A Cartridge Seal is a self-contained, pre-assembled mechanical seal unit where all the components (faces, bellows/springs, shaft sleeve, and gland plate) are built into a single housing at the factory.
Unlike a “component seal,” which requires a technician to manually measure and install each part onto a pump shaft, a cartridge seal is slid onto the shaft as a complete package.
Why “Cartridge” is the Industry Standard
The primary reason for using cartridge seals is to eliminate installation error, which is the leading cause of premature seal failure.
- Pre-Set Tension: The internal springs are compressed to the correct working length at the factory. You don’t have to measure “seal height” or “axial compression” yourself.
- Self-Alignment: Because the components are held together by a gland and a sleeve, the seal faces are perfectly aligned before they even touch your equipment.
- Ease of Replacement: Since the unit is “plug-and-play,” it can be swapped out much faster during a breakdown than a component seal.
How it Works (The Installation Tabs)
The defining feature of a cartridge seal is the centering tabs (or spacers). These small metal clips hold the rotating and stationary parts in the exact correct position during shipping and installation.
- You slide the seal onto the shaft and bolt the gland to the pump housing.
- You tighten the set screws to lock the seal’s internal sleeve to the shaft.
- Crucial Step: You remove or rotate the centering tabs. This “frees” the seal to spin with the shaft while the gland remains stationary.
Component vs. Cartridge: A Comparison
| Feature | Component Seal | Cartridge Seal |
| Installation | Difficult; requires precise measurements. | Easy; “Slide on and bolt down.” |
| Reliability | High risk of human error (dirt, wrong tension). | Low risk; pre-assembled in clean labs. |
| Cost | Lower initial purchase price. | Higher initial price, lower labor cost. |
| Repair | Can replace individual faces. | Usually replaced as a whole unit. |