Disaster bushing information

[Mikelauw]

I am doing some research into disaster bushings. What I am struggling to find is whether or not they are primarily manufactured by the OEM supplying the seal, or if there are a handful of companies just making these things. Also, if anyone has any info about what these things cost, that would be great.
Thanks.

 

[JJPellin]

I have never heard of a disaster bushing made by anyone other than the seal OEM. All of the ones I have seen are built into the seal gland and integral to the cartridge seal. The additinal cost is included with the seal cost, so I have never seen a breakdown of the extra cost of the bushing. If the bushing is just a fixed brass bushing, it probably only adds a couple hundred dollars. For a floating carbon, PEEK or other exotic material, the cost could be much more. I would suggest that you contact any major mechanical seal manufacturer that specializes in API seals (John Crane, Flowserve, etc.) and they should be able to give you some idea of the incremental cost.

 

[Mikelauw]

Thanks JJPellin. I saw you had mentioned disaster bushings in another thread, so I was hoping I would hear from you. We are actually already working with Flowserve, JC, etc... in other areas. We provide composite bushings and wear rings from PEEK and other compsites. Your answer confirmed what I feared was true. That these components could only really be priced out based on material, since it is simply part of a component, and never really has an individual price. In your experience have you had any significant problems with them? We had heard that some people had problems with the carbon bushings fragmenting in the seal and causing damage.

One other quick thing, out of curiousity, what have you heard about about PEEK disaster bushings? I was not aware of anyone already doing this.

Thanks a bunch!

 

[JJPellin]

After speaking to our mechanical seal engineer, I found that we have not used PEEK or comparable materials in disaster bushings. We have used brass, solid carbon rings (pressed into the gland), floating carbon rings (loaded with a wave spring) and segmented carbon rings (held together with a garter spring).

We have seen some failures associated with disaster bushings, but I believe all of them were really the victim of some other failure; either a bearing failure or an installation error. I have seen solidly mounted brass bushing rub on the sleeve so hard that they collapsed the sleeve onto the shaft and it had to be cut off. I have seen carbon bushings broken, but I think this was a result of incorrect installation or catastrophic bearing failures. So, I don't recall every faulting a disaster bushing for a pump failure.

 

[Mikelauw]

I see. I think the aspect that we are trying to understand is that after the seal has a problem and the disaster bushing has to be used, i.e. there is a serious problem, that the carbon bushings can actually fragment inside and cause additional damage. Not sure if you have encountered this or not. The way I understood it is that these bushings are only designed to last a short period of time(hours). Pretty much enough time to shut down the pump and prevent serious damage. The bushing is designed to sacrifice itself in order to save the seal. At least that is how I understood it, then again this is a new component to me and I am still earning.

Thank you for looking into this with me. I appreciate you enlightening me here!

 

[JJPellin]

I work in an oil refinery. Most of the products that we pump are flammable. In our pumps, I consider a disaster bushing as a safety / environmental risk reduction. In the event of a complete seal failure, I would hope that the disaster bushing would reduce the amount of leakage to reduce the chance of a fire, reduce the fuel to a fire, or reduce the potential impact on the environment. If our operators are diligent, it should only have to function for a few minutes.

 

[Mikelauw]

Ok, great. So when a bushing fails, who do you get a replacement from? Is it from the OEM? Or do they send out a team and overall haul the entire assembly and give you one bill for the whole thing?

If I am pulling you off in the wrong direction, please let me know. You have been very helpful, and I don't want to take advantage. It is hard to gauge in text whether people mind being helpful or not. In any case, thank you.

 

[bingopin]

As pointed out, the disaster bushing is a safety feature to limit the amount of leakage if the mechanical seals suffers some type of catastrophic failure such as a broken face. They run at a relatively close clearance to the shaft or sleeve, typically 10 to 15 mils if fixed. Floating type carbon bushings can run much closer clearances. I have only used bronze and carbon materials except for one application of Kynar in an acid pump. More and more we are going to the floating type bushing which allows for radial movement.

My experience is that disaster bushings are replaced when the seal is replaced and are always supplied by the seal OEM. If the seal is in the cartrige form, the bushing will be included and can be considered integral to the seal assembly. I don't know how you could diagnose a failed disaster busing without having the seal disassembled, which would very likely mean the seal will be replaced.

 

[JJPellin]

Bingopin hit the nail on the head. This is part of the cartridge seal. For any failure we replace the entire seal cartridge and the disaster bushing comes in the new one. I would never see a price breakdown of the cost of just the bushing. We stock complete seal cartridges in our warehouse and send them back to the manufacturer for repair and testing. No repairs are done on site.

 

[Mikelauw]

OK, that makes sense. I think this is all starting to come around for me. If you have any more insight, I'd love to hear it, but I think at this point I have a pretty good understanding of what is going on.

Thanks again JJPellin and bingopin!