CENTRIFUGAL PUMP PACKING
JAMES P. NETZEL
Packing is used in the stuffing box of a centrifugal pump to control the leakage of the
pumped liquid out, or the leakage of air in, where the shaft passes through the casing.This
basic form of a seal can be applied in light- to medium-duty services and to those liquids
that prove difficult for mechanical seals.
THE DESIGN OF PACKING RINGS_______________________________________
Packing may be referred to as compression, automatic, or floating. Each term describes the
type of operation in which the packing will be used.
Automatic and floating packings require no gland adjustments in controlling leakage.
Automatic packings are confined to a given space and are activated by the operating pres-
sure. Automatic packing rings are designed in the form of V rings, U cups, and O rings.
Floating packing includes piston rings and segmental rings that may be energized by a
spring. These types of packing are commonly used in reciprocating applications.
Compression packing is most commonly used on rotating equipment. The seal is
formed by the packing being squeezed between the inboard end of the stuffing box and the
gland (see Figure 1a). A static seal is formed at the ends of the packing ring and at the
inside diameter of the stuffing box. The dynamic seal is formed between the packing and
shaft or shaft sleeve. Under a load, the packing deforms down against the shaft, control-
ling leakage. Some leakage along the shaft is necessary to cool and lubricate the packing.
The amount of leakage will depend on the materials of construction for the packing, the
operating conditions of the application, and the condition of the equipment.
Packing must be able to withstand equipment variables (see Figure 1b). The design of
the packing ring and the materials of construction must be resilient to follow shaft runout
and misalignments, as well as to compensate for thermal growth of the equipment with-
out an appreciable increase in leakage.
FIGURE 1 Compression packing;