How protector seals slash pump bearing failure rates
20 Sep 2018
With advanced retrofittable bearing protector seals readily available on the market, pump bearings failure should be the exception not the norm, says Chris Carmody of AESSEAL...
Huge advances have been made in the design and reliability of mechanical seals in the eighty years since they first arrived on the market.
There’s now a wide range of products which are proven to improve pump reliability and increase mean time before failure (MTBF), delivering swift return on investment and long-term operational savings.
This begs the question, why do operational managers continue to routinely use one of the least reliable sealing options available – the traditional lip seal?
More than half of all bearing failures on pumps are caused by contamination of the lubrication oil due to inefficient sealing - and the lip seal is one of the most common culprits.
Surface contact with the rotating shaft means lip seals start to deteriorate almost immediately after installation, allowing particle and fluid ingress into the bearings chamber, contaminating the lubrication oil and causing corrosion.
The impact of contamination can be significant. Research indicates that water contamination as low as 0.002% - a single drop of water in a typical bearing chamber - can reduce bearing life in some oils by as much as 48%.
Lip seals are a key cause of bearings failure [but] bearing protector seals are available which can eliminate the contamination that accounts for 52% of those failures
An oil-lubricated 45mm radial bearing running at constant load and speed under ultra-clean conditions (nc = 1) has been calculated to complete 15,250 operating hours. Introduce contaminated conditions where nc = 0.02 and its operational life plummets to just 287 hours - a dramatic decrease in MTBF.
In worst case scenarios, lips seals also cause wear to the shaft or shaft sleeve, requiring expensive repair or replacement.
Most maintenance teams are well aware that lip seals are a key cause of bearings failure and that bearing protector seals are available which can eliminate the contamination that accounts for 52% of those failures, and which can be retrofitted onto equipment.
But when MTBF can be as short as a couple of weeks it’s easy to see how the habit develops to keep using the same sealing methods when the product is already on the maintenance shelf, is relatively cheap and has been installed so many times you could virtually do it with your eyes closed.
However, the argument for changing habits and investing in modern, labyrinth style bearing protector seals is strong. These facilitate the ‘breathing cycle’ required by rotating equipment, allowing the oil/air mixture to move through the bearing seal out into the atmosphere when it heats and expands with the rotating equipment, then sucking it back into the bearing housing as it cools.
But while lip seals allow contamination to be sucked back in along with the air from the external atmosphere, protector seals use the centrifugal force of the rotating equipment to open a temporary micro gap, which immediately closes when the equipment stops rotating, forming a perfect seal against potential contaminants.
Lip seals may seem the cheap and easy option, but it’s important to consider that protector seals require minimal maintenance and provide protection until bearings reach the end of their natural lifespan – offering a MTBF of years compared to weeks.
For companies with a commitment to both reliability and the bottom line, upgrading to advanced bearing protector seals really should be a no-brainer.
Chris Carmody is special products manager at AESSEAL