Centrifugal pump mechanical seal/packing

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. 

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. 

Mechanical seals have fully established themselves for all types of centrifugal pumps in a variety of services. Though more costly than packing, the mechanical seal reduces pump maintenance costs. 

Centrifugal and positive displacement stainless steel pumps are most likely used in plasticizer transfer. The pumps should have mechanical seals instead of packing glands as required by environmental regulations. Check valves should be used on pump discharges to avoid contamination by back flows. Pumps and pipes should be made from the same material as used for tank construction to avoid galvanic corrosion... 

Packed pump Centrifugal pumps that handle water or nonhazardous liquids do not use a mechanical seal. They use a cheaper and simpler packed seal. 

The 1889 text does not mention mechanical seals, as they did not exist then. These early centrifugal pumps were packed pumps. My old shift foreman, Henry Ziprean, showed me how to replace the packing for a sour water pump during the long strike in 1974 in Texas City. 1 have only done this twice, 39 years ago. But, since I did it with my own hands, I ve never forgotten the details. 

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