Packing Failure and Replacement

Packings are a very simple and cost-effective way to seal a pump. Incorrect selection of material type, poor installation practices and misaligned or bent shafts can all cause premature seal failure. However, there are two additional problems that are at the root of the majority of packing failures.

1) Solids contamination is a primary source of failure for many packed boxes. Whether it’s from clear process liquids that mistakenly contain some solids, contaminated seal flush water or the simple loss of pressure in a properly designed slurry flush system, the result is the same. Solids enter the packing box, become embedded in the soft packing material and form a very effective grinder that quickly destroys the shaft sealing surface as it rotates.

As the illustration to the right shows, constant adjustment of the packing can fill the gap formed as the shaft is ground away, but premature failure is unavoidable.

2) Glazed or burnt (carbonized) packing material will not form an effective seal. Packing glands rely on process fluid or external flush/quench fluids for cooling. If for any reason the flow across the packing material is interrupted, the surface of the packing material quickly overheats and becomes glazed or carbonized. The glazed surface seals in the impregnated lubricants that are an integral part of the packing. Without this critical source of lubrication, sealing fail and repairs are required.

Pumps that have no flush/quench system installed can lose the flow across the packing gland due to dry running of the wet end or to a compression gland that is simply over tightened. Note: Pumps with properly engineered flush/quench systems also  lose cooling and fail due to faulty regulators or operators inadvertently shutting off the cooling water.

Packing Replacement 

Assuming that the reason or reasons for seal failure have been rectified it is now time to replace the damaged seals.  The 9 steps listed below will guide you through installation and adjustment of common packing.

1) Remove all of the used pump packing rings and the lantern ring. Thoroughly clean and inspect the stuffing box. Replace worn shaft sleeve if needed.

2) Cut the required amount of packing rings, making sure to use a mandrel equal to the shaft size and  cut at 45 degrees.

3) Coat each new packing ring with an appropriate lubricant.  Liquid soap is often recommended for common packing rings.  Never use Anti-Seize or any metallic based compound on the pump packing!

4) Install each packing ring individually, indexing joints 90 degrees and carefully seating each packing ring in the bottom of the stuffing box. Use a split bushing or a tamping tool. NEVER use a screwdriver or a sharp tool.

(If a flush is used don’t forget the lantern ring and position it to line up with the flush port. )

5) Check to make sure the lantern ring is properly located. This is done by inserting a small object through the flush port and feeling the lantern ring.

6) After the proper amount of rings have been installed, install the gland follower and run the gland nuts up finger tight only.

7) Install any flush set-up required, and start flushing the stuffing box. It is also important to start the flush before allowing fluid to enter the inlet to the pump.

8) Start the pump and allow the packing to leak freely at start-up. During the break-in period, adjustments should be made gradually (one flat at a time), allowing 5 to 10 minutes between adjustments

9) After the break-in period, a typical leakage rate is to 10 to 12 drops per minute per inch of shaft sleeve diameter. (All leakage being from the ID of the packing.)

As always should you need any advise or help with a Toyo seal box please feel free to contact our very competent engineering team.

Cheers

RJ