Pumps are routinely placed into severe duty applications where durability and reliability are critical. But, even the most expertly designed and stout pieces of equipment can be vulnerable to downtime and, eventually, failure in these challenging conditions if not maintained properly.
Proper lubrication and protection of the bearings are key factors supporting pump longevity. Without proper lubrication, failure is inevitable and leads to high-cost repairs, replacements, and downtime.
While there are many lubrication methods, there is one that has gained popularity and relevance for pumps in downstream applications, such as refining and petrochemical: oil mist. This lubrication method uses an aerosol mixture of fine oil droplets suspended in air. A secondary system takes oil from a supply tank and atomizes it into finer particles. That particulate mixture is then distributed to the bearings.
Oil mist has gained traction in downstream applications because it provides precise lubrication, which means less power consumption; less lubrication excess and waste; fresher lubrication coverage on the bearings; and better pump mean time between failures (MTBF).
BENEFITS AND PROMINENCE OF OIL MIST
While oil mist continues to grow favorably among pump operators, it presents sealing challenges. The main difficulty associated with oil mist is keeping it contained within the equipment. Because the lubrication particles are very fine, minuscule openings or leak paths can allow the oil mist to escape, impacting bearing life and operator safety. A leading cause of equipment downtime and lost production is bearing failure, and failed bearings occur predominantly by lubrication loss and contamination. Additionally, stray hydrocarbons can be inhaled or pool on surfaces and create potential fall hazards. Proper sealing selection is important to operator safety and equipment reliability.
The American Petroleum Institute (API) recognizes the benefits and prominence of oil mist, which is why most API pumps are oil mist lubricated equipment. Meeting the API standard–specifically API 610–means having bearing housings with one of two specific sealing solutions. It states that “bearing housings shall be equipped with replaceable labyrinth-type or magnetic-type end seals and deflectors where the shaft passes through the housing. Lip-type seals shall not be used. The seals and deflectors shall be made of spark-resistant materials.”
Additionally, the U.S. Environmental Protection Agency (EPA) has tightened regulations on emissions and other particulates. While regulation development is ongoing, operators are continually pressed to reduce carbon emissions and eliminate hydrocarbon leakage. As oil mist is an aerosol mixture, it is not always possible to detect leaks with the naked eye. Preventing leakage starts with having the right bearing seal technology in place.
A CUSTOM-MADE, RESILIENT SOLUTION
Bearing isolators are two-part compound labyrinth, or magnetic, seals consisting of a rotor and stator working in conjunction to protect rotating equipment from lubrication loss and contamination ingress. However, not all of them are the same. For oil mist, operators must be aware that bearing isolators are engineered to order, utilizing specialized materials, design concepts, and features to provide their application the right protection. The technology is not general or plug-and-play with any piece of rotating equipment. In the case of oil mist lubrication, the proper design of the bearing isolator will determine if the equipment is protected. There are several design criteria to consider when selecting a bearing isolator for oil mist applications.
Labyrinth-type Bearing Isolators
Bearing isolator, operators should make sure there is a coalescing ring, that blocks mist from escaping through the labyrinth, where it is collected and deposited back into the bearing housing through the lube return. Another essential component is a vapor-blocking, or VBX, ring. Bearing isolators depend on centrifugal force to operate; however, there are times when equipment needs to be shut down. The VBX ring ensures that the labyrinth path is shut off and no oil mist can escape while the equipment is at rest. During operation, centrifugal force provides lift so that it is still operating with a non-contact design.
The stator/rotor interface is another key piece of internal technology. Properly designed interfaces provide permanent IP66-rated protection against contamination ingress. A contamination chamber should also be a part of the bearing isolator’s design to collect contaminants trying to enter the bearing housing and expel them through the expulsion port using centrifugal force and gravity. Another important design element is the D Groove. As the name suggests, it is a D-shaped groove built into the rotor that captures oil on the shaft. The oil runs along the groove and is returned to the bearing housing.
Aside from its sealing and protection benefits, labyrinth-type bearing isolators also are known for their longevity. Because they don’t depend on contact as a sealing mechanism, this technology can last as long as the equipment. The VB45-U bearing isolator from Inpro/Seal is designed with these criteria in mind to create an effective oil mist seal for downstream operators.
Magnetic-type Bearing Isolators
This technology works differently but is still an effective choice for oil mist lubricated environments. Magnetic-type seals utilize two precision-lapped faces that are magnetically energized to create a liquid-tight seal. The critical element is ensuring that the seal is designed so that the faces maintain proper lubrication and that the face loading is distributed equally around the rotor and tuned specifically for oil mist.
Additionally, operators must take extra care while installing magnetic-type seals so the faces aren’t damaged. Flat faces are critical to maintaining a quality seal. Magnetic-type seals are a great choice for oil mist as positive contact seals effectively seal fine mist particles.
The Inpro/Seal VBMag bearing isolator is a magnetic-type seal perfect for oil mist lubricated pumps. Both labyrinth and magnetic-type bearing isolators do not cause shaft wear, a common problem tied to elastomeric lips seals, which can wear quickly at the contact point and damage the shaft.
CONCLUSION
Bearings are valuable components that support the proper functionality of pumps. Like any essential component, though, they require adequate protection. The best technology to guard against premature bearing failure is bearing isolators, and it is critical to select the correct bearing isolator design that incorporates features specific for oil mist lubrication. Selecting a general bearing isolator design may not ensure adequate protection and can result in lost lubrication and bearing failure, resulting in decreased MTBF and workplace hazards.
Chris Solfelt is the product manager for Inpro/Seal and can be reached at csolfelt@doverprecision.com. He has nine years of experience in the bearings and seals industry for rotating equipment, including five years at Inpro/Seal. Inpro/Seal is a world leader in the design and manufacture of permanent bearing protection and complete shaft sealing solutions for a variety of rotating equipment across multiple industries. For more information, visit www.inpro-seal.com.