Time cycles vary for the purge and charge of night vision devices. TM 750-116 states
that maintenance personnel will purge and charge night vision devices every 90 days or when
condensation is evident in the device. The 90 day cycle does not apply to all night vision
devices. However, a visual inspection is required every 90 days for evidence of moisture.
Maintenance personnel will purge and charge night vision devices being repaired whenever the
repair function affects internal sealing.