Two basic types of purifiers are used in Navy installations. Both types use centrifugal force. Principal differences in these two machines exist, however, in the design of the equipment and the operating speed of the rotating elements. In one type, the rotating element is a bowl-like container that encases a stack of discs. This is the disc-type DeLaval purifier, which has a bowl operating speed of about 7,200 rpm. In the other type, the rotating element is a hollow cylinder. This machine is the tubular-type Sharples purifier, which has an operating speed of 15,000 rpm.

Disc-Type Purifier

A sectional view of a disc-type centrifugal purifier is shown in figure 9-6. The bowl is mounted on the upper end of the vertical bowl spindle, which is driven by means of a worm wheel and friction clutch assembly. A radial thrust bear-ing at the lower end of the bowl spindle carries the weight of the bowl spindle and absorbs any thrust created by the driving action. The parts of a disc-type bowl are shown in figure 9-7.

Figure 9-7.-Components of a disc-type purifier bowl (DeLaval).

The flow of fuel through the bowl and additional parts is shown in figure 9-8. Con-taminated fuel enters the top of the revolving bowl through the regulating tube. The fuel then passes down the inside of the tubular shaft, out the bottom, and up into the stack of discs. As the dirty fuel flows up through the distribution holes in the discs, the high centrifugal force exerted by the revolving bowl causes the dirt, sludge, and water to move outward. The purified fuel is forced inward and upward, discharging from the neck of the top disc. The water forms a seal between the top disc and the bowl top. (The top disc is the dividing line between the water and the fuel.) The discs divide the space within the bowl into many separate narrow passages or spaces. The liquid confined within each passage is restricted so that it can flow only along that passage. This arrangement minimizes agitation of the liquid as it passes through the bowl. It also forms shallow settling distances between the discs.

Any water, along with some dirt and sludge, separated from the fuel, is discharged through the discharge ring at the top of the bowl. However, most of the dirt and sludge remains in the bowl and collects in a more or less uniform layer on the inside vertical surface of the bowl shell.