MIL-HDBK-1027/1B
Bronze bearings should not be used in high temperature dampers.
Bronze bearings have a maximum temperature rating of
149 degrees C. Other bearing materials which should not be used
in high temperature dampers are: nylon, Teflon, and stainless
steel. The following bearing is acceptable for use with
538 degrees C high temperature dampers:
MATERIAL
BEARING TYPE
MAXIMUM TEMPERATURE
RATING DEGREES C
Carbon and/
or Graphite
Sleeve
538
e) Dampers should be electrically operated and should
be installed in the exhaust ductwork outside of the training
compartment. Damper actuators for high temperature dampers
should be accessible for maintenance.
f) Dampers should have a quick opening and closing
time. The maximum time of operation of the dampers from any
position to another position should be 15 seconds.
3.11.6.3 Fan. The exhaust system for each building should be
sized to pull approximately two times the "air in" rate due to
volumetric expansion of the heated air. These values are listed
in Table 1 entitled "Main Ventilation Air for Fireplace
Compartment" for each structure. Design temperature for flow
calculations should be 315.5 degrees C. The design temperature
for materials should be 538 degrees C. The fan and the exhaust
system should meet the following criteria:
a) The exhaust system should consist of at least two
fans totaling 100 percent of the ventilation requirement. The
exhaust system should be designed for operation at 538 degrees C
and should be provided with high temperature expansion joints
suitable for operation at 538 degrees C in lieu of flexible duct
connectors. The exhaust system ductwork should be constructed
of low carbon stainless steel, 304L or 316L. Carbon steel
should not be used because of high temperatures; the corrosion
rate is increased and its structural strength is reduced due to
the segregation of carbon. Ductwork design pressure should be
noted on the drawing and should be based on the addition of the
following:
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