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Sharples Purifier

Lubricating oil clarifier

a. General. Clarification of the lubricating oil is accomplished by the Sharples centrifuge which also serves as the fuel oil purifier (Section 5C4). The machine is set up as a clarifier by installing a clarifier sleeve, or ring dam, on the top of the bowl, thus closing the outlet passage through which the water is discharged. The term clarifier is applied to the machine when it is set up to discharge a single liquid from which solid matter has been removed by centrifugal force. If the machine is set up to separate two liquids from solid matter and from each other (such as oil and water in a fuel oil purifier) it is called a separator. The machine is usually set up as a separator for fuel oil purification and as a clarifier for lubricating oil purification.

The lubricating oil purifier consists essentially of a rotor, or bowl, which rotates at high speeds. It has an opening in the bottom to allow the dirty lubricating oil to enter and two sets of openings to allow the oil and water or the water by itself to discharge. The bowl, or hollow rotor, of the centrifuge is connected by a coupling unit to a spindle which is suspended from a ball bearing assembly. The pulley of this bearing assembly is driven by an endless belt from an electric motor mounted on the rear of the frame. Tension on the belt is maintained by an idler pulley.

The lower end of the bowl is entered into a drag bushing mounted in the drag assembly. This is a flexibly mounted guide bushing. Inside the bowl is a three-wing partition consisting of three flat plates equally spaced radially. The three-wing partition rotates with the bowl and its purpose is to force the liquid in the bowl to rotate at the same speed as the bowl. The liquid to be centrifuged is fed into the bottom of the bowl through the feed nozzle under pressure so that it jets into the bowl in a stream. For lubricating oil clarification the three-wing partition has a cone on, the bottom against which the feed jet strikes to bring the liquid up to speed smoothly without making an emulsion. This cone is not necessary for fuel oil separation since fuel does not have the tendency to emulsify.


b. Operation. When a mixture of oil, water, and dirt stands undisturbed, gravity tends to effect a separation into an upper layer of oil, an intermediate layer of water, and a lower layer of the solid. When the mixture is placed in a rapidly revolving centrifugal bowl, the effect of gravity is negligible in comparison with that of centrifugal force, which acts at a right angle to the vertical axis of rotation of the bowl. The mixture tends to separate into a layer of solids against the periphery of the bowl, an intermediate layer of water, and a layer of oil on the inner surface of the water. The discharge holes of the bowl may be so arranged that water can be drawn off and discharged into the upper cover. The solids will deposit against the wall of the bowl, to be cleaned out when necessary or as operations permit.

If an oil contains no moisture, it need only be clarified, since the solids will deposit in the bowl, and the oil will discharge in a purified state. If, however, the oil contains some moisture, the continued feeding of wet oil to the bowl results eventually in a bowl filled with water, and from that time on, the centrifuge is not accomplishing any separation of the water from the oil. Even before the bowl is completely filled with water, the presence of a layer of water in the bowl reduces the depth of the oil layer. As a result, the incoming oil passes through the bowl at a very high velocity. This higher velocity means that the liquid is under centrifugal force for a shorter time, and the separation of water from the oil is, therefore, not so complete as it would be if the bowl were without the water layer, or if the water layer were a shallow one. Because of this, the centrifuge should not be operated as a clarifier unless the oil contains very little or no water. A small amount of water can be satisfactorily accumulated, together with the solids, to be drained out when the bowl is stopped for cleaning, but if there is any appreciable amount of water in the oil, the bowl should be operated as a separator.

The length of time required to clarify lubricating oil is determined to a great extent by the viscosity of the oil. The more viscous the oil, the longer it takes to purify it to a given degree of purity. The use of a pressure in excess of that normally used to force a high-viscosity oil through the purifier will result merely in less efficient purification. Decreasing the viscosity of the oil by heating is therefore one of the most effective methods of facilitating purification.

The capacity rating of the centrifuge is based on the use of 2190 oil at 130degree F, which represents a viscosity of approximately 200 SSU. For good results no oil should be purified at a higher viscosity than this and other oils may need to be heated above 130degree' F to reach 200 SSU. (See temperature table below.)

A reduction in the pressure at which the oil is forced into the centrifuge will increase the length of time the oil is under the influence of centrifugal force, and therefore will tend to improve results. The effective output of the machine in any case will depend on viscosity, pressure, the size of the solid particles, the difference in specific gravity between the oil and the water, and the tendency of the oil to emulsify. If a used lubricating oil contains no water, but merely metallic particles, it may be cleaned at a higher rate (high input pressure). If the same oil contains a large percentage of water, and has a tendency to emulsify, the input pressure will necessarily have to be lower to obtain the required degree of purity.

Oil, Navy SymbolTemperature*
in degrees F
Oil, Navy SymbolTemperature*
in degrees F
Oil, Navy SymbolTemperature*
in degrees F
104289 2135116 5065 143
1047102 2190 129 5150 190
1065137 2250 142 5190 209
1080151 3050 119 6135 192
1100166 3065 135 7105 173
1120179 3080 154 8190 128
1150190 3100 163 9170 123
207592 3120 180 9250 140
210095 4065 140 9370 158