What sealing methods have the highest MTBF?
This is a loaded question because there is always the caveat: it depends. The factors that dictate Mean Time Between Failure (MTBF) are vast and can change from application to application and even from pump to pump in the same plant doing the same job.
SealRyt has forged a philosophy of addressing each pump, each agitator, and each line shaft as an individual engineering problem to be solved.
With that being said, here are some general understanding of the lifespan for different rotating shaft seal methods.
Mechanical seals are critical to applications in which the pumped medium is considered toxic, corrosive, or explosive. Compounds classified to be hazardous or fugitive emissions also require advanced sealing methods.
Mechanical seals suffer premature failure when installed on equipment with mechanical issues. Deflection, run out, and other shaft stabilization symptoms can wreak havoc on the ultra-precision mechanics of lapped seals.
Slurry and high particle mediums can also take their toll on mechanical seals. Making sure that flush fluid is in balance using the correct pressure and flow rate is essential to seal longevity.
Properly installed and stabilized mechanical seals should get 3-5 years of useful service. If they are getting less, then they could be installed on worn equipment that needs shaft support, or flush fluid characteristics need analysis.
Stuffing box mounted bearings were first introduced in the early 2000s when SealRyt patented the PackRyt® Bearing System. Well known for their high-performance braided packing, SealRyt engineered a load-bearing, close clearance polymer that is machined to custom fit each stuffing box.
Bearings work similar to mechanical seals but without the ultra-precise, micron-level clearances. Bearings stabilize the shaft, reducing runout or wobble, bringing the shaft into concentricity. Bearing systems work in concert with packing to create a close clearance seal at the bottom of the stuffing box that stabilizes the shaft, then the braided packing is layered into the remaining space and compressed using the gland follower. The combination of shaft stabilization and close clearance fit provided by the bearing allows the packing to seal effectively and longer than packing alone. Bearings gain a leg up on mechanical seals because of their simplicity. They have no moving parts.
Bearings typically fail when flush or lubrication is interrupted for long periods of time. While bearing material is formulated to take an incredible amount of heat and stress they can fail after extended exposure.
Bearings are designed to run from rebuild to rebuild. On average they should last anywhere from 1 to 3 years of useful service.
Listed below are some examples of BEFORE and AFTER service records for bearing systems in different types of common process applications.
Modern braided packing is made from high-tech synthetic fibers weaved in complex patterns that create a square-shaped packing compressed into a stuffing box in layers. The packing gland is then tightened enough to create a seal but allows the shaft to rotate. Essentially, packing seals through both friction as well as hydraulic pressure break-down.
There is a wide variety of packing styles and configurations, and not all packing is the same. Generic packings generally are utilized in various common applications and in bid situations where low price is considered a requirement. They are effective for a while, then wear out/compress and need to be replaced. More advanced packing is designed for specific applications, higher reliability requirements, and a higher predictive quotient. When choosing packing consider these parameters: Temperature, Speed, pH, Media, and Safety. An engineered packing can be more expensive by the pound, but it lasts longer and saves on downtime and maintenance hours.
Braided Packing lifespan is varied. SealRyt engineers strive to double the current packing maintenance cycle by utilizing advanced braiding technology.