Hello All,

I have just taken over a fossil plant that has an ash reclamation plant. The ash is moved by a series of Gardner Denver rotary lobe blowers. All of different sizes and models mostly sturobuilt 5MP, but there is also some 9CDL and 11CDL. I have been using the collections set up by the person who collected the data before me. I do not think that he has the right collection parameters set up for the se machines. I do not have a whole lot of experience with these types of blower. Could somone with some more experience shed some light on these for me?

All motor s are 1780
Blower speeds range from 1440-2160

I am not familiar with these particular machines so let me just offer general comments:
1. First, you state you dont think the collection parameters are set up right. Why do you say that?
2. Find out as much about the forcing frequencies as you can. I generally find that 0-10 orders (low freq) and 0-100 orders (hi freq) is a good start. Make sure the ranges cover all forcing frequencies and possibly several harmonics (e.g. gearmesh harmonics).
3. Make sure you are monitoring at all pertinents locations on the machine. Usually all the bearing locations.
4. What is repair history of these blowers? If they're failing more than you like, why? what is cause? Are you taking data often enough? Are your alarms appropriate? Are you taking advantage of all the capabilities (Demod, PeakVue, etc.) so the machine is giving up its secrets?
4. You can probably find more thread discussion on this topic elsewhere and in much more detail than Im providing here. If still confused, the software manuals should provide some guidance also. If need more info, contact me directly at ivibr8@yahoo.com with specific questions.

Regards
Jim P

The most common thing I see in these blowers is an increase in amplitude at 2 x running speed as material builds-up on the blower lobes. Impacting at 2 x per revolution will show in the twf. Many harmonics of running speed without 2 x being dominant usually means looseness in the bearing or shaft fits. Amplitudes normally run quite high, often higher than 30 g's p-p.

If this sounds elementary, please forgive me.
I'vev had good luck with Sutorbilts in the past, monitoring the following:

bearings- 25-30 orders of 1X

gears - VERY important. The gear counts are different for different sizes and applications. count them if you can.

multiples of 2x will be quite common. It's just the nature of the beast. Band around them if possible.

They will experience some build-up, but for the most part, are pretty tough machines. Clean oil, good alignment, proper gear timing and shimming, and proper lobe clearance are the biggies.

Again, if this sounds elementary, please accept my apologies.

Stan Riddle

Thanks for the input. I have been seeing running speed harmonics in multiples of 2 (2x,4x,6x...) all the way out to 12x I just figured that this was lobe pass but the amplitudes concern me (around .5-.6 ips on average). I know that generally the running speed amplitudes of these machines tend to run towards the higher range. I did read in the O&M manuals that high vibration could be caused by material build up.

Should I be putting more stock into acceleration and spike energy readings?

Keep the elementry stuff comming Stan.. it's all good stuff..

Like I said my knowledge of these blowers is very limited and I am just trying to make sure i am looking for the right things with my data.

We have similar (not same mfg) machines for our hull supply blowers in one of our Plants.
The running speed harmonics you measure (esp. 2X-B, 4X-B, 6X-B, etc.) are common and expected. No surprise.
The audible noise from these type blowers tend to be annoying to personnel stationed in the area. Data from a microphone taken at inlet muffler confirmed same lobe passing pulses as seen in seismic transducer.
However, looking at past data for both our blowers show these peaks are fairly consistent between 0.07 to 0.18 ips. So, your measured .5-.6 ips seems high to me.
Two questions:
- What is the trend on these blowers? Our blowers push clean air. So wondering if ash buildup has an effect on increasing these peaks?

- Does your system throttle the flow? Our discharge valves can be throttled if necessary and you may find this has big effect on lobe passing.

Regards
Jim P

Forgot to answer your question re: acceleration and spike energy.
I dont believe these will be of any help for this case. Your original post was not specific enough so just wanted to make sure you use all tools available to you.

Jim P

To answer your questions Jim:

It is possible that there is some ash build up. However the trend on the blowers inquestion has been up and down for abbout a year now. They do cycle so I try to collect the data under the same load conditions everytime although it's hard to time. The operators love to close the dicharge valve on these blowers to meet their needs and let the saftey open to relieve the excess pressure.(Unbelievable)

These blowers are run hard and are in a harsh enviroment.

