There are three main reasons why compression packing fails in the stuffing box:
Excessive shaft speeds;
Improper selection of the compression packing;
Improper installation of the packing.
Addressing these issues can dramatically improve the performance of your compression packing.
Media attack, or chemical wear, used to be a prevalent reason for compression packing failure, but is less so now with the advent of newer packings. Most types of packing available on the market will service pH ranges from 0-14, which will address most media servicing issues. Nonetheless, there are still some cheaper packings available on the market which only service a pH range of 2-12. While these packings are cheaper, they will not perform as well under severe service conditions.
Addressing the issue of excessive shaft speeds, carbon and graphite packing is designed and manufactured to service a maximum shaft speed of 4,500fpm. With pump manufacturers designing some pumps to operate at 3,600 RPM, these two different measures of operating parameters can spell failure in some circumstances, particularly with condensate pumps. If these types of pumps run for even a short time without cooling water at these speeds, the lubricant in the packing will burn out, hardening and glazing the packing and making it no longer usable.
At these operating speeds, there is a good chance of catastrophic failure of the pump, should the pump run dry for any length of time. This can occur no matter what type of packing is used, even if the packing has extra lubricant or special blocking agents incorporated into it. Therefore, special care should be taken with pumps at elevated shaft speeds of 3,000 RPM or higher.
If you have a slow reciprocating pump, and the packing is still a problem in the stuffing box and not working to expectations, the cause is likely to be an improper installation of the packing. Achieving a good installation of compression packing into stuffing boxes is becoming a lost art. There are 10 important steps to follow when installing compression packing, and omitting any one step can result in a failed installation. Refer to our April blog Tips for Installing Compression Packing for guidance on how to successfully install packing into the stuffing box.
When you do experience a packing failure, consider this as a learning opportunity. Never discard the failed packing without first examining and inspecting it closely. At the same time, inspect the stuffing box carefully. A good thorough inspection of the packing and stuffing box can often provide clues as to what the cause of failure is.
For example, if the bottom of the stuffing box is badly worn, with packing extruded into the whole system, then a whole ring or part ring is missing from the packing set. Another common cause of failure is that the rings are loose or rotating with the shaft in the stuffing box. Similarly, if inspection reveals that there is excessive wear on one or more of the rings, then the packing selected was most likely too small.
Finally, the most common reason for packing failure is exposure of the packing to excessively high temperature and lack of lubrication. The most telling clue in this case is that the wearing surface of the packing rings would be charred and dried, with the rest of the packing in good condition.
At Canada Rubber Group Inc. (CRGI), we carry a full line of quality compression packing from Teadit North America.
To find out how CRGI can help with your compression packing needs, contact our sales department at crg@canadarubbergroup.com.