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.
- On February 17, 2018