I should have started out asking what to look for that was specific to these blowers?

But thanks for the info it is appreciated.

[QUOTE]Originally posted by jmul2380:

The operators love to close the dicharge valve on these blowers to meet their needs and let the saftey open to relieve the excess pressure.(Unbelievable)

Expect to see at least the 4X frequency increase when this is done.

You asked about accel and spike energy. From my experience, I collect the spectrum in accel out to 5 khz and use peak hold averaging. A loose bearing will be very obvious with this setup, which is our common failure mode.

Regards,

Mick,

Interesting. I have never used peak hold averaging. Can you post a sample spectrum?

Thanks,

I'll try.

PKHLD_NOV-10-2006.pdf (49 Kb, 53 downloads) Example of PK Hold vs. Normal Averaging

Mick,

You spectrum marker is at 3xSS with harmonics of that frequecy highlighted. Does the blower have 3-lobes on each rotor?

Walt

Yes, good observation.

Regards

quote:

Originally posted by Mick3040:
I collect the spectrum in accel out to 5 khz and use peak hold averaging. A loose bearing will be very obvious with this setup.

Mick,

I have few questions in regards to the vibration data you posted.

1.Why the diagnosis is a loose bearing? IMO, 3xRPM is caused rather by air pressure pulsations due to 3 lobes then loose bearing. At least I see this type all the time.

2. Regarding Fmax=5 kHZ.. With a dual pole magnet you may run into mounted resonance at such a high range. What extra information does such a high Fmax provide?

3. Regarding using Peak Hold averaging ... I have never used it before either. What is its advantage over normal averaging for velocity or acceleration data? Isn't PeakVue a better tool to see peak values?

Regards,
David

I like David's questions, but I didn't see where Mick indicated that he was using a 2-pole magnet. I always use a rare earth flat magnet, with a few exceptions. It would be good to discuss the merits of wide-band acceleration with Peak-hold rather than the abstract PeakVue. I have worked on several GD 2-lobe blowers in the 600-hp size at 700 to 900 rpm speed range. They had water injection for sealing. I am not sure how I could make a faulty bearing call compared to fouling deposits affecting light rotor rubs.

Walt

Those are really good questions!! Thanks for posting them.

5Khz Fmax. That was arbitrary. Hey all I knew was there was a recurring failure mode that our group was not catching. Easy place to start. Couple the higher fmax with acceleration units and a flat rare earth magnet and you saw the results.

I had a feeling that this might be an intermittent (non-periodic) issue. That's why the switch to Pk Hold. I didn't want to filter anything out with normal averaging.

When I was getting the data, I was floored at the difference between velocity/normal avg and the accel/pk hold data. The 3x harmonic pattern just lit up the spectrum!

Now to the 3x...

It is my opinion that as the looseness condition begins to advance, the clearances of the rotor lobes will change, causing an increase in vane rate without an increase in 1 x which is exactly what we saw.

So to finish, this is how our specific problem was addressed. I don't know if this will work for your situation, but hey, if you don't try looking at things in just a little different way, you'll never know which way to go next.

Regards,

quote:

Originally posted by Mick3040: A loose bearing will be very obvious with this setup, which is our common failure mode.

MICK,
Has a loose bearing been ever confirmed? If so, did looseness also manifest itself in vibration data in a "traditional" way?

David

Yes we did confirm a loose bearing on this pump and it did not show up in any other way.

Regards

Very useful and interesting discussion. Thanks. In our plant we are monitoring Lobe Blowers which functions as Vacuum Boosters. These Blowers are 'Tuthill' make. Other than Vibration monitoring, we monitor Lube Oil condition very closely as we have history of failure on one of these blower due to timing gear.

We use Acceleration Spectrum, Acceleration Waveform, Enveloped Spectrum apart from normal Velocity spectrum. But all with 'Linear' Averaging.

Do we need to use any other additional parameter?. I kindly request for your suggestion.

Thanks and Regards

Maha