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6.4
System “Z” Purge Instructions for All Systems
A 3 inch diameter threaded pipe connection is provided to receive an air or nitrogen supply,
a 90 cfm blower is recommended. This blower shall not be installed or placed in the
hazardous environment where hazardous fumes will be drawn from for supply air to the
electrical enclosure or internal cabinetry of the Mokon system. The optimum nitrogen or air
supply range to the Mokon system should be .15 to .5 inches of water column.
As an alternative to nitrogen, non-hazardous “clean” dry air can be supplied which can also
include clean dry compressed shop air.
The discharge pressure of the fan or blower needs to be, at least, 3.0 inches of water
column for every 100 equivalent feet of 3” duct. For 4” duct, 1.0 inch of water column per
100 feet is adequate. A 3” exhaust connection is also provided.
Note: Due to temperature considerations, the purge gas must flow (sweep)
through the unit to insure adequate ventilation.
Once the purge gas is introduced, the Dwyer model 1950-0-2F pressure switch will close,
energizing a time delay relay. The relay prevents start-up of the Mokon system until an
adequate sweep inside the unit has taken place. The switch is set at its minimum setting of
0.15 inches of water. A green pilot light will illuminate once the relay has “timed out”,
indicating it is safe to operate the unit.
The magnehelic gauge has a scale of 0 to .5 inches of water, and is clearly visible to allow
the operator to monitor the unit.
If the purge is lost, for any reason, the pressure switch will open, thus activating a customer
supplied alarm through a set of auxiliary contacts. The Mokon system will also shut off.
For systems that are classified and applied properly the applicable Class, Group and Division
is listed on the bottom of the systems serial tag.
Methods: There are typically two methods for the supply of purge gas to systems for “Z”
purge applications, they are as follows:
Method # 1 (recommended): Due to temperature considerations, the purge gas must
flow (sweep) through the unit to insure adequate ventilation. This method would apply
to water, oil, chiller, and full range heater/chiller systems.
Method # 2: (not recommended): Pressurization of the cabinetry when temperature
build up is not as much of a concern can be applied. Here the exhaust coupling on the
cabinet would be plugged. This method would apply to water-cooled chiller systems or
very low heating capacity systems.
Note: If the “Z” purge mechanism or any other system safety devices are modified
or disable in any way Mokon considers them to be non-operational and the
systems warranty could be void.
