0003 00
TM 55-1925-285-13&P
backflush modes. Oil droplets that flow past the inlet baffle accumulate on the polypropylene granules (beads) in
the coalescer, which have 10-mesh screen tops and bottoms to hold the raw polypropylene granules. The
polypropylene granules attract oil and repel water (oleophylic-hydrophoic), allowing water to flow through, while
the oil remains temporarily trapped in the coalescer granules. As the accumulated oil droplets combine and grow
in size (coalesce), they become more buoyant, then break away and rise to the top of the tank. The lower
coalescer bed functions like the upper one, but is thinner and acts like a polishing bed. The water space between
these beds isolates them, preventing contamination of the lower by the upper. The clarified effluent, having
passed through both coalescer beds, is drawn through the outlet in the tank bottom (figure 1, item 5) and piped
overboard or recirculated back to the OWT. The destination of the discharge is controlled by the OCM, whose
theory of operation is detailed later in this work package.
FACTORS AFFECTING OWS OPERATION
Several factors can have an undesirable effect on OWS operation. Among these factors are emulsified oil,
vacuum leaks, and synthetic oil. The effects of each of these factors are explained in the paragraphs below.
EMULSIFIED OIL
The OWS is not designed to separate emulsified oil/water mixtures (mixtures where the oil droplets are thor-
oughly mixed with the water and are too small to be removed by the coalescer beads). Emulsions can be formed
by mechanical agitation or by the addition of emulsifying agents, such as solvents or detergents, to the mixture.
To ensure proper operation of the OWS, it is important to keep all such chemicals out of the bilges to the greatest
extent possible. One way to do this is to use only short-lived detergents for bilge cleaning or for other operations
when cleaning water will enter the bilge area. Table 1 lists two such detergents.
Table 1. Approved Short-Lived Detergents for Bilge Cleaning
Detergent/Quantity
NSN
Allied P-98 by Allied Enterprises
55 gallon drum .................................................................................................... 6850-01-278-4420
30 gallon drum .................................................................................................... 6850-01-278-3858
5 gallon bucket ................................................................................................... 6850-01-278-4421
55 gallon drum .................................................................................................... 7930-00-282-9700
5 gallon bucket ................................................................................................... 7930-00-985-6911
1 gallon container ............................................................................................... 7930-00-282-9699
VACUUM LEAKS
The OWS pump is located on the outlet side of the OWS tank to prevent the emulsification of the oil/water
mixture that would occur if the pump were on the inlet side of the tank. The OWS tank and inlet piping are thus
under a vacuum, which is measured by the compound pressure/vacuum gauge on the tank top. Depending on
the suction lift required, this vacuum will vary. The pump has a 25-foot (7.6 m) vertical lift capability, but a 15-foot
(4.6 m) maximum vertical lift is recommended. The vacuum gauge reading should be recorded at startup and
referenced as necessary to determine if the inlet basket strainer needs cleaning or if the inlet piping has become
clogged. It is important that the inlet piping is tight and leak free (bubble tight under vacuum) to minimize the
amount of air the system will process. Since the conductivity type interface sensor cannot distinguish between air
and oil, air entering the separator tank can cause the OWS to perform excessively frequent oil discharge cycles.
SYNTHETIC OIL
Since the OWS relies on specific gravity differences between oil and water to separate them, synthetic oils or
hydrocarbon sludge heavier than water will not be separated by this unit, and can result in fouled coalescers and
piping. Oils with a specific gravity of 0.96 and less can be processed by this unit at its rated flow. Any oils with
higher specific gravities should be segregated at their sources, and not allowed into the bilges.
0003 00-2