SEAL TECHNOLOGY S029
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.