Maintenance personnel usually dislike rotary seals. This is because replacing a low-cost oil seal requires dismantling a whole piece of equipment. If an employee sees a leaking reducer, the first step is to stop the reducer because of safety concerns. The next step is less clear. It is impossible to remove and replace the old seal with a new one because maintenance access is blocked by a shaft. The employee must shut off the line, separate the reducer from the connecting equipment, pull the cover off the shaft, find the old seal and pull it off the shaft. Finally, the employee can install a new seal, but now he or she must put the equipment back together in the opposite sequence. This process will likely take a few hours. If the shaft is more than one meter in diameter, the procedures could require several days. The cost varies based on the facility, but whatever the cost, it is far greater than the approximately $10 value of the oil seal.
The double-lock, double-ring designs seal oil and other fluids more effectively than their single split counterparts.
04/01/2015
Image 1. Single split seal (Images and graphics courtesy of AIGI)
Images 2 and 3. A split seal is applied in large equipment.
Image 4. Split bearing protector
For example, consider the ball and socket design. It consists of two rings made of either the same or different materials. The outer ring is bound by a spring while the inner ring is energized by another spring. Both the outer ring and the inner ring have a split cut. Normally, one split is at the 5-minute position and the other at 55-inch clock position during installation (see Image 3). As shown in Image 4, when the split is pulled apart and viewed horizontally, the ball will stop the leakage path. When viewed from above, the inner ring will stop the leakage path. Together, they overlap the split, both horizontally and axially. The effectiveness of this overlap is not just theory but has been tested in laboratories.
Table 1. Testing Report # MF-130710, Testing Standard: ISO 6194-4-2007
Image 5. The positions of the splits on the double split seals
The best version of a split seal delivers performance not by a single split but by two very strange splits. Users who currently work with single split seals and want to improve performance should consider a double split option. Understandably, users who have never had split seals on their large equipment may be concerned about cost.
Compared with the price of an oil seal, the double-ring, double-lock split seal is more expensive. The price is higher because this product has to be manufactured from anti-relaxation polymer material and some special cutting tools, and it has undergone extensive research and development.
This split seal design, however, will cost almost nothing in comparison to the cost of installation and saved production time. In fact, it will practically pay for itself.