One common mistake is the tendency to maximize the packing's time in service to a perceived point of failure before replacing it. Defining failure is more a matter of opinion than science.

Signs that the packing has failed include increased leakage, smoke at the stuffing box or uncontrolled leakage at the gland.

Safety-conscious operators service the pump and replace the packing at regular intervals. However no common criteria for determining the replacement frequency or relating it to the packing material are available. An acceptable replacement cycle time is heavily dependent on the application, the equipment and the packing.

The confusion occurs because of the forgiving nature of compression packing. Pump operation is not impaired until the packing fails. It should be replaced long before this occurs. For any type of packing, operating costs are relatively fixed when it is functioning correctly. As performance deteriorates, operating cost increases are much larger than the initial cost of the packing ring set.

Based on the way packing works, three factors affect costs:

Power loss, shaft/sleeve abrasion and material wear caused by friction

External flush fluid leak rate from the stuffing box to dissipate heat caused by friction

Labor to adjust gland pressure to maintain minimal leak rate from the stuffing box

The best practice is to monitor changes at the stuffing box and replace the packing before costs increase. There are many costs, and depending on each application any of these costs could be the most significant. For example, the cost of product loss and product dilution could be much higher than power consumption or flush water losses depending on location and the cost of labor.

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