Centrifugal pump shaft seals

There have been tremendous advances in the design of centrifugal pump mechanical seals, yet many new pumps employ ancient rope-type packing to prevent product leakage around the shaft. 

NonmetalHc centrifugal pumps utilize polymers for all components coming into contact with the pumping media. Even the steel (qv) shaft is sleeved with plastic to isolate the shaft from the fluid. Mechanical seals are reversed so that the metal face does not come into contact with the corrosive... 

Labyrinth seals work best when the pump is running. Centrifugal force favors the labyrinth seal s action. Earlier models were only specified for horizontal pump shafts. Later models are designed for both horizontal and vertical pump shafts and effectively perform their function whether the pump is running or off... 

Shaft seal requirements and two common types of seals, packed stuffing boxes and simple mechanical seals, are described and discussed in this section. A packed box typically is used on slow- to moderate-speed machinery where a slight amount of leakage is permissible. A mechanical seal is used on centrifugal pumps or other type of fluid handling equipment where shaft sealing is critical. 

Standard 682 Shaft Sealing Systems for Centrifugal and Rotary Pumps... 

API Std 682 Shaft sealing systems for centrifugal and rotary pumps ... 

Sealing the Centrifugal Chemical Pump Although detailed treatment of shaft seals is presented in the subsection Sealing of... 

The shaft-seal development for high-pressure centrifugal pumps is quite similar to that explained for compressors. The traditional mechanical seals lubricated by liquids are now being partly replaced, for obvious reasons, by gas-lubricated ones. 

The main disadvantages of centrifugal pumps are the sealing of the impeller shaft and the inability of the pump to be self-priming. The latter is only a disadvantage if the pump cannot be positioned so that its suction is flooded (see Fig. 6.2). 

It is not always possible to use a standard stuffing box to seal the shaft of a centrifugal pump. The pump suction may be under a vacuum so that outward leakage is impossible, or the fluid may be too hot to provide adequate cooling of the packing. These conditions require a modification to the standard stuffing box. 

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