For maximum efficiency, you should operate purifiers at the maximum designed speed and rated capacity. Since reduction gear oils are usually contaminated with water condensation, the purifier bowls should be operated as separators and not as clarifiers.

When a purifier is operated as a separator, you should prime the bowl with fresh water before any oil is admitted into the purifier. The water seals the bowl and creates an initial equilibrium of liquid layers. If the bowl is not primed, the oil is lost through the water discharge port.

There are many factors that influence the time required for purification and the output of a purifier, such as the

1. viscosity of the oil,

Figure 10-36.-Tubular-type centrifugal purifier.

2. pressure applied to the oil,

3. size of the sediment particles,

4. difference in the specific gravity of the oil,

5. substances that contaminate the oil, and

6. tendency of the oil to emulsify.

The viscosity of the oil will determine the length of time required to purify the oil. The more viscous the oil, the longer the time will be to purify it to a given degree of purity. Heating decreases the viscosity of the oil, and this is one of the most effective methods to make purification easier.

Even though certain oils may be satisfactorily purified at operating temperatures, a greater degree of purification generally results if the oil is heated to a higher temperature. To do this, the oil is passed through a heater where the proper temperature is obtained before the oil enters the purifier bowl.

Oils used in naval ships maybe heated to specified temperatures without adverse effects. However, prolonged heating at higher temperatures is not recommended because of the tendency of such oils to oxidize. Oxidation results in rapid deterioration. Generally, heat oil to produce a viscosity of approximately 90 seconds Saybolt universal (90 SSU).

You should NEVER increase the pressure above normal to force a high-viscosity oil through the purifier. Instead, decrease the viscosity by heating the oil. Using excess pressure to force oil through the purifier results in less efficient purification. On the other hand, reducing the pressure at which the oil is forced into the purifier increases the length of time the oil is under the influence of centrifugal force and results in improved purification.

To make sure that the oil discharged from a purifier is free of water, dirt, and sludge, you need to use the proper size discharge ring (ring dam). The size of the discharge ring depends on the specific gravity of the oil being purified. All discharge rings have the same outside diameter; but, they have inside diameters of different sizes.

The information in this TRAMAN on purifiers is general, and it applies to both types of purifiers. Before you operate a specific purifier, refer to the specific operating procedures contained in the instructions that come with the unit.