What seal should I buy?
You're going to have to figure that one out yourself, but I can
tell you which designs not to buy:
- Purchase seals only when the materials are clearly identified,
because it's impossible to troubleshoot "mystery materials." It's
not good enough to know that the metal components are manufactured
from stainless steel. You should know which grade. They're not all
- Stainless steel seals should have "haystelloy C" springs, or
you will experience breakage problems caused by "chloride stress
- Buy only non-fretting designs. You do not need the shaft damage caused by many
- Keep away from spring loaded elastomers because they are the
main cause of fretting problems. When O-rings are spring loaded
that cannot flex and roll.
- Put the seal into the fluid. Centrifugal force will throw the
solids particles, in the fluid, away from the lapped seal faces.
Most outside mounted designs have this problem
- As the sacrificial carbon face wears, the seal components,
especially the rubber part, should move to a clean surface to
prevent hang up..
- Choose designs where there is no dynamic elastomer mounted on
a pump shaft or sleeve. Dynamic elastomers are sensitive to shaft
finish and tolerance.
- Do not purchase seals that have small springs exposed to the
sealing fluid. Springs can clog and open the lapped faces
- Cartridge design seals are easier to install and absolutely necessary when your
people adjust the pump's open or semi-open impeller.
- Check to see if there is a way to vent the lapped faces if the
seal is installed in a vertical pump. This can be a big problem
with the outboard seal in a dual seal application.
- Some seal designs are unidirectional. They run in either a
clockwise or counterclockwise direction, but not both. A double
ended pump needs both kinds.
- You do not want to use designs that require a special
lubricant on the rubber components. Many rubber bellows designs
have this problem
- If you are using a metal bellows design, be sure that the manufacture has provided
vibration damping to prevent bellows breakage.
- Some designs use a carbon face shrunk into a metal holder.
These designs often have trouble keeping the lapped face flat.
Also check to be sure that they have not glued the seal face to a
metal holder. Many fluids can attack these glues
- Be sure cartridge designs are sealed to the shaft at the
inboard end of the cartridge sleeve or you will find it almost
impossible to remove the cartridge when the space between the
cartridge sleeve and the shaft, fills up with solids.
- The seal should be able to seal both a pressure and a vacuum.
Any balanced seal can do this but some of the newer split designs have trouble in mixers and agitators that can shift
between a vacuum and a positive pressure.
- Mixers and agitator shafts experience a lot of radial
movement. Not all seals can handle this excessive travel. Check
that the design you are considering will do the job. Many seal,
companies build special seal designs that have wide hard faces and
extra internal clearances to compensate for this movement
- When choosing between a stationary (the springs do not rotate
with the shaft) and a rotary design always choose the stationary
version. Stationary seal designs are not sensitive to pump and driver misalignment
- Check that a spare part kit is available and that the seal can
be repaired without special tools or testing equipment.
- The latest seal designs have been run through a "finite
element analysis program" that allows the manufacture to build
thinner and shorter components with the same pressure capability
as the old and bulky "heavy duty" designs.
- You should use only hydraulically balanced designs because of their wide operating range.
- Some seal designs are loaded up with rubber components. Avoid
them if possible.
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Link to Mc Nally home page