TM 10-4930-351-14
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OPERATING PROCEDURES (Continued)
c.
Rating Procedure
(1) Disconnect the monitor housing bypass line (figure 8, 12) from the valve body (13).
(2) Remove the monitor (11) from the monitor housing (10).
(3) Using tweezers (figure 7, 12), remove the test pad (14) from the monitor (13).
(4) Press the test pad (14) between dry paper blotters or absorbent towels to remove excess fuel. To blot, press
firmly (about 5 lbs of force) three or four times with the heel of the hand, moving the pad with tweezers (12).
NOTE
The test pad should be read within three minutes after sampling is initiated. If the test pad
is not read immediately after sampling, it must be placed in a desiccator to prevent
moisture pickup from the air. Ratings made on dried test pads, not damp with fuel,
should be avoided as they will give high and erroneous readings. In addition, rating a pad
which has not been well blotted will give a low reading as the excess fuel will absorb
part of the UV light and decrease fluorescence.
(5) Using tweezers (12), remove the calibration standard under the water detector window (figure 8, 2). DO NOT
DISCARD the calibration standard.
(6) Using tweezers (figure 7, 12), put the test pad (14) under the water detector window (figure 8, 2). Place the
power selector (3) to the appropriate power source.
(7) Press and hold the light button (5) located on the back side of the instrument pack (6). The ultra violet light
must be on to get a reading. This can be checked by moving the light modulating lever (4) on the water detector
(1) from one extreme to another. The instrument pack indicator needle (7) should swing violently when the
light modulating lever (4) is moved.
(8) Zero the water detector (1) by adjusting the light modulating lever (4) until there is a steady reading for 10 to
15 seconds. Always move the light modulating lever (4) in the same direction when zeroing the water detector
(1) to eliminate errors caused by backlash. Release the light button (5) on the instrument pack (6) when the
reading is complete.
(9) Observe the light modulating lever (4) and corresponding number. Record the instrument reading (estimate to
the nearest tenth) and the sample volume.
(10) Set the water detector power selector (3) to OFF to conserve power.
(11) Record the temperature of the fuel.
(12) Using tweezers (figure 7, 12), remove the test pad (14) from the water detector (8) assembly for visual
observation. Free water in fuel is normally well dispersed and will form an even distribution of many, small
points of yellow fluorescence on the test pad when illuminated by ultra violet light. Large drops of water will
form a few large spots of yellow fluorescence on the pad. The large spots may give erroneous readings, and
should be disregarded and a new sample taken.
d.
Calculations
The instrumentation reads directly, IF the sample volume is 500 ml. Correct the readings for other size samples by
multiplying reading by 500/sample size in milliliters:
Free water, ppm = (meter reading, ppm) (500) / (sample volume, ml)
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