SUBJECT: Why don't good seals wear out? 9-9

We know that a mechanical seal is supposed to run until the carbon wears down, but our experience shows us this never happens with the original equipment seal that came installed in the pump. We buy an expensive new mechanical seal and that one doesn't wear out either. What is wrong? Was the new seal a waste of money?

Not really. You are doing something that appears logical, you are trying to solve the seal problem by purchasing a different seal, but that is like trying to get a good paint job on an automobile by buying a good brand of paint.

If you wanted to get a good paint job on an automobile you would have to do four things and purchasing a good brand of paint is only one of them.

Here are the things you would have to do in no particular order:

If you did those four things correctly, how long can a paint job last on an automobile? Obviously for years. Step outside and watch the cars go by and you will see evidence of people that are not doing those four things. In fact it is so rare that when we see an older car that looks good, we stare at it.

Getting good seal life involves four steps also. They should be obvious, but let's look at them any way.:

We will look at each of these subjects in detail and hopefully begin to increase the life of our mechanical seals to the point where most of them wear out. We will be discussing seals for centrifugal pumps in this paper, but the information applies to just about any kind of rotating equipment including mixers and agitators.

Prepare the pump for the seal

Purchase a good seal

Install the seal correctly

Take care of the seal

Does any one ever do all of these four things? Unfortunately not. If we did, eighty five or ninety percent of our seals would be wearing out rather than the ten or fifteen percent that wear out now. The prematurely failed seal with plenty of carbon face left, continues to be the rule.

The most common excuse we hear to explain our lack of good seal life is that there is never time to do it right, followed by the cliché, "but there is always time to fix it". Most of us do one or two of the necessary steps and experience an increase in our seal life. There is nothing wrong with an increase in seal life, but that is a long way from wearing out seals.

Think about it for a minute. If the seal is lasting a year, how big can the problem be? The temperature cannot be too high or the pressure too severe. If that were true it wouldn't take a year to fail the seal. The product can't be too dirty for the same reason.

We often find the problem is as simple as a seal design that is fretting the shaft, causing a leak path through the damaged sleeve or shaft. Other times we find that the flush that is used to clean the lines once a year is the culprit, and no one is changing the seal materials to reflect this threat to the seal components.

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