Lantern rings are used in a pump stuffing box to:

• A. Prevent air from entering the stuffing box without causing excessive heat and wear on the shaft sleeve
• B. Increase pumping speed
• C. Cool the pump bearings
• D. Act as a fuse

Answer: (A)

Lantern rings are used to keep the stuffing box properly lubricated and to purge air from the packing area. The packing around a pump shaft needs lubrication to slide smoothly; if air enters the packing, lubrication cannot do its job, leading to heat buildup and faster wear on the shaft sleeve. The lantern ring sits in the packing assembly and has small passages that allow lubricant (or cooling fluid) to reach the packing and any air in the chamber to be displaced. This keeps the packing cool and well-lubricated, reducing heat and wear on the shaft sleeve and preserving the seal. It doesn’t directly change pumping speed, cool the bearings, or function as a fuse.