activation can be
used to turn on the electrical supply to the pressurized enclosure. The cable from the switch is terminated in
the /PA terminal box.
Alarm / Pressurized Switch
This flameproof switch is operated by the pressurized signal. It allows a remote electrical system status
indicator to show either pressurized or a pressure failure alarm. The cable from the switch is terminated in the
/PA terminal box.
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.
High Pressure Switch (Optional)
This switch is operated by the signal from the High Pressure Sensor. It allows a remote electrical system status
indicator to show whether the pressure inside the enclosure has reached the pressure setting of the high
Pressure Sensor. The cable from the switch is terminated in the /PA terminal box.
Purge Valve
This changeover valve selects between purge air flow or leakage compensation. It is sized to allow sufficient
air into the enclosure during purging based on: the specified air supply pressure range, the minimum specified
purging outlet flow rate +10% and the expected leakage rate from the pressurized enclosure. At the end of
the purge cycle, the purge valve closes in response to the “Purge Complete” signal; it remains in the closed
position until the next purge cycle is initiated.
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)
