Page 287 - The Tribology Handbook

625 Packed glands

The main applications of packed glands are for sealing the stems of valves, the shafts of rotary pumps and the plungers of
reciprocating pumps. With a correct choice ofgland design and packing material they can operate for extended periods with
the minimum need for adjustment.

VALVE STEMS

Valve stem packings use up to 5 rings of packing material
as in Figure 25.1. For high temperature/high pressure
steam, moulded rings of expanded graphite foil material
are commonly used. This gives low valve stem friction.

Figure 25.1 A typical valve stem packing

To reduce the risk of extrusion of the lamellar graphite
DISC SPRING
during frequent valve operation, the end rings of the STACK
packing can be made from graphite/yarn filament.
Materials of this type only compress in service by a STUD SPACER
small amount and can provide a virtually maintenance SLEEVE
free valve packing if used with live loading as shown in
Figure 25.2.
BRAIDED
GRAPHITE
EXPANDED
GRAPHITE
BRAIDED
GRAPH IT€

Figure 25.2 A valve stem packing using spring
loading to maintain compression of the valve
packing and avoid leakage

ROTARY PUMPS
GLAND FOLLOWER LIQUID
Rotary pump glands commonly use up to 5 rings of
packing material. For most applications up to a PV of
150 bar m/sec (sealed pressure X shaft surface speed) a
simple design as in Figure 25.3 is adequate. In most
pumps the pressure at the gland will be 5 bar or less and
those with pressures over 10 bar will be exceptional.
At PV values over 150 bar m/sec direct water cooling or
jacket cooling are usually necessary and typical arrange-
ments are shown in Figure 25.4 and 25.5.
When pumping abrasive or toxic fluids there may be a
need to provide a flushing fluid entry at the fluid end of the
glands, as in Figure 25.6, or a high pressure barrier fluid
which is usually injected near the centre of the gland as in
Figure 25.7.
Figure 25.3 A general duty rotary pump gland
625.1