Pump Packing and Mechanical Seals ByEr. Laxman Singh Sankhla
B.E.Mech., Chartered EngineerJodhpur, India Mail ID:
[email protected]
Packing and Mechanical SealsPacking fills the stuffing box
(Figure 2.13) to minimize the amount of leakage along the shaft by
sealing the clearance space between the shaft and casing. A throat
brushing prevents the packing from being forced into the eye of the
impeller by the gland follower.FIGURE 2.13STUFFING BOX
Packing is a soft, pliable material like cotton, asbestos, or
flax, usually woven or braided into a continuous square-shaped
strand. Packing is usually coated with graphite or Teflon for
lubrication. Because the packing is softer than the shaft, the
shaft can rub against it without damage. The graphite or Teflon
coating provides some lubrication, but additional lubricant is
needed to keep friction to a minimum.
Some fluid leaking out of the stuffing box is normal and
provides lubrication between the shaft and packing. In some cases,
packing is pressure lubricated by the use of lantern rings. Lantern
rings are perforated metal rings that surround the shaft between
layers of packing in the stuffing box. These rings allow additional
fluid from the gland sealing line to be injected into the stuffing
box for lubrication of the packing.
A gland follower fits into the open end of the stuffing box and
holds the packing and lantern ring in place against the throat
bushing. Adjusting pressure on the gland follower against the other
parts of the packing gland regulates the flow and leakage rate of
the fluid lubricant.
Although a large number of centrifugal pumps use braided packing
in stuffing boxes (Figure 2.14) mechanical seals have gained
acceptance in the petroleum industry They:
1. Require no leakage which is very important when pumping
hydrocarbons because of the potential safety hazard,
2. Last much longer than packing, and
3. Require less maintenance.
These are real advantages if the pump is in a hard to reach or
inaccessible location.
FIGURE 2.14MECHANICAL SEAL
There are many different types of mechanical seals available on
the market however, all mechanical seals have similar basic
components and operate similarly. A typical mechanical seal
consists of rotating parts attached to the shaft and stationary
parts secured to the seal plate, which is bolted directly to the
casing. The highly polished sealing faces of the rotating and
stationary parts are held in contact by one or more springs.
