Appendix F: The X-Purge System; Description - Thermo Scientific SOLA II Flare User Manual

Appendix F: The X-Purge System

Description

The optional X-Purge assembly is used to provide safe operation of analyzer
systems in Class 1, Division 1, Groups B, C, and D (NFPA) and Zone 1, Ex
d[p] IIC T4 (ATEX and IECEx) hazardous areas. Safe operation is achieved by
automatically disconnecting power from the analyzer system if the purge
pressure is lost in any of the monitored enclosures or if purge flow out of either
enclosure exhaust port is lost. The X-Purge system also ensures that the system
is safe before it permits power to be applied to the analyzer system. To ensure
continued safe operation of the analyzer system, the X-Purge unit must not be
disabled or adjusted improperly.
On power-up, the X-Purge system checks the purge pressure in all monitored
enclosures and for flow exiting the exhaust ports of the enclosures. When all
monitored enclosures register pressures at least
0.3 inch of water (0.75 mbar) above the reference pressure, adequate flow is
present at the enclosure exhaust ports, and the instrument air pressure is greater
than 10 psig, a time delay relay begins its timed cycle. Typically, the time delay
is used to ensure that at least four volumes of air are exchanged in the
enclosures before power is applied to the system. (The number of exchanged
volumes may be higher in some situations.) After the preset time delay is
accomplished, the time delay relay applies power to the analyzer system.
Typically, the X-Purge assembly is designed for monitoring two enclosure
purge pressures and two exhaust port flows. All of the pressures in the
monitored enclosures must be at least 0.3 inch of water (0.75 mbar) higher
than the atmospheric pressure around the analyzer system. This ensures that
hazardous materials are less likely to leak into the purged enclosures.
Pressure differential switches compare the pressure in the monitored enclosures
with the pressure in the explosion proof X-Purge enclosure. The inside of the
X-Purge enclosure is referenced to ambient pressure using a 1/4-inch breather
drain with flame suppression. A flame arrestor is also installed between each
pressure differential switch and the associated pressure enclosure that it
monitors. A spark arrestor vent is used for exhaust purposes and to maintain
appropriate backpressure on the electronic enclosure and oven.
Thermo Scientific SOLA II Flare User Manual F-1