Page 76 - Valve Selection Handbook

Manual Valves 63

Figure 3-19. Stuffing Box with Lantern Ring.
(Courtesy of Babcock-Persta Armaturen-
Vertriebsgesellschaft mbH.)

A third variation of the stuffing box has a lantern ring mounted
between two packing sections, as shown in Figure 3-19. The lantern ring
is used mainly in conjunction with compression packings and may serve
four different purposes:

1. As an injection chamber for a sealant or an extruded or leached-out
lubricant.
2. As a pressure chamber in which an external fluid is pressurized to a
pressure equal to or slightly higher than the system pressure to pre-
vent any leakage of the system fluid to the outside. The external
fluid must thereby be compatible with the system fluid and harmless
to the surroundings of the valve.
3. As a sealant chamber in vacuum service into which an external fluid
is fed to serve as a sealant.
4. As a leakage collection chamber from which the leakage is piped to
a safe location.

The inclusion of the lantern ring, however, increases the depth of the
packing column. Sidewall friction reduces the gland packing input load
as the packing depth increases, leading to an impairment of the seal
37
integrity. Replacing the lantern ring with a spring is used in rotating
38
pump shaft seals to improve the seal integrity.