Pump Reliability 17-01
Reliability is one of those buzzwords that academics love to use. We set up reliability programs and sometimes go so far as to hire reliability engineers. Vibration analysis, dynamic balancing and laser aligning equipment is purchased and company computers are re-programmed to record your progress. Maybe you’re purchasing seals and bearings to some standard and think that the standard is giving you a built in protection?
Have you joined the bandwagon? Are you purchasing to a company or engineering standard of some type and made the capital investment in the reading and recording data? Well, How are you doing?
Did you say, “Good, we’re making real progress?”
You’re full of baloney!
Let’s talk about pump reliability. Just what is it? Any discussion about pump reliability has to contain three elements:
- You must have a clear picture of what life you should be expecting from the pump. Don’t confuse that life with your past pump history. You’re probably getting lousy life now.
- You must maximize the life of the pump components. They should be wearing out not failing prematurely. Unlike the airlines, you should not be replacing seals and bearings just because they have a certain number of running hours on them. The shut down and labor cost of replacing parts is high.
- You must not experience any unexpected failure of the pump. In other words, you really do not want to run the pump until failure because that will always happen in the middle of a batch.
OK let’s take a look at those three requirements:
The two items that have the highest probably of failing your pump are the mechanical seal and shaft bearings.
- If you are experiencing corrosion of the wet-end of the pump, or getting excessive wear of the impeller and volute, you should be looking at different pump materials. Duplex metals combine wear resistance with corrosion resistance. There are plenty of people that can help you select the correct materials for those components
- Cavitation problems can be stopped if you have anyone around that understands cavitation.
- Pipe strain and alignment problems can be cured using simple shop practices.
- Most problems associated with operating the pump off its BEP can be resolved by teaching one or more of your people how to correctly size a pump. Once someone learns how to do this you will end up with smaller and lower cost pumps than the ones you have now.
Seals and bearings account for 90% of your premature pump failures. So how long should seals and bearings last?
- Seals should run until the sacrificial carbon face is worn smooth. Take a look at the seals coming out of your pumps and you will see plenty of carbon face material left. You could easily double or triple the life of your present seals. How long were the seals in there and how much carbon is left? You don’t need any more information than that.
Please do not point out that you are using two hard faces and cannot use this indicator of seal life. In most cases you should not be using two hard faces any way. The only justification for using two hard faces is that your product attacks carbon or you are afraid of a color contamination problem and your company does not allow anything black in the system. Pumping abrasives or slurry is not a good reason. Abrasives and slurries cannot penetrate between lapped seal faces unless they open. Go find out why the faces are opening!
- Bearings should last for their L10 life. Check with your pump supplier. The B10 life of most centrifugal pump ball bearings is in the order of a few hundred years, and we both know you’re not getting that kind of life.
Do we know why seals and bearing fail prematurely? Of course we do!
- Mechanical seals fail for only two reasons. If you damage a component (the damage can be either corrosion or physical damage), or if the lapped seal faces open.
- Bearings fail for two reasons also. Contamination and overheating. Water contamination is the main contamination problem and over-lubrication is the major cause of bearing over-heating
We can come up with a lot of reasons why seal materials are damaged or lapped faces open and that is what education is all about. It’s the same with bearing contamination and overheating. Educate your people and your pump reliability will increase dramatically.
Are you addressing these two problems of premature seal and bearing failure? Of course you’re not. I’ll bet you’re negotiating with your present seal and bearing suppliers to purchase these same failing seals at a lower price.
Once you get to the point of having 90% of your seals wear out instead of failing prematurely and you start to approach the L10 life of your bearings, we can then discuss how to prevent the unexpected failure.
We have to start somewhere, so let’s learn how to maximize the life of seals and bearings first.