Component or Cartridge

How to Choose the Right Seal
Mechanical seals are used in pumps to prevent fluid leakage between a rotating shaft and stationary housing.  They consist of a rotating element and a stationary element, each with a lapped, precision-smooth mating face.  Seal performance is determined primarily by the condition of the faces and the pressure applied to them.  Other key factors include heat, vibration and the fluid characteristics.  Depending on the application and user's requirements, different seal types may be appropriate.

Component Seals

The majority of smaller pumps today use component seals as they are inexpensive and work well for many pumping applications.  Component seals are typically installed piece-by-piece and require special handling and careful installation.  The spring tension can be manually set by the pump technician and if it is set improperly, the seal may leak and the pump may require disassembly.

Cartridge Seals

Larger pump designs, such as ANSI process, vertical turbine & split case pumps offer the flexibility of utilizing a cartridge seal.  While cartridge seals are typically more expensive compared to component seals, there may be long-term benefits that can justify the increase in price.  Cartridge mechanical seals and component seals use similar components, but the stationary components are preassembled in a housing, and the rotating components are preassembled on a shaft-mounted sleeve that is sealed with an o-ring.  With cartridge seals, the spring tension is preset.  To ensure the proper tension, a retaining device holds the rotating and stationary elements in alignment until after the seal is mounted.

Component vs. Cartridge

Cartridge mechanical seals may cost two to three times compared to component seals.  Despite the higher initial investment, a cartridge seal can be a more cost-effective, long term solution.  Below are the advantages of using a cartridge seal over a component seal.
  • Ease of Installation - Cartridge seals are easier install since all components are preassembled.  If a technician doesn't set proper spring tension in a component seal, the pump can leak and the seam may be permanently damaged.  Cartridge seals include a retaining device that holds the rotating and stationary elements in alignment until after the seal is mounted.  While a competent pump technician might not find this to be a great benefit during a planned pump overhaul, it can be extremely beneficial during an emergency outage.

  • Split Seal Designs - Cartridge seals can be found in a split-design allowing the replacement of the seal to be performed with minimum disassembly of the pump and/or motor.  This can greatly reduce downtime during an emergency outage.  Split seals are an excellent consideration for split case and some larger vertical turbine pumps.

  • Impeller Adjustment - Some pumps, particularly those with semi-open impellers, require periodic adjustment of the impeller face clearance.  Users can make this adjustment by moving the pump shaft axially, which can change the tension on the seal.  On a components seal, resetting the seal tension requires significant disassembly of the pump.  Most cartridge mechanical seals have retaining devices that can be reinstalled to align the stationary and rotating elements.  This makes it easy to reset the seal tension after the impeller face clearance has been adjusted.

Making the Right Choice

If users are aiming to find the most cost-effective, long-term solution to pump maintenance and they anticipate in-service seal replacement, a cartridge mechanical seal will likely be a good choice.  Incorporating a cartridge mechanical seal also allows the conversion from a packing seal to a mechanical seal.  When low initial cost is important, component seals and a well-trained pump technician are the best option.