Causes of overheating in cartridge mechanical seals
Too much heat can cause multiple problems with mechanical
- The elastomer (rubber part) can be damaged.
- Some seal faces can be damaged.
- Carbon-graphite faces can pit as trapped air expands within
the carbon, or the product carbonizes and pulls out
pieces of the seal face.
- Plated faces can heat check and crack causing rapid
carbon face wear.
- The filler in some carbon /graphite compounds can
melt or oxidize at elevated temperatures.
- Critical dimensions can change causing the lapped
seal faces to go out of flat and leak prematurely
- The sealed product can change state and :
- Vaporize between the faces opening them.
- Crystallize on the moving components, restricting
- Change fluid viscosity restricting the
ability of the seal to follow run
- Solidify, making the seal inoperable.
- Build a film on sliding components and
the lapped seal faces.
- Carbonize or coke restricting the
seal movement and opening the
- Corrosion always increases with
Some heat problems are not seal design or seal installation
- An inefficient heating or cooling jacket on the pump.
- A layer of calcium or some other similar product has
built up on the jacket walls, interfering with the heat
- The coolant is flowing too rapidly through the cooling
- A thermal bushing was not located in the bottom or
end of the stuffing box.
- If steam is being used as the coolant, the pressure
is too high.
- The fluid is not "dead ended" in the stuffing
box. There is either suction or discharge recirculation
of the pumping
- Clearance between the seal outside diameter and
the stuffing box bore is not sufficient.
- The shaft material is conducting the product
heat to the cartridge static elastomer and
As an example: carbon
steel conducts heat much better than a stainless
- The dual seal convection tank is not convecting.
- The convection tank is running backwards.
- The dual seal barrier or buffer fluid has
been shut off.
- The quench has failed.
- The product has a low specific heat
and poor conductivity. Oil is a
- The seal faces were over-compressed
during the installation process.
- A wrong installation measurement
- The mechanic did not read,
or understand the print dimension.
- The pump sleeve moved as
the impeller was tightened
- The measurement was taken
at the wrong place. The
stuffing box face
only safe reference
The cartridge seal design has a major affect on heat generation
and heat sensitivity:
- Unbalanced seals generate more heat than hydraulically balanced
- Two hard faces generate more heat than carbon/graphite
vs. a hard face.
- Silicone carbide and tungsten carbide dissipate heat
faster than 99.5 ceramic or carbon&endash;graphite.
- The location as well as the grade of the elastomer
can be critical in temperature sensitive applications.
- In dual seal applications, convection systems are
not as efficient as pumping rings or forced circulation
of the barrier fluid
system. When oil is used as a barrier fluid forced
circulation or the use of a pumping ring is mandatory.
The above problems are not unique to cartridge seals,
there are however some problems that are unique:
- Pushing the seal gland along the shaft and against the
stuffing box face can over compress the seal because of the
between the shaft and the cartridge sleeve static elastomer.
In dual seal applications the inner seal can over compress
as the outside seal looses some of its compression. Be
sure to reset the spacing device (usually "clips" of
some type) prior to locking the seal to the shaft.
- Some open impeller pump designs (Duriron as an example)
adjust to the back plate rather than the volute. Be sure
the cartridge seal after the impeller adjustment.
Cartridge set screws can slip on a hardened sleeve. The
system pressure can then over compress the seal.
- Higher pressure applications, or water hammer can move
the set screws and over compress the seal faces.
- Be sure to re-tighten the adjusting nuts after making
the impeller micrometer adjustment on those pump
that uses that type of
adjustment method. The Chesterton System #1 pump
is a good example of this design.
- Make sure the centering-positioning clips are in
place when installing or resetting the seal for