VAF instruments OILCON MARK 6M - Miscellaneous; Oil Content Reading Higher than Expected; Oil Level Alarm

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7.4 MISCELLANEOUS
This section is to describe problems that may be encountered during operation and the possible
reasons.
7.4.1 Oil content reading higher than expected
During a normal discharge run of ballast water the ppm reading should be between 50 to 150 ppm
assuming that sufficient time has been left to allow the oil to settle out in the tank.
The reading should be steady for most of the duration of discharge. If the reading varies rapidly with
large deviations, it is likely that air is being entrained into the ballast water. This could be due to a
partly filled overboard line, a cavitating cargo pump or a low suction pressure on the monitor sample
pump casing causing air to enter the pump.
If the ppm reading is consistently high, press the FLUSH key. This will cause the monitor to run on
fresh water for a short time. During the flush the ppm reading should go down to zero.
NOTE:
Pressing the FLUSH key will signal the MCU to stop discharging overboard, since the
monitor is no longer sampling the ballast water.
Once the calibration check is completed the monitor will return to sampling the ballast water. If the
reading returns to its previous level, then it is sure that the reading is accurate.
If there is any further doubt, the only solution is to stop the monitor and restart it again thereby
forcing it to complete a full flushing cycle.
7.4.2 Oil level alarm
During a normal ballast discharge, the ppm reading should be quite low probably in the region of
between 50 and 150 ppm, as the main bulk of the ballast tank is decanted. During this time, the rate
of discharge in litres per nautical mile as calculated by the MCU, will also be steady and remain
within the permitted limits. Obviously, as the level in the tank drops, there comes a time when the
reading on the monitor will start to rise, as oil is stripped from the layer on the surface. It is difficult to
predict at what depth of water this will occur due to a number of reasons:
 how long the tank had been left to settle
 whether or not heating has been applied
 weather conditions during discharge
 type of oil being carried
However, it is true to say that the entering of oil into the ballast water occurs when an appreciable
level of separated water remains in the tank. The oil is pulled down from the oil-water interface due
to swirling in tanks, powerful cross currents between the frames and watering over frames. This is
all caused by a high rate of pumping. To reduce this effect and to allow a greater quantity of water to
be pumped out, the rate of pumping must be reduced. This will have the effect of reducing the
amount of oil entrained, and the ppm reading should therefore fall.
In this way, the monitor can be used as an accurate means of sensing the oil-water interface and
ensuring that the maximum amount of water is discharged. If the “oil level” alarm should sound,
reduce the pumping rate until the ppm reading falls and becomes steady. After a time the reading
will rise again. Reduce the pumping rate further to let the ppm reading fall again. Repeat this cycle
until the pumping reaches the oil-water interface at which time the ppm reading will rise rapidly and
go over scale. The discharge will now be complete. Considerably more water will have been
discharged using this technique, although it will have increased the time needed to discharge the
ballast water.