Benefits of Graduating from Packing to Mechanical Seals | John Crane

Benefits of Graduating from Packing to Mechanical Seals

April 3, 2019 | 2 minute read

The environmental performance of products and processes in all industrial sectors is increasingly coming under critical inspection—with sustainability, conservation of natural resources and reduced environmental contamination directly influencing the design and selection of equipment. Many industrial processes can improve sustainability, water use and energy efficiency, as well as minimize environmental impact while maintaining or reducing operating costs.

Included in these processes is mission-critical rotating equipment, specifically centrifugal pumps, which represent a significant proportion of the equipment in most industrial manufacturing and processing operations.

Sealing systems are vital in maintaining pump efficiency, reliability, energy consumption, water usage and control of emissions to the environment. An alternate to traditional compression packing is the mechanical seal, which resolves many of the sustainability and environmental-impact issues inherent in compression packing. These mechanical seals require a much lower water and energy demand, and have substantially reduced leakage, making them much more efficient at containing volatile or hazardous fluids, aqueous solutions and slurry suspensions. In addition, mechanical seals require no maintenance, once installed.

A mechanical seal is comprised of a stationary primary element which is fixed within the pump housing, and a rotating mating element fixed to the shaft. Precisely machined, these two components are pressed together by a flexible load element, meeting at a wear face, while the extreme tolerance precisions between the two elements minimize leakage. The wear faces are supported on an extremely thin lubricating film, typically 0.25 microns (9.8 microinches) in thickness.

Available in a wide variety of types, arrangements and materials, mechanical seals are found in the majority of centrifugal pumps today.

Minimized Water Consumption and Leakage

Mechanical seals require very little flush water needed to be injected into the seal chamber when compared to compression packing installed in the same service.

Abrasive pumping applications pose a significant challenge to compression packing as significant volumes of water is required to be injected into the stuffing box to prevent damage to the packing rings and shaft sleeve by the abrasive particles. A mechanical seal designed for abrasive services only a small fraction of this water volume to operate reliably.

Reduced Power Consumption

The amount of power required to drive a mechanical seal is up to 80 percent less when compared to compression packing, primarily because the seal faces have less frictional energy losses due to the extremely precise mating between the stationary and rotating elements. Additional energy reduction requirements take the form of the reduced need for flush water to be pumped into the seal, which is required with compression packing.

Maximum Sealing Safety

Designed to ensure maximum sealing safety, dual mechanical seals are typically defined as a single assembly that contains a pair of seals. A cavity is formed between the two seals within the assembly that is filled with a barrier or buffer fluid that separates the pumped liquid from the atmosphere and environment.

Dual mechanical seals allow for near complete control over the seal operating environment and the fluid film lubricating the seal faces. They provide maximum elimination of leakage to atmosphere of the fluid being handled in centrifugal pumps.

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