Chapter 10 - Pump Shaft Sealing

Abstract

Centrifugal and rotary positive displacement pumps have sealing arrangements to keep pump fluid from leaking where the pump shaft penetrates the casing. These sealing arrangements may be packed glands or mechanical face seals. Seals keep foreign material from entering the pump or lubricant from leaking out of bearings and transmissions. Reciprocating pumps have soft packings, molded elastomer rings, piston rings, and metal bushings. Most centrifugal and rotary pumps still have packings, but with mechanical seals becoming more reliable and economical, companies now use mechanical seals even in water services. This chapter also discusses packing glands. A packing gland works through compression. The rings are compressed with enough force to keep the pump fluid from leaking through the shaft. Even though the packing tings are either self-lubricated or grease lubricated, the pumped fluid adds to the lubrication and also cools the packing. Abrasive fluid or too tight a packing gland eventually scours the part of the shaft beneath the packing. To prolong the shaft life, manufacturers install replaceable shaft sleeves where the shaft comes into contact with the packing. The advantages of packings over mechanical seals are that the packings save money initially and are easier to install and replace.