VAF instruments OILCON MARK 6M, Technical Manual

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ii) Starting interlock
The definition of a starting interlock is given in paragraph 3.4 of the Annex to IMO Resolution MEPC
108 (49) and is as follows:
“A starting interlock is a facility which prevents the initiation of the opening of the discharge valve or
the operation of other equivalent arrangements before the monitoring system is fully operational
when use of the monitoring system is required by the Convention.”
By its very nature Overboard Discharge Control can be considered a starting interlock, if the
overboard valves are controlled from the Main Control Unit. They will only receive a signal to open
for discharge when all the input parameters are correct.
If so connected as to stop the discharge by use of stopping the relevant pumps, this is not deemed
a starting interlock. In this instance a starting interlock could be typically a valve spindle brake.
For an example of an overboard control circuit by use of interlocking overboard and slop tank return
valves see drawing
0806-5019
. This also incorporates a starting interlock.
VAF Instruments advise that prior consultation is made with the classification society surveyor in
each case to ensure that the arrangement will be acceptable both as to the operation and with
regard to safety.
6.7.4 Pipework response time calculation
MARPOL regulations require that taking into consideration the length of sampling piping, the overall
response time is as short as possible between an alteration in the mixture being pumped and the
alteration in the meter reading and in any case not more than 40 seconds.
It is therefore, necessary to place a restriction on the length of the sample pipe from the probe to the
detector cell. The system response time specific for this installation can be calculated as follows:
Monitor response time
10.8
Total response time
40 sec
Sample response time
40 10.8 29.2
The maximum length of sample pipe (in this example the sample pipe outside diameter 15 mm and
thickness of the pipe 1 mm):
∙
∙
Where
sec
/