Seal technology


The “best technology” phrase appears in recent government regulations and every day plant conversations.

So what is the best mechanical seal technology available today? Here is my opinion:

Start with the materials

  • Identifiable face materials compatible with the fluid to be sealed and any cleaners or solvents put through the lines.
  • Materials able to handle the full temperature range of the product you are sealing.
  • Viton┬« compatible with water.
  • Hard faces that are not sensitive to temperate change or caustic cleaners.
  • Unfilled carbon graphite seal faces
  • No elastomers sensitive to a shelf life.
  • No stainless steel springs or bellows. Use hastelloy “C” in stainless steel applications

The design is important.

  • The seal faces should close with spring and system hydraulic pressure. A seal should never blow open with a loss of or increase in system pressure.
  • Hydraulically balanced designs should be specified for low heat generation.
  • Specify two way balance in dual seal designs.
  • Use a built in pumping ring for cartridge dual seals.
  • Use the tandem configuration in dual seal designs. No rotating “back to back” designs.
  • Use the stationary configuration for non-cartridge applications.
  • Specify self-aligning designs for stationary cartridge versions.
  • The springs should be designed out of the fluid.
  • The elastomer should move to a clean surface as the faces wear.
  • Do not specify spring loaded elastomers.
  • Use only on-fretting designs.
  • The sealing liquid should be at the outside diameter of the seal to prevent solids from packing underneath the seal faces.
  • The seal design should be independent of the shaft tolerance and finish
  • Static elastomer should be located away from the seal face
  • Cartridge seals can compensate for thermal expansion and adjustments. Make sure the cartridge sleeve is sealed at wet end.
  • Provide vibration damping at the seal face.
  • The seal should be located close to the bearing.
  • Try to position elastomers away from the seal face if possible.
  • Make sure the stuffing box pressure keeps the lapped faces in compression.
  • Specify seals with a wide operating range
  • Look for low hysteresis features.
  • Make sure there is equal & opposite clamping of the stationary face to avoid distortion.
  • Be sure that the sealing fluid is located at the outside diameter of the seal faces
  • Leak detection capability is desirable
  • The seal should meet fugitive emission standards.
  • Simple installation is always desirable.
  • Eliminate all elastomers if possible
  • Try to use short seals. This will leave room in the stuffing box for a support bushing.
  • Finite element analysis of all components.
  • A method of supporting the shaft in the event of a bearing failure.
  • Trapped gaskets so they cannot “blow out” with pressure.
  • Position the seal as close to the bearings as possible.

There are a few other things to consider

  • Packaging that will allow the lapped faces to survive a one meter drop.
  • Back up sealing for dangerous and costly fluids.
  • A built in seal face vent for vertical pump applications.
  • No glued elastomers in split seal configurations.