By Todd McMonigle

When repairing a pump that currently has a component mechanical seal* (or packing**), it is worth considering upgrading to a cartridge mechanical seal design. Component seals include multiple parts (rotor, rotor face, stationary face, springs, O-rings, gaskets, and seal gland) that require considerable handling and also require more care and skill during installation. For this reason you can incur potentially more assembly errors, including wrong spring setting—and therefore improperly loaded faces, dirt or grease contamination on sealing faces, damage to sealing components from mishandling, and sometimes just plain forgetting to use a needed part (like omitting a gland gasket…been there!). Any of these will result in immediate or early failure of the mechanical seal.  (Note: It is always a good idea to air test—at 25 psig—a rebuilt pump on the bench prior to putting it back into service).

On the other hand, a cartridge seal is a FULLY pre-assembled mechanical seal. It includes all of the parts mentioned above in the component seal (plus a seal sleeve), but in a prepackaged, preset, factory assembled and factory-TESTED product. All of the potential issues mentioned above with a component seal are eliminated with a cartridge seal. As with any mechanical seal installation, however, careful attention must be paid to proper installation practices and techniques—regardless of whether it’s a component or cartridge seal. Also, cartridge mechanical seals can sometimes require additional seal chamber clearance or axial space requirements; that is another reason to consider upgrading during a pump rebuild, when you have the tools and machining capabilities readily at hand (if needed).


  • Installation time is reduced considerably compared to a component seal installation
  • Seals come with installation grease, tools, a detailed drawing, and sometimes extra set screws and O-ring materials
  • Multiple features, seal designs, materials, single and double configurations, and internal interchangeability
  • Most manufacturers offer “half-price” repair programs or exchanges, often regardless of the poor condition of the seal
  • Manufacturers also provide further deep discounts on new seals when converting a competitor’s cartridge seal

For more information about component and cartridge mechanical seals, contact an OTP Industrial Solutions expert. Our team takes pride in the technical knowledge and broad product support we provide to help our customers build and maintain top performing industrial systems.

*Mechanical Seal – precision sealing device used to virtually eliminate process fluid leakage (as
low as 3 drops/day) along the pump shaft or other process equipment shaft.

**Packing – early method of sealing the pump shaft by means of compressing or squeezing
together multiple flexible rings or “ropes” to create a seal. Generally leakage rates are required to
be a minimum of 60 drops/minute and are often times much greater. Packing is still used today
quite extensively.