Gland packing
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Frequently asked questions
How do I size gland packing?
Packing size equals (stuffing box bore minus shaft diameter) divided by two. For a 60 mm box and a 40 mm shaft, use 10 mm square section. Packing that is too large has to be forced in and heats the shaft; too small will not seal.
How do I choose packing material for the medium?
PTFE packing suits chemicals and food duty; graphite handles high temperature and steam and conducts heat well for fast shafts; aramid fibre is hard and resists abrasion in slurries and dirty water, but can wear a shaft that is not hard enough. Ordinary grease-impregnated fibre packing is for clean water at low temperature.
How should packing rings be fitted in the stuffing box?
Cut each ring separately around a mandrel of shaft size, with a 45 degree skive cut. Fit one ring at a time, seat it fully and stagger the joints by about 90 to 120 degrees from ring to ring. Never wind in a continuous spiral.
Should a packed pump be allowed to drip?
Yes. On a rotating shaft, a controlled drip is needed to lubricate and cool the contact face. Tightening until completely dry burns the packing and grooves the shaft; adjust the gland nuts evenly in small steps with the pump running.
When must all packing be replaced rather than adding one ring?
When the gland follower has run out of travel, leakage rises right after adjustment, or the packing is burnt hard, remove every old ring. Adding one ring on top of hardened old rings will not seal for long and also wears the shaft. Use proper packing extractor hooks so the shaft and stuffing box are not scratched.
How should new packing be run in?
Tighten the gland only finger tight, start the pump and allow fairly heavy leakage for the first few minutes. Then tighten in small steps of about one sixth of a nut turn, letting the temperature settle before each further step. The goal is a small steady leak with the stuffing box only warm, not hot to touch.
What should I do when the shaft is grooved under the packing?
A groove stops new packing from conforming, so it leaks straight after replacement. Measure the groove depth: shallow marks can be polished out, while deep wear calls for a new shaft sleeve or hard facing of the packed area. Usual causes are overtightening, packing unsuited to the medium, or a blocked flush line to the stuffing box.
What is a lantern ring in a stuffing box for?
A lantern ring is a hollow ring placed between packing rings, lined up with the flush or sealing liquid port. It distributes clean liquid around the shaft to cool and lubricate it and to keep solids in the pumped medium out of the packing. When repacking, the lantern ring must go back in its original position, since a ring offset from the port does nothing.
