Stem Galling Caused by Cocked Packing Gland

Problem

Cocked packing gland can easily cause damage to the valve stem. Once stem damage has occurred, damage to the packing will follow and eventual packing leaks or failure. Several techniques are available to prevent or minimize this potential for stem damage.

Solution

Several simple techniques have been identified to prevent or minimize cocking of packing glands:

• Increase packing gland insertion. The further the packing gland can be inserted into the stuffing box the better the gland is supported and prevented from cocking. Typical practice is to minimize gland insertion to 1/8” to ¼” to allow for more packing takeup when the valve packing leaks. With today’s modern valve packing, “leak-free” service can be obtained and with the need for very little takeup in the future. Today’s recommendation for gland insertion depending the dimensions are:
  • Insert at least ½ of the gland
  • Allow for ~ 1 to 1 1/2 packing rings of take-up
• When consolidating valve packing or retorquing packing, insure the gland alignment is maintained straight (see drawing), this alignment check can easily be performed with the use of thin shim stock. While tightening the packing continually check for packing gland mis-alignment with shim stock.
• Live loading of valve packing can introduce packing gland cocking as the packing experiences in-service consolidation.
  • Only use Live-loading of valve packing for cause
  • Insure when valve packing is installed it is fully consolidated, and DO NOT rely on the live-loading to consolidate the packing