Shafts, rotating, sealing lubricant

Equipment seals on rotating shafts such as agitators, pumps, and compressors should avoid contact with products. Otherwise, seal lubricants should be food grade where permitted by the manufacturer. 

Then, the oil film breakdown ratio increases from the minimum value of 2% to 10% with fluctuation. This tendency is probably caused by a temperature of 5 C in the body of the seal lip slightly higher than the temperature of the surface where the temperature of the lubricating oil is controlled to 3012 C. In this region, although the oil film is formed by the speed effect, the viscosity decreases, and the followability of the seal lip to shaft rotation is increased due to heat generation in the seal lip. When these two factors occur simultaneously, the micro asperities on the surfaces of the shaft and the seal lip do not easily contact with each other and also the oil film is broken. Thereby, the waveform ( ) of lip motion is obviously different up to this point in the elliptical motion... 

Face lubricated-type seals must be connected from the source of lubrication to the tap openings in the seal gland before startup. This is another predetermined environmental control feature that is mandatory for proper seal function. Where double seals are to be operated, it is necessary that the lubrication feed lines be connected to the proper ports for both circulatory or dead-end systems before equipment startup. This is very important because all types of double seals depend on the controlled pressure and flow of the sealing fluid to function properly. Even before the shaft is rotated, the sealing liquid pressure must exceed the product pressure opposing the seal. Be sure a vapor trap does not prevent the lubricant from reaching the seal face promptly. 

The seal is formed between two flat faces, set perpendicular to the shaft. One face rotates with the shaft, the other is stationary. The seal is made, and the faces lubricated by a very thin film of liquid, about 0.0001/i.m thick. A particular advantage of this type of seal is that it can provide a very effective seal without causing any wear on the shaft. The wear is transferred to the special seal faces. Some leakage will occur but it is small, normally only a few drops per hour. 

Figure 7.13. Types of seals for pump shafts, (a) Packed stuffing box the sealing liquid may be from the pump discharge or from an independent source, (b) Water cooled stuffing box. (c) Internal assembly mechanical seal the rotating and fixed surfaces are held together by the pressure of the pump liquid which also serves as lubricant a slight leakage occurs, (d) Double mechanical seal with independent sealing liquid for handling toxic or inflammable liquids.

Mechanical seals prevent leakage at the rotating shaft by sliding metal on metal lubricated by a slight flow of pump liquid or an independent liquid [Figs. 7.4(c) and (d)]. 

The system operating pressure is contained by a double-row cooled and lubricated carbon mechanical seal between the casing and rotating shaft in the vapor space at the upper end of the centrifuge assembly. 

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