Top 3 Reasons Why Packing Fails

(Above) Reason 2: Improper installation of packing seal can lead to damage of a shaft due to shaft-sleeve area being impossible to seal.

            When sealing pumps, there are two major types of seals most frequently used: mechanical seals and packing seals (AKA compression packing). Most of the seals on pumps are mechanical seals, though packing seals are sometimes used instead. Packing is usually chosen over mechanical seals because packing seals are much less expensive, as well as being easier to install— for the shaft does not need to be decoupled when packing is chosen. Still, pump packing will fail at some point in time. Ideally, pump packing should be installed properly in order to prevent failures. The following are the top three reasons why pump packing fails:

            Pump packing is located in a pump’s stuffing box. One of the reasons for packing failures occurring prematurely is due to foreign solids embedded underneath the packing, specifically located in the inner diameter of the packing ring1. Because of these contaminants, the packing may not be able to properly seal the shaft and will typically lead to excessive leakage, usually in copious and uncontrollable amounts. For packing seals usually leak at a constant rate, though not excessively. The best means of preventing solids underneath the packing would be to properly ensure that the both the shaft and coupling are clean and spotless, as well as keeping packing in safe areas (such as in a sealable plastic bag) beforehand.

            Next, the second reason why a pump’s packing may fail can be due to improper application of a packing seal. That is, when a packing seal is used when a mechanical seal should be used instead. For example, continuing from the previous paragraph on contamination: the next best method of preventing packing failures due to contamination would be to evaluate whether or not packing is appropriate for the type of pump being troubleshot: for example, a self-priming “trash pump” with an open impeller designed to pump both liquids and solids/semisolids would not be appropriate for a packing seal. Rather, a mechanical seal should be used instead of packing due to the ability of a self-priming pump allowing it to continuously pump foreign objects and liquids with ease.

            The third and final reason why packing tends to fail is due to improper installation. Therefore, in order to determine the cause for packing failure: “Look for clues in the old packing. If the packing you’ve removed is thinner in one area of the inside surface, then the shaft is improperly aligned. If there is raggedness or shredding on the inside surface, you’ll probably also find chipping or burrs on the shaft sleeve. When the old packing has become hard or abrasive, …either the wrong packing material was used, or the stuffing box is worn, (pores are damaged or clogged), causing the gland water to flow outside the packing rings and not cool them properly.”2 Despite improper installation seeming an obvious and thus overlooked cause for packing failure, it is often one of the most common causes of seal failure on the sleeve, and can also lead to catastrophic failure of a pump— as well as the very high cost for replacing a drive shaft.

            Though packing seals are much less expensive and easier to install than a mechanical seal, they are not indestructible nor infallible: for every part has its pros and cons, as well as its best application. Hence, the best means of utilizing packing seals in pumps would be to apply packing seals appropriately as advised.


  1. https://blog.chesterton.com/sealing/pump-sealing-options-packing-vs-mechanical-seals/
  2. https://www.manufacturing.net/home/article/13217602/how-to-avoid-pump-packing-failures