In order for the packing to seal against a rough packing box bore requires excessive compression of the
packing. This over compression of the packing will lead to premature wear of the shaft or shaft sleeve.
On small pumps, the shaft runout at the packing box should be checked by manually rotating the shaft and
measuring the runout with a dial indicator. In most cases, total indicated runout should not exceed 0.003
inch. If the runout is excessive, the cause should be found and corrected. Bent shafts should be replaced
and misalignment corrected.
There are a number of different types of packing available, so when choosing new packing, care should be
taken to ensure that it is the correct size and type for the intended application. All of the relevant
conditions the packing will operate under, such as shaft size and rotational speed, must be considered.
Installing the wrong packing can result in excessive leakage, reduced service life, and damage to the shaft
The new packing should be installed with the joints staggered 90 degrees apart. It is sometimes helpful to
lubricate the packing prior to installation. The packing manufacturer should be consulted for
recommendations for a lubricant and for any special instructions that may be required for the type of
packing being used. With all of the packing and the lantern ring in place, the packing gland should be
installed finger tight.
There should be generous leakage upon the initial startup after the installation of new packing. The
packing gland should be tightened evenly and in small steps until the leakage is reduced sufficiently. The
gland should be tightened at 15- to 30-minute intervals to allow the packing time to break-in. The
temperature of the water leaking from the packing should be cool or lukewarm, never hot. If the water is
hot, back off the packing gland.
Mechanical seals are used in both pump and turbine applications. Mechanical seals
allow very little leakage and can be designed to operate at high pressures. Properly installed mechanical
seals will have a long service life and require little maintenance.
Basically, a mechanical seal on a small pump consists of a stationary and a rotating member with sealing
surfaces perpendicular to the shaft. The highly polished sealing surfaces are held together by a
combination of spring and fluid pressure and are lubricated by maintaining a thin film of the fluid sealed
between the surfaces.
There is a wide variety of mechanical seals available for small pump applications, each having its own
distinct installation procedure; therefore, it is important to follow the seal manufacturer's installation
instructions as closely as possible. The manufacturer should also provide information of the allowable
shaft runout and endplay for their particular seal.
Mechanical seals used in hydraulic turbines and large pumps consist of sealing segments, usually made of
carbon, held against the shaft by spring tension and lubricated by a thin film of water. These seals usually
require grease lubrication prior to start up if the unit is shut down for extended periods.
Since mechanical seals are precisely made and rely on very tight tolerances in order to operate successfully,
a great deal of care must be taken during the installation. Just a small amount of dirt or other contaminants
on the polished sealing surfaces can allow leakage past the seal and reduce the seal's life.