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Wednesday, July 15, 2009

Gland Packing

For packing to operate properly, the finish on the shaft sleeve must be at least 16 µin (o.4 µm) centerline average (CLA) and the finish in the bore should be 63 µin (1.65 µm) CLA. The sleeve must be harder than the packing and chemically resistant to the liquid being sealed. If the sleeve has a coated material for a hard wear surface, the sleeve must also have good thermal shock resistance.

Lantern Ring (Seal Cages)When an application requires that a lubricant be introduced to the packing, a lantern ring is used to distribute to flow. This ring is used or near the center of the packing installation. For ease of assembly, most lantern rings are axially split. The construction material range from metal to TFE (tetra fluoroethylene). TFE lantern rings are usually filler with glass or with glass and molybdenum disulfide. They are inherently self lubricating and will not score the shaft. A throat brushing at the bottom of the stuffing box can be used to provide a closer clearance with the shaft to prevent packing extrusion.

Staffing Box Gland Plates
All mechanical packing are mechanically loaded in the axial direction by the stuffing box gland. In cases where leakage of the process liquid is dangerous or can vaporize and create a hazard to operating personnel, a smothering gland is used to introduce a neutral liquid at lower temperature. A sufficient quantity of quenching liquid should be used to eliminate the danger from the liquid being pumped. The neutral circulated in the gland mixed with the leakage and carries it to a safe place to disposal. Close clearances to the gland control the leakages of the combined liquid to the atmosphere. This quenches can also be used to protect the packing from any wear through abrasion, because the leakage cannot vaporize and leave behind abrasive crystal.

Gland packing are usually made of bronze, but case iron or steel can be used for all iron pumps. When iron or steel glands are used, they are normally bushed with a non sparking material like bronze.