Squealing Mycom V shaft seal

[PaulZ]

The issue had been posted by Ranger1 a while ago but there was no possible cause posted.
We have a Mycom 250 VSD that was rebuilt and had a new Mycom bellows seal installed.
When the compressor was run up there was a squealing sound coming from the seal area. The alignment has been checked and I asked the mechanic onsite to check the soft foot on the compressor which he did and found to was out a fair bit. He shimmed the compressor and ran it and the squealing got worse.
We have replaced the bellows seal with a BOS seal as was suggested by one of the posters.
We have install many bellows seals in Mycom V series machines with no problems in the past.
I would be nice to know the cause as replacing with the BOS seal solves the noise but doesn't tell us what the cause was.
Regards
Paul

[RANGER1]

Paul,
I don’t think anyone knows exactly.
Mycom Australia will say do not fit bellows to a machine that was not originally fitted.
If a "V" more than likely had one from new


Hopefully seal "0" ring & gasket installed correctly for lubrication.

[PaulZ]

Thanks Ranger someone may be able to suggest a cause. As far as we are aware it had a bellows seal from new.
Regards
Paul

[RANGER1]

Paul,
Have you referred it to Mycom for their comments?
What conditions does compressor run, refrigerant etc.
Have you Luke at MSE, he is aware of our industry issues on this matter.

[PaulZ]

Hi Ranger
Thanks for the reply.
The issue has been referred to Mycom and they have advised it was common with this model compressor apparently harmonics in the bellows.
They suggested changing to a BOS seal which we have done, they also suggested changing the cover plate.
They said the other option was to go back to the old Teflon Ring seal, they still have but very expensive.
No guarantees with any of the options.
The squealing has stopped apparently.
Compressor is running on a coldstore low stage I believe.
Who is Luke and MSE not familiar with either.
Regards
Paul

[RANGER1]

Hi Ranger
Thanks for the reply.
The issue has been referred to Mycom and they have advised it was common with this model compressor apparently harmonics in the bellows.
They suggested changing to a BOS seal which we have done, they also suggested changing the cover plate.
They said the other option was to go back to the old Teflon Ring seal, they still have but very expensive.
No guarantees with any of the options.
The squealing has stopped apparently.
Compressor is running on a coldstore low stage I believe.
Who is Luke and MSE not familiar with either.
Regards
Paul

Paul,
Can you explain cover plate, what they mean?
Is it seal cover?

[PaulZ]

Hi Ranger
Yes it's the seal cover.
Regards
Paul

[RANGER1]

Hi Ranger
Yes it's the seal cover.
Regards
Paul

I wonder why?

Out of interest, is this low side machine set for booster clearance, or standard?

[PaulZ]

Hi Ranger
My only thought about the seal cover is the seat material is a different to a standard seal cover. I have experienced seal problems if the wrong grade of carbon is used.
Mycom could not give any definite reasons as all their options were "this might help but no guarantee it will stop the squealing".
I hear from the mechanic today and the seal has stopped squealing with the BOS seal fitted.
I can't answer you question regarding the clearance.
I always like to know why a problem occurred by changing to a BOS seal it stopped the noise but I still don't know why the seal was noisy in the first place.
Regards
Paul

[RANGER1]

Paul,
Another tip, which not convinced entirely , is fill seal chamber with oil before start.
Manual does mention it, but we usually have oil pump start first.
Worth a try, just another procedure in our day.

[Tycho]

The only compressors I have seen a bellow seal on is the Howden XRV 127, but I have never heard any squealing.
Might have to do with the compressor itself being in the high end of the noise spectrum (the geared ones)

I do remember a conversation I had with one of the old hands some 20 years ago.

We were on a rush job and we got a non OEM shaft seal delivered, and it was a bellow seal one.

The old hand said a lot of things I shouldn't say here, and then "ok, we'll have to fit it to get them back in production"

While I was the wide eyed tool holder, he kept grumbling about the bellow seal and in my education he asked me "can you tell me why a bellow seal is not a good idea on a horizontal shaft on a compressor?"
I didn't have an answer
he came back with "yeah, too soon for you... anyway, bellow seals allow for gas to gather inside during standstill, so they will start with a "dryspot" on top, also during running, as the seal is rotating it will generate a little bit of heat, and that dryspot we had during startup will constantly be there as refrigerant boils out of the oil while the shaft is running"

Then he continued that bellow seals were only good for seawater pumps and piston compressors.

That's my extent of knowledge on the bellow seals :)

[PaulZ]

Hi Tycho
Most of the Howden comps I have worked on had Crane 109B seals with a carbon seat, O ring and teflon wedge. There could be something in not using bellows seals in screws.
The logic of the old hand is probably correct when you think about it.
Regards
Paul

[RANGER1]

Sorry to say but nearly everyone uses bellows seal.
A handful squeal & we get upset.
Mycom used the “BOS “ single seal with lots of “0” rings.
If seal had been in service for awhile, all good.
Depressurise machine to do oil filters of work, “0” rings disturbed, most cases then had to replace “0” rings or seal, that can upset your day.
Bellows proven reliable seal, better than any other seal for simplicity etc.
can say bellows quality has probably dropped off since China got involved, or design engineers reduced quality as they last to long.
Howden seal were crap & we use welded metal bellows seal, no more problems.
I would also suggest carbon faces, or whatever they are now is contributing.
WMB used in Mycom, Grasso recip, Bitzer, Howden, Sabroe, Frick large machines.
Like I mentioned prime seal chamber, as Sabroe S80 series also suggest this like Mycom.
Seal starts with chamber full of oil, fully libricated.

[RANGER1]

The only compressors I have seen a bellow seal on is the Howden XRV 127, but I have never heard any squealing.
Might have to do with the compressor itself being in the high end of the noise spectrum (the geared ones)

I do remember a conversation I had with one of the old hands some 20 years ago.

We were on a rush job and we got a non OEM shaft seal delivered, and it was a bellow seal one.

The old hand said a lot of things I shouldn't say here, and then "ok, we'll have to fit it to get them back in production"

While I was the wide eyed tool holder, he kept grumbling about the bellow seal and in my education he asked me "can you tell me why a bellow seal is not a good idea on a horizontal shaft on a compressor?"
I didn't have an answer
he came back with "yeah, too soon for you... anyway, bellow seals allow for gas to gather inside during standstill, so they will start with a "dryspot" on top, also during running, as the seal is rotating it will generate a little bit of heat, and that dryspot we had during startup will constantly be there as refrigerant boils out of the oil while the shaft is running"

Then he continued that bellow seals were only good for seawater pumps and piston compressors.

That's my extent of knowledge on the bellow seals :)

Tycho,
Can’t see the difference with WMB to standard seal, regarding dry spot.
Other seal types in same scenario the way I see it.
Howden do not have a seal chamber like a lot of other screw compressors.
The have a labyrinth seal which oil can run out on standstill.
Most machines now have a lip seal or similar to hold oil in chamber for extended periods.

[RANGER1]

Tycho,
Out of interest this is type of seal we are talking about, welded metal bellows.




https://www.flexaseal.com/products/mechanical_seals/component/compressors/mycom-200/

[Tycho]

Tycho,
Out of interest this is type of seal we are talking about, welded metal bellows.




https://www.flexaseal.com/products/mechanical_seals/component/compressors/mycom-200/

I don't have any issues with bellow seals, it was just a random thought that popped into my head when I read the original post.

:)

[RANGER1]

I don't have any issues with bellow seals, it was just a random thought that popped into my head when I read the original post.

:)

No worries Tycho.
JUst thought I would show picture as there is also a rubber bellows type seal which would be more common in water pumps etc.