Shafts, rotating, sealing equipment

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. 

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. 

It is important to maintain correct levels in the hoppers into which the elevators discharge. Too high a level causes spillage of catalyst, and too low a level results in insufficient pressure in the reactor seal leg. Hoppers in some units are equipped with a continuously rotating vertical shaft with paddles which ride on the surface of the catalyst the position of the upper end of the shaft is communicated to the control room by means of a pneumatic transmitter (185,191). 

If equipment is not used for a few weeks or months, and is then restarted, it may be found that it may not work as it should. For example, pump shafts may have bent out of alignment, pockets of corrosive materials may have formed at the base of storage tanks, instruments contacts may have covertly failed, equipment and piping may have corroded, rotating equipment shafts may have bent, and seals may be degraded. 

Packing is used to seal shafts in a variety of applications. In equipment where the shaft is not continuously rotating (e.g., valves), packed boxes can be used successfully without any leakage around the shaft. In rotating applications, such as pump shafts, the application must be able to tolerate... 

Seal failures are the most common type of failure associated with rotating equipment. Since seals are a barrier between the process and the atmosphere, such failures are often likely to lead to environmental problems, and potentially a safety problem depending on factors such as the flammabUity/toxicity of the process fluid, the size of the leak, and its proximity to personnel or ignition sources. Seal failures can be caused by problems with the bearings, couplings, and shaft vibration. 

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