OPERATING PROCEDURES - continued.
c. Monitoring Differential Pressure (DP).
(Refer to Figure 2-17). The DP gage (1) indicates the differential pressure
between the inlet and out pressures to determine filter element condition Differential pressure is checked by observing
the needle indication on the DP gage (1). When the reading reaches the yellow zone, the filter elements of the first stage
filter should be replaced immediately after operation. If reading in the RED PORTION, STOP IMMEDIATELY AND
NOTIFY UNIT MAINENANCE
During operation at subfreezing temperatures, below 32°F, filter elements can accumulate ice
crystals, causing an increase in the DP gage reading. Allow the fuel system to operate, circulating
fuel for a period of time while observing the DP gage. If the gage indication remains in the yellow
zone, filter plugging is by solid contaminants. Notify unit maintenance that replacement of the
elements is required.
d. Air Purging. (Refer to Figure 2-17). Purging air from the filter-separator tank is necessary when filling tank,
refer to para 2-5.
Place an empty container under the air vent tube assembly (2).
Slowly open the air vent valve (3) and allow air to escape from the vent tube assembly (2)
Close the air vent valve (3) when fuels flows out of the vent tube assembly (2).
For disposal of contaminated fuel, refer to FM 10-20.
Figure 2-17. Air Purging.