Vee and all,

I have been looking into bearing isolators and am finding there is a older and patented design that is based on a single o-ring.

I see that there is a newer more recent innovation form across the pond that includes 2 o rings creating a wider surface.

Can you contribute anything to my research such as:

What failures do you find on these isolators?

Are the old style isolators still popular simply because they are written in to so many purchasing specs?

Is the dual o ring model really innovation in terms of performance (it makes sense to me - but that does not qualify it)?

Anything else you can add would be most appreciated.

Terry O

We have had success with INPRO seals on our large fans here.

Terry,
We have bearing isolators on pillow block bearings and motor end bells. They pillow block bearing style has 1 o-ring for rotor and 1 for stator. One style used some sort of o-ring for venting during operation and would seal when at rest. (Vapor block?) Either style worked great. The pillow block style with oil lubrication became an issue when the oil level was not properly maintained. It would leak as the return port became flooded. Training the PM crew help resolve that problem. I see the types that are on motors with greased bearings but whenever inspected it appears the grease is not leaking out but not sure if it may be going in the windings. End bell stays clean.

Old style worked well and the expense to change may be a factor.

Why would 2 o-rings be needed? Seems redundant.

I haven't heard of two designs... all I have heard of is Inpro.

The seal would have a rotating part (rotor) and stationary part (stator). The O-rings would seal between the seal stator and the machine stator... and between the seal rotor and the rotating shaft. To my way of thinking these O-rings should not be a challenging part of the seal design since the O-rings are applyied between parts that do not move relative to each other. The unique and challenging part of the design would seem to be the interface between rotating and stationary parts of the seal which of course must be non-contacting, but still need to provide a tortuous path for leakage.

What is supposed to be the relative benefits of the two designs?

Thanks for your replies.

Disclaimer: I am only beginning my education in this area – so please appreciate this is coming from a student. I am hoping you will set me straight or confirm as we have interest in this issue and want to be accurate. Obviously vendors of each of these systems have told me all about how great they are. I am trying to learn where we can make improvements in best practice.

A single O-Ring at operating speed is fine. However as your machine slow-rolls or accelerates to operating speed, its dynamic O-ring will scrape on the sharp edges of one of the two grooves, thus damaging the O-ring (and its vapor blocking capability).

With the dual O-Ring its large cross-section shut-off ring contacts a wide and well-contoured surface and because pressure = force divided by area, there’s low pressure at worst, and no pressure at best.

At standstill, no fluid passage is possible between the vapor space inside a bearing housing and the external region or other atmosphere on the outside.

This would seem to make it a better solution but I want to make sure I have that right.

I think all machines are subject to starting up and shutting down, some more than others. Is my assumption about the single O-Ring scraping correct.

With the dual O-Rings, there is little if any risk of rotor-stator contact because the mass-symmetrical rotor is clamped to the shaft with two O-rings.

Make sense?

Terry O

Terry et al,
I am responding since you asked me specifically. My knowledge on this topic is limited, so I will refrain from comment.

Thanks Vee.

Now you have me wondering if bearing isolators are used much outside the USA.

Anyone?

Terry O

Terry,

Perhaps the hangup is related to terminology. I have never considered a "bearing isolator" anything more than a "seal for brearings". I guess only a product vendor can call it what they want.

Walt

We are moving away from Inpro isolators here because in our applications they use RTV to seal against the pillar block housings. AES (Labtecta) isolators use an O-Ring in this location. This eliminates the problem of excess RTV plugging the drain ports and oil passages. I dislike the idea of a $1000 isolator sealed to the housing with RTV. This is not to inply that Inpro seals are not good seals, I just do not think they are the best option in our case.

This message has been edited. Last edited by: Big E,

We have had good experience with Inpro bearing isolators over many years. We have also used Protech isolators which is a cheaper alternative but does not always stand up to high temperatures (Non-metallic). We have had at least one Protech pop out with disaterous results. We have also started using Isomag seals but don't have much experience with them yet. I am not sure what is being refered to by double o-ring design. Some Inpros use double O-rings on the rotating element to shaft seal to keep the rotor stable (less likely to walk on the shaft). We have looked at Magtecta but have not yet tried them. We don't seem to have any compelling reason to switch from Inpro's other than price. We have recently installed an oil mist version of Inpro that we are hoping will reduce oil mist leakage to atmosphere. Isomags are good for this too but I'm not sure you get the same life or reusability as the Inpro.

Here is an article by Heinz Bloch that describes his particular concerns about an older single O-ring design. (See item 5)

http://www.machinerylubricatio...oil-mist-lubrication

As I read it, one of his concern is about using the O-ring as a means to fix the rotating seal assembly to the shaft, instead of rigidly clamping the seal to the shaft. Most of ours use an O ring to establish the position... shouldn’t be a problem because there is no force. I haven’t heard of problems with the rotating seal assemblies creeping on the shaft.

His other concern is that an O-ring can get shredded in the groove, which sounds similar to what Terry described. On first glance if there is possible relative axial movement between rotor and stator such as sleeve bearing motor, it seems like that could be a problem. For most other machines the positions don’t change and I wouldn’t think it would be a problem.

This message has been edited. Last edited by: electricpete,