in the last couple of months, two topics concerning the sampling line of the OWS emerged from PSC inspections which led to some interesting publications from Class societies:
The OWS does not stop or does not re-direct the effluent via the 3-way valve from ovb’d to the bilge holding tank, when the sampling line is closed/blocked.
There were some reports that the above scenario, concerned only some systems manufactured by JOWA, truth is we have seen a similar behavior also with systems from major Japanese vendors equipped with the Bilgemon488 but supplied without a pressure switch in the ppm unit.
In case the sampling piping is equipped with a valve, it is suggested this valve to be removed or to be sealed in the open position (and same to be written in the oil record book).
The sampling point on the ovb’d line is not located in a vertical section of the piping and/or it is located far from the equipment outlet.
This one has to do with the assumption that the sample taken, may not be representative if the sample point is in a horizontal position, as due to the density difference of oil & water, the effluent stream driven to the ppm unit may consists only of water.
For more information please refer to the attached publications from ABS & DNV.
Remember that for any modifications on the OWS piping, you should have the confirmation from Class first.