Two basic types of purifiers are used in Navy installations, and both types use centrifugal force. There are principal differences in the equipment design and operating speed of the rotating elements of the two machines. 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

Figure 10-33 shows a cutaway view of a disc-type centrifugal purifier. The bowl is mounted on the upper end of the vertical bowl spindle, and driven by a worm wheel and friction clutch assembly. A radial thrust bearing at the lower end of the bowl spindle carries the weight of the bowl spindle and absorbs any thrust created by the driving action. Figure 10-34 shows the parts of a disc-type bowl. The flow of fluid through the bowl and additional parts are shown ir figure 10-35. Contaminated fluid enters the top of the revolving bowl through the regulating tube. The fluid then passes down the inside of the tubular shaft, out the bottom, and up into the stack of discs. As the dirty fluid 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 fluid 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 fluid.) The discs divide the space within the bowl into many separate narrow passages or spaces. The liquid confined within each pass is restricted so that it flows only along that pass. This arrangement minimizes agitation of the liquid passing through the bowl. It also forms shallow settling distances between the discs.

Any water separated from the fluid, along with some dirt and sludge, 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.

Tubular-Type Purifier

A cutaway view of a tubular-type centrifugal purifier is shown in figure 10-36.  This type of purifier consists of a bowl or hollow rotor that rotates at high speeds. The bowl has an opening in the bottom to allow the dirty fluid to enter. It also has two sets of openings

Figure 10-34.-Parts of a disc-type purifier bowl.

Figure 10-35.-Path of contaminated oil through a disc-type purifier bowl (Delaval).

at the top to allow the fluid and water to discharge. The bowl of the purifier is connected by a coupling unit to a spindle. The spindle is suspended from a ball bearing assembly. The bowl is belt-driven by an electric motor mounted on the frame of the purifier.

The lower end of the bowl extends into a flexibly mounted guide bushing. The assembly restrains movement of the bottom of the bowl, but it also allows the bowl enough movement to center itself during operation. Inside the bowl is a device with three flat plates that are equally spaced radially. This device is commonly referred to as the THREE-WING DEVICE, or just the three-wing. The three-wing rotates with the bowl and forces the liquid in the bowl to rotate at the same speed as the bowl. The liquid to be centrifuged is fed, under pressure, into the bottom of the bowl through the feed nozzle.

After priming the bowl with water, separation is basically the same as it is in the disc-type purifier. Centrifugal force causes clean fluid to assume the innermost position (lowest specific gravity), and the higher density water and dirt are forced outward towards the sides of the bowl. Fluid and water are discharged from separate openings at the top of the bowl. The location of the fluid-water interface within the bowl is determined by the size of a metal ring called a RING DAM or by the setting of a discharge screw. The ring dam or discharge screw is also located at the top of the bowl. Any solid contamination separated from the liquid remains inside the bowl all around the inner surface.