packing - lantern rings

[diesel421]

This is actually for a Lightnin mixer shaft rather than a pump shaft but it is the same concept.

We have a 1 1/2" Lightning mixer shaft with a set of braided square packing rings. We also bought a plastic lantern ring for $200.00. Recently, my boss found a brass lantern ring for $1,000.00.

Is a brass lantern ring better than a plastic lantern ring? What other kinds of lubrication arrangements can we make to make the plastic lantern ring last longer?

What are your experiences with plastic versus brass lantern rings?

Thanks

 

[diesel421]

i should add this is a low rpm application (200-400 rpm). we don't forsee the friction that packed centrifugal pumps typically experience but we could be wrong.

 

[Artisi]

Either lantern ring should be Ok- if the lantern ring is wearing something is radically wrong with the set-up - a lantern ring either plastic / nylon / brass etc should last forever.

More detail required as to the problem.

 

[quark]

I agree with Artisi. Lantern rings are not tight fitted to the shaft like packing rings. If you can use graphited packings, you can do away with lantern rings and lubrication.

 

[Artisi]

quark, I would say "you might be able to do away with the lanterns ring"

 

[quark]

I would have if it were pumps, but lubricating agitator shaft rings puzzled me, somehow (if lubricant dripping into the vessel is a problem).

We had this funny thing of replacing only the top three rings (in my first company, about 12 years back)whenever there was leakage. There were occasions when we had to cut the shaft and then lift the stuffing box because sledge hammers were too weak. I still remember that after changing the packings from asbestos to graphited PTFE/Aramid, things improved.

I would like to suggest the OP to look into mechanical seals, rather.

 

[JJPellin]

I agree that you should first verify if the packing ring is really needed. In many cases, the documentation with a machine includes generic drawings that show a configuration that might not be appropriate for your machine. All of our Lightnin' mixers use mechanical seals. As already noted, this would be a logical improvement. If you must stick with packing, understand how it is being lubricated. Do you inject clean fluid into the lantern ring connection? Do you periodically inject grease into this connection? If you don't add any lubricant, then I would eliminate the ring. If you do need it, verify that it is the proper dimension. It should fit closely to the bore of the packing box, but have ample clearance above the shaft. If the fit is such that the ring can drop down and rub hard on the shaft, then it is the wrong size. Next, verify that you are using the correct packing. Inappropriate packing could generate excess heat and degrade the plastic ring. Next, verify that you are installing the packing correctly. It is common to over tighten packing. Especially if the operators and mechanics are used to working with mechanical seals, they can have a tendency to try and stop the leakage completely. Packing has to leak.

One other point occurred to me. You need to be sure that the shaft is running true through the packing case. A shaft that is bent, rough or off center through the packing case could cause problems with leakage that could then cause you operators to over tighten the packing.

If you pass all these tests and still have problems, then I would purchase the brass ring. The plastic ring could be intended for clean cold service. It may be that your service is too hot, abrasive, corrosive, or chemically incompatible with the plastic ring.


Johnny Pellin