Life Span For AHU Motor Bearing

Bearing life is expressed in number of Revelations example 10000000 revaluations provided bearing is installed and maintained as per bearing manufacturer's recommendations.

crm

There are soooo many variables to affect the life span of bearings that I won't get into it for the moment. Each bearing will have a different life span. The best way to get the most life out of a bearing is to first select the correct bearing for the job, maintain it according to the manufacturers recommendations, and monitor its condition with vibration analysis. The vibration will indicate when it is starting to wear out.

Once the bearing is installed and at normal running speed & temperature, have a vibration meter print out a graph for a base line signature. Check the same bearing at least once a month and compare the new graph with the old one. After you note a change in the vibration graph you can begin to 'predict' when the bearing will fail. The instructions on using the vibration analysis equipment can fill in the details.

Many happy revolutions!

BDM

Replacing the bearing every 5 years is an effective method of preventing downtime, if it has proven adequate in the past, but it is not the most efficient and economical method

Bearing manufacturers do have charts that predict the lifetime of bearings based on load,temp, and Rpm,however, this is just an average, and not an absolute value.Radial load and axial load can affect the outcome drastically.Vibration anaylysis is the best predictive method for bearing life and equipment for this purpose has become relatively inexpensive and sophisticated with a very rapid learning curve.

A rough rule of thumb illustrates the importance of the proper belt tightening:

If you double the RPM of a bearing, you reduce life by 10%.

If you double the load on a bearing, you reduce life by 90%.

There are many other factors affecting bearing life,including proper lubrication and environment, but that is beyond the scope of this reply, unless you are extremely inquisitive .

Way too many variables to give a simple yes-no answer as others have noted.

5 yrs x 8760 hrs/year = 43,000 hours on the bearing. Bearing life depends on how bearing was selected, used and maintained. If correctly sized, gently used and well maintained, a bearing should last over 10 years without replacement.

If the AHU runs 24/7 with no more than 2 to 10 stoppages during a year, and is a clean environment, I would consider this gentle usage. If the bearing starts and stops several time per day in a dirty, hot environment, the duty is more severe. If no one has looked at or serviced the bearing in 5 years, it might be a candidate for replacement.

If bearing runs hot or runs "rough" pro-active replacement may be advised instead of cataastrophic failure. Depending on bearing, hot would be 20-40 degreees above ambient conditions. "Rough" could be subjectively felt on the finger tips, or heard as a noisy bearing. I have seen tables that combine vibration with bearing speed to quantify "roughness", which can help if you have rudimentry vibration equipment.

Yes there are many variables

-what type of bearing. Sleeve, roller, ball?

-operating environment it is exposed too. Humid , corrosive, etc.

-maintenance schedule

-size of motor and rotational speed

I have seen motors that are older than fifty years using the original manufacturers bearings, and some that don't make it past a few years

I too, have seen bearings last for decades.I replaced a bearing in the front (pulley end) of a 100 HP 850 RPM motor that drove a piston type compressor.The front pulley on this compressor was about 3 feet in diameter, and drove a single piston compressor(Gardner Denver).

The replacement bearing was in the spare parts locker in the compressor room.The locker was covered in undisturbed dust and cobwebs and probably had some of the original fallout from the open air atomic testing from the 1950's.There was also a perfect skeleton of a rat of unknown vintage.Must have gotten in at the factory before shipping.

When I opened the box, it was wrapped in brown wax paper, and cosmoline.The manf. date on the box was 1949, same as the motor and compressor.The original bearing had not failed but had become noisey, so it was replaced.The replacement, like the original, had brass retainer rings around the balls and was obviously built to last.

Engineers claim that the new retainers made of composites are just as good, but 60 years is a tough act to follow.

There was a lot of what I call "GORILLA ENGINEERING" back then,when a lot of fudge factor was built in to ensure against what, back then, were unknown factors.Now more factors are known, and the bearings are engineered more efficiently, more precisely, but with a narrower tolerance for abuse.The result is more bearing failures, more sales for the bearing companies, and ultimately, less efficiency when looking at the overall cost.

IMHO