The major improvements in mechanical seals in recent years
Where have we been, and where should we be going? You have been
using mechanical seals for many years now. Over the years you have
witnessed many design changes, but has there been any real
improvements in seal performance, or is your increased seal life
coming from the use of environmental controls such as flushing,
quenching and the use of jacketed stuffing boxes?
In this paper I am going to attempt to list the most significant
improvements in the basic design of mechanical seals and give you
some ideas as to where the sealing industry should be spending their
Here are some of the advancements that have been made that
contribute to longer mechanical seal life:
- The general acceptance of hydraulic balanced
seal designs that eliminated a major source of unwanted heat
at the seal faces.
- Stationary seal designs
that reduced the problems associated with the lack of stuffing
box to shaft squareness.
- The use of O-rings that reduced the problem of sliding dynamic
- Self-aligning seal faces that made the sealing of horizontally
split pumps practical.
- Cartridge seal design that solved a lot of the seal failures
caused by improper seal installation, shaft thermal growth and
open impeller adjustment.
- Unfilled carbon seal faces that eliminated most of the
chemical compatibility problems we had sealing process pumps
- A special grade of Dupont's elastomer Viton® that has a
reasonable amount of water sealing capability
- Chemraz and Kalrez. The wonder compounds of the 1970s that
allowed mechanical seals to be chemically compatible with just
about any fluid.
- The creation of alpha sintered silicon carbide hard faces that
are not only corrosion resistant to most fluids, but also
excellent conductors of heat.
- The elimination of Teflon in many original equipment seals.
Teflon was the main contributor to shaft
- Non fretting seal designs that eliminated the need for sleeved
- Welded metal bellows designs that eliminated the problems of
elastomers in cryogenic and non-petroleum, high heat
- Split seal designs that
eliminated the last reason for using packing in pumps.
- Finite element analysis techniques that allow us to design
small cross-section seals with high-pressure capability.
- The use of suction
recirculation piping along with an oversized stuffing box to
eliminate most of the problems associated with the sealing of
What will you need in future years?
- The elimination of elastomers in process seals, not only
because of elastomer temperature limits, but the more serious
problem of chemical compatibility with both product and flushing
fluids. Someone has to pick the correct elastomer and there is
always room for error.
- Seal designs that can take excessive axial movement without
changing their face load.
- The elimination of barrier or buffer fluid between dual
mechanical seals. Present gas designs are not filling this
- Temperature control in the stuffing box area without the use
of water or steam. In many applications the fluid in the stuffing
box must be kept within certain temperature limits to prevent it
from changing into a sold or a gas.
- Instrumentation to predict pump cavitation, excessive shaft
deflection, high heat, etc.
- Reliable non-stick seal surfaces to prevent solids from
adhering to the sliding seal components
What is the reason for the increased seal life we are experiencing
- A better educated consumer. Many of the mechanics and
engineers have received specific seal and pump training.
- The wide use of cartridge
seals that has made installation easier and less error
- The oversized stuffing box.
- Suction recirculation piping that has eliminated many of the
problems associated with the sealing of slurries.
- The demise of unbalanced seal designs.
- Better motor/ pump alignment
ever since the popularity of laser aligning.
- The more common use of environmental
controls in the stuffing box area.
For information about my CD
with over 600 Seal & Pump Subjects
Link to Mc Nally home page