Packed Stuffing Box
The packed stuffing box is the simplest type of shaft seal, Figure 1D.
It consists of a stuffing box cavity with a restrictive “throat” bushing at the pumpage end, several rings of packing, a hollow spacer or lantern ring, several more rings of packing and a follower or gland.
The lantern ring provides a point to inject external fluid in order to cool and lubricate the packing and provide better sealing in vacuum services.
A slight continuous leakage is required between the packing and shaft for lubrication.
Leakage ranges from 0.5 to 5 gal/hr (0.0019 m3/hr to 0.019 m3/hr) depending on fluid characteristics, pump mechanical condition and the type and adjustment of the packing. Compared to packing, mechanical seals offer the following benefits:
- Reduced worker exposure.
- Reduced product loss.
- Lower maintenance cost and effort.
- Fewer unplanned pump shutdowns for maintenance.
- Reduced fire potential.
- Reduced emissions.
- Reduced housekeeping.
- Reduced power consumption.
Packing is no longer recommended for hydrocarbon services primarily due to the continuous leakage required.
The only service for which packing may be required is firewater pumps.
The contractor is responsible for ensuring all pumps meet applicable codes and must add packing for firewater pumps if this is required.
Reference: Exxon Mobil