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ML435 | v23
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
Intermediate Switch
This flameproof switch is used as simple apparatus for connection to intrinsically safe circuits only. It is activated
by the signal from the intermediate sensor. The cable from the switch is terminated in the Intrinsically Safe
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.
Purge Flow Restrictor
This valve restricts the purge flow to the minimum required flow rate. The Purge Flow Restrictor must be
readjusted during commissioning.
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.
CLAPS Regulator
This is the regulator that controls the leakage compensation air flow into the enclosure after the purging is
complete. It either increases or decreases the air flow into the enclosure as appropriate to maintain a stable
running pressure. The CLAPS Regulator must be set at the time of commissioning.
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.
Intrinsically Safe Terminal Box
The Terminal Box is for connection of Intrinsically Safe circuits only and incorporates the terminal connection
points for the alarm & interlock switches. All contacts provided are Volt free (dry). Cable entry methods (e.g. con-
duit or glands) shall conform to IEC / European or other relevant local codes and it is recommended to maintain
a minimum IP54 ingress protection.
