ML488 | v19
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Expo Technologies UK
T: +44 (0) 20 8398 8011
E: [email protected]
Expo Technologies US
T: +1 (440) 247 5314
E:[email protected]
Expo Technologies China
T: +86 532 8906 9858
E: [email protected]
Purge Flow Sensor
The Purge Flow Sensor monitors flow through the Purge Outlet Valve. At correct purge flow rates, above the
minimum specified for purging, the sensor sends a signal that activates the purge timer. This sensor is factory
calibrated to operate on falling flow rate at or above the minimum specified purge flow rate.
CLAPS Sensor
This sensor monitors the pressure within the pressurized enclosure and sends a control signal to the CLAPS
Regulator. The normal running pressure must be determined prior to system start-up so that the CLAPS Sensor
may be set to the level required to control the CLAPS Regulator.
Electronic Purge Timer
When both the enclosure pressure and the purge flow rate are correct, the Purge Flow Sensor activates the
timer and the electronic timer starts. The timing period is selected using switches mounted on the timer
module.
Note: Setting the timer to 00 minutes will cause infinite purging; the cycle will never complete.
During timing, the percentage of the purge cycle is indicated by four LEDs which flashes sequentially while
the timer is running.
The Electronic Timer contains an intrinsically safe battery pack that needs regular replacement. See
Commissioning section
Alarm Only Circuit (/AO)
If the pressure in the pressurized enclosure is too low the system will normally cut off electrical power to it. In
certain circumstances, where local codes of practice allow, the system can be altered to provide a hold-on
circuit that will maintain the electrical power supply to the pressurized enclosure while also providing a
pressure failure alarm. The user must respond to the alarm and either restore the pressure to the pressurized
enclosure or otherwise make the installation safe; for example, cut off the electrical supply. The decision to
use the Alarm Only facility, and the allowable length of time for non-pressurized operation, is the responsibility
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.
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.
LED 1
LED 2
LED 3
LED 4
LED 1
LED 2
LED 3
LED 4
LED 1
LED 2
LED 3
LED 4
LED 1
LED 2
LED 3
LED 4
0 to 25%
of purge time
26 to 50%
of purge time
51 to 75%
of purge time
76 to 100%
of purge time
