Gentlemen,

We have an SSR-125 IR Compressor that is kinda giving us fits. We monitor this thing monthly, in October '05 our trends started to become unstable and in February '06 the machine went in to alarm. Right off the bat we noticed a peak at 6480 cpm throughout the entire unit, motor speed is 1780. In March '06, 2x 6480 cpm increased from .04 in/sec to .49 in/sec. We were able to get motor bearing numbers, and fault frequencies do not match. We haven't been able to get any info on the compressor, but we believe there are 4 lobes on each screw. The amplitudes are the highest on the outboard motor bearing, the motor is overhung and flange mounted. We normally take our data between 100 and 109 psi, and have not seen much change in amplitude until now. On the 31st of March we had a sharp decline in amplitudes across the board. The compressor was only running at 93 psi, and we believe was and had been in an idle state. Also on the outboard female screw bearing we have 1/2x harmonics of 6480 cpm. Somethings got to be loose, right? We think this is all related to screw pass, but I want to be certain. Is there anything else that could be causing this???

IR_Compressor.doc (158 Kb, 27 downloads)

Steve,

Most Ingersol Rand SSR compressors have a gear set and a 4 lobe male rotor and 6 lobe female.

The data given to me by IR for 1 SSR125EP is as follows:

Motor speed: 1790 rpm
Drive gear: 48 tooth
Driven gear: 59 tooth
Ball bearing: 80BC03J30X
Thrust bearing: 80RU03T30X

The geartooth combination will vary among different units according to load demands and use. Some have a speed-up drive. You should be able to figure out how many teeth are on your gears by looking at about 80,000 to 150,000 cpm and finding the spike for gearmesh frequency. (It looks like you have something around 100,000 cpm with some sidebands that likely are spaced at motor or input shaft speeds.) The shaft speeds are probably 6480/6 and 6480/4 and 6480 is probably gas pulse frequency.

These should definitely been measured under a consistant load. If they cycle, make sure you are getting them while they are drawing air.

Specific information about your unit can be provided by Ingersol Rand in Davidson, NC. 704-251-1284. I also have a name of Art King and a number of 270-251-1284. I'm not sure who he is, but I assume from my notes that he has helped me in the past.

As far as your data, while the increase is of concern, I have seen these things run for years with much higher amplitudes. I would recommend that you begin to take PeakVue readings on all points and look for harmonics of shaft speeds and impacting in the waveform.

Good Luck,

Hello Steve,

The information Danny has provided is very useful and comes from the manufacturer. Being the numbers from IR correct, the lobes pass frequency should be very close to 5825 cpm assuming a 1790-rpm motor. This would mean that the harmonics of 6480 cpm do not come from the air unit but perhaps from bearings.
It is not clear if the bearing references provided by Danny belong to the air unit or the motor, but you can now find out that with IR. I think the 80BC03 is the same as a 6316.
Base on the information provided by IR, the speeds of your unit should be 5825/4=1456rpm for the male rotor and 5825/6=970 rpm for the female rotor. It would be good to check with IR if 6480/1456=4.45x and 6480/970=6.68x might be bearing frequencies for the bearings installed on male rotor/female rotor respectively.
On the other hand 6480 cpm at a running speed of motor near 1790 rpm is about 3.6x, which may be easily a bearing frequency.

The compressor surely is modulating the air depending on air demand, which means that load may vary a lot over time. While collecting the readings the compressor might even sometimes even run unloaded. You may start collecting your readings with the motor (compressor loaded) but by the time when you are in compressor tending end there is the chance that the plant needs not much air and the compressor runs without load.
To help with the consistency of your readings I would suggest putting the compressor to load in manual (not in automatic cycle) and vent air to atmosphere from the air mains while you collect the readings (simulating more load from the plant and assuring that the compressor does not run unloaded). It may sound as wasting energy but gives you the chance to have consistent readings.

Jorge,

As I mentioned, the geartooth combinations will vary from unit to unit and the ones that I referenced are for one particular unit. There can be a great deal of speed variation, so those calculations likely do not apply to this unit and are supplied only as an example. I strongly suspect that after checking with IR, Steve will find that 6480 is the gas pulse frequency.

I thought the bearings that I referenced were for the compressor, but since you questioned it, I'm not so sure. According to my the sales brochure, the thrust bearings are tapered roller and are located on the outboard end of the compressor and those numbers are for a ball and cylindrical roller bearing-more likely for the motor. My notes from the phone conversation 8 years ago are not very clear on the bearings.