date stamped on the package to help you determine the
shelf life of the packing. If a package has become
unsealed, reseal it. Better yet, ensure the packing is
used before its expiration date.
Packing requires frequent inspection and
adjustment, particularly while the pump is in operation.
The gland nuts must be adjusted with care, so ail the
packing is compressed evenly and equally around the
joint. If not, excessive and uneven wear of the packing
can result, and the rotating or sliding shaft could
become scored or grooved.
When a pump is first started, lubrication of the
packing may be relatively poor. Because of initial
friction, the packing may heat up and expand, thereby
compressing itself around the joint and further
reducing lubrication or leakage. Merely loosening or
backing off the gland nuts is not always the best
solution, because the liquid pressure in the pump can
force the complete set of packing to move outward in
the stuffing box. In this instance, the pump has to be
shut down and the stuffing box allowed to cool.
Several restarts may be necessary before the stuffing
box runs cool.
Additional packing procedures are too extensive to
be covered here. The primary purpose of this
discussion of packing is to alert you to the importance
of this pump component. It has been said that the
proper inspection, adjustment, and upkeep of the
packing are the most abused aspects of pump operation
Another important aspect of pump operation and
maintenance is the understanding of mechanical seals.
Mechanical seals are rapidly replacing conventional
packing as the means of controlling leakage on
Pumps fitted with mechanical
seals eliminate excessive stuffing box leakage that
results in pump and motor bearing failures and motor
winding failures. Mechanical seals are ideal for pumps
operating in closed systems, such as air-conditioning
and chilled water systems.
Type 1 mechanical seal is shown in figure 6-20.
Spring pressure keeps the rotating seal face snug
against the stationary seal face. The rotating seal and
all of the assembly below it are affixed to the pump
shaft. The stationary seal face is held stationary by the
seal gland and packing ring. A static seal is formed
between the two seal faces and the sleeve. System
pressure within the pump assists the spring in keeping
the rotating seal face tight against the stationary seal
face. The type of material used for the seal faces
Figure 6-20.Type 1 mechanical seal.
depends upon the service of the pump. Most water
service pumps use a carbon material for the seal faces.
When the seals wear out, they are replaced. New seals
should not be touched on the sealing face because body
acid and grease cause the seal face to pit prematurely
Mechanical seals should be replaced whenever the
seal is removed for any reason or whenever the leakage
rate exceeds 5 drops per minute.
Mechanical seals are positioned on the shaft by
means of stub or step sleeves.
should not be positioned by the use of setscrews. Shaft
sleeves are chamfered on outboard ends to provide
ease of mechanical seal mounting. Mechanical seals
ensure that positive liquid pressure is always supplied
to the seal faces and that the liquid circulates well at the
seal faces to minimize the deposit of foreign matter on
the seal parts.
Figure 6-21.Stuffing box on centrifugal pump.