Evaluating centrifugal pump packing that has failed or reached the end of its useful life offers vital clues to help you make improvements in your next round of sealing. Failed packing can be a sign that the wrong packing is being used for the application or other possibilities ranging from excessive gland load to inadequate flush.
If your team takes the time to conduct a regular and detailed analysis of used/failed packing on your centrifugal pumps, you can identify the root cause of premature packing failure and take definitive steps.
Conduct methodical, continuous packing analysis to:
- Increase Mean Time Between Failures (MTBF)
- Extend the life of pump shafts
- Lower energy use and other costs
- Decrease maintenance efforts
So, let’s get started. Below is a quick checklist of what signs to look for and the possible root cause so you can identify the best solution.
Assess the Condition of the Packing Rings
As you remove the rings from the stuffing box, try to keep the rings in removal order to best determine the failure mode. Tag the removal order of each ring and bag up each packing sample, noting the date and MTBF. It could take several rounds of investigation to identify the true root cause of a packing issue.
Check rings for the following:
See if the solids are embedded in all the rings. This may indicate the following:
- Solids present in the flush
- If using clean flush, then a loss of flush pressure
- Loss of gland load or uneven gland load
Solids embedded in the packing lead to leak paths. The rings need to be in intimate contact to avoid the creation of leak paths.
If the packing appears to be burnt, the packing material being used may be inadequate to handle the shaft speed limit.
Soft or Mushy Packing Rings
Soft or mushy packing could indicate a chemical attack from the sealed media or by the cleaning fluid used on the pump. The selection of packing with the appropriate pH would be recommended.
Brittle or Weakening Packing
This can indicate incompatibility with the process medium.
Signs of Packing Extrusion
Packing extrusion is typically caused by improper clearances between the box, gland, shaft, and lantern ring.
- For top ring ID extrusion, check for excessive clearance in gland ID
- A top ring OD extrusion is indicative of a worn gland
- For bottom ring ID extrusion, check for excessive shaft run-out, bad bearings or worn box throat
- For extrusion around the lantern ring, check that the lantern ring is properly sized
Assess the Condition of the Packing Fibers
You’ll want to examine:
Torn/Badly Worn, or Fractured Fibers
Check the ID and OD for fiber wear. This could indicate the wrong fiber is been used or the shaft/sleeve surface is damaged.
This could indicate a cocked gland. To determine if the packing is unevenly compressed, measure the cross-section in four locations of the ring 90 degrees apart and compare the measurements.
Cutting of the Rings
Was the cut skive or butt? Does it appear to be a sharp cut and do the ends match up? We recommend always purchasing pre-cut and pre-formed rings. Always follow the packing manufacturer’s cutting instructions and best practices to ensure the optimal fit for performance.
Most Common Failure Points
The four most common reasons that pump packing fails are:
- Poor Solids Removal
- Incorrect Packing for the Specific Application
- Pump Condition
- Poor Installation
For a more detailed understanding of failure analysis of centrifugal pump packing and how to solve it, contact your local distributor.