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The Important Role of Shaft Seals on Your ANSI Centrifugal Pump

by PSG

A leaking centrifugal pump can create costly, time-consuming repairs and potentially hazardous working conditions, making proper sealing technique crucial in pump set-up and maintenance. No matter the type or the application, your pump’s shaft seals should be inspected and replaced regularly as part of essential centrifugal pump maintenance.

ANSI centrifugal pumps function by channeling fluid through the pump’s suction, energizing the fluid using an impeller, then forcing the fluid to exit through the pump discharge. Since the impeller is supported and powered by a shaft that goes to the back of the pump, it creates a potential leak path. To prevent a leak, users must install a shaft seal.

Shaft seals can take on different forms within ANSI centrifugal pumps. One of the earliest forms of shaft seals involved rope, or what is now known as packing. The packing was wrapped around the shaft and pressed into the seal chamber using a packing gland. As the gland tightens, it compresses, holding the packing in place and filling any dead space to minimize leaks. To function properly, packing seals need regular lubrication.


While packing seals have been used for many years because of their simplicity and low cost, their simple design and features may not hold up over time, prompting regular replacement as the packing material degrades and leaks occur. For these reasons, packing seals are unsuitable for hazardous fluid applications.

The next type of seal we’ll discuss is the mechanical seal. Comprised of various components fitted together and installed into the pump, these seals were created to eliminate or reduce leaks by incorporating many sealing points into their design. In addition, mechanical seals were used to eliminate “wet seals'' that require constant moisture and lubrication. Over the years, mechanical seals have proven to be a more durable option than packing seals. However, early mechanical seals were challenging to install and required a precise fit, leading to long installation times. While mechanical seals have become simpler over time, they still require installers to decouple the drive shaft, a considerably lengthy process.

Cartridge seals were created to help improve and simplify the installation of mechanical seals. Cartridge seals are self-contained sealing systems with preassembled components, giving them superior installation time when compared to other seal types. Cartridge seals also eliminate the precision required to use mechanical seals because they come with machine-accurate axial settings, reducing user error during the installation process.

To learn more about centrifugal pumps, pump seals, and installing cartridge and component seals on a Griswold® 811 ANSI Series Pump, click here for videos and related posts.