Compressor Operation Below Dictated RPM

(a) No.

(b) Yes. Reduced lubrication. How are they lubricated? I'm not going to research this further.

(c) Clients engineer.

Sparkys should stick to OHMS.

Atlas Copco Air Compressor Problem Talk to this guy. Maybe you can trade notes.

Lyn dear,

Please give me more details. Also operating at 900 rpm instead 3730 rpm did it save electricity? Why was it 3730 rpm in the first place when the engineer thought that by setting the pressure at 7.5 bar the VSD works to maintain at 900 rpm.

That would be a question for your electrical engineer.

Normal motor speed is 3450 at 60Hz and 2850 at 50 Hz.

3,730 RPM doesn't sound normal, but I'm not a sparky.

Why would anybody in their right mind run a 3,450 motor at 900 RPM.

If your EE said this is OK, fire him!!!!!!!!!!!!!!!!!!!!

I would think 3,730 RPM is the compressor speed, not the motor.

I can't see why operating at lower pressure would hurt it, other than that I agree with your #1.

Sorry, my mind is literal. Compressor speed = motor speed.

False economy all around.

A gear box in between, perhaps...

We may never know.

I was operating the compressor on 25 to 35% and after 2 years i am increasing it up to 80%. it might be the problem or not for damaged it screw.??

NOT the manufacturer

The client's Engineer for operating it outside the manufacturer's envelope, in the same way as the car manufacturer is not liable for the crash if the driver aims it at a brick wall.

a) What does the operating manual say?

b) possible but it will be laid out in the operating manual

c) usually the user is at fault. (this is your client? -Ups)

If the second compressor is identical and running with these parameters with no problems it sounds like oil contamination, incorrect oil or poor assembly may be playing a part. As your guy is an engineer I am sure he/she read the manual and ensured the parameters set were within scope. The manufacturer repaired the first failure so I would think the settings entered are correct, if not they have failed you in the customer backup and service department and shouldn't have let you start it up again using incorrect settings that may damage your equipment.

Hello Grochy,

Yes the 2nd Compressor is identical and running with these parameters.

When the manufacturer's service personnel for #1 compressor told the engineer to run at 3730 rpm instead 3730 rpm and when the rpm was increased the screw gear damaged (similar to situation as Lyle sent of Zubair Khalil's as:

"Atlas Copco Compressor Problem"

11/27/2014

I am using Atlas Copco compressor 37 VSD Ff (3600 rpm) last 04 years. but now our need we increase the load on that compressor its screw gear damaged. Is this happening by increasing in load...?or there is any other issue to be considered regarding this problem.

So #2 same model running at 7.5 bar & 900 rpm - no issue. Now if he increases this to 3630 rpm & 12.8 bar(put a PRV set at 7.5 bar) will there be same result of screw gear damage?

a. Yes it is OK to set this compressor at 7.5 barG.

b. By setting the pressure the compressor should adjust the speed to maitain a constant 7.5 barG. (The internal minimum pressure valve will be set at about 5 barG and will maintain enough pressure to keep the oil circulating.) If the demand is too low the compressor will unload and possibly stop. If your engineer has set the inverter at a fixed speed then this may be a mistake, this will be at or even below normal minimum speed. Sounds like the compressors are too big, running slowly is not efficient for this type of machine

c. How long hs it been running for? Air ends do wear out andneed to be overhauled. 30,000 to 40,000 hours is all you can expect between bearing changes

Manufacturer must have provided data on permissible working conditions. If 900 rpm combined with YOUR working pressure is within suggested range, then it is a problem with the manufacturer, equipment maintenance etc. In a machine designed from ground up to work with VSD, low rpm shouldn't be the failure reason, but manufacturer has the last word, at what conditions he has tested and can guaranty his equipment to work. The main thing is that in most cases, cooling systems performance rapidly deteriorates on low speeds. On the other hand, lubrication for a machine designed to work at variable speeds shouldn't be a problem for a serious manufacturer like Atlas Copco. S.M.

Whatever might be the reason for failure, and whether you can run at lower than rated speed, is something Atlas Copco can tell you.

But in your in search for answers, bear in mind the critical importance of the oil injection aspect, because oil is not just a lubricant, but also a sealant in the air-gaps in the screw to prevent air blowing back under pressure - that gets worse at higher pressures. Hot air gets re-crompressed to even higher temperatures - the oil thins more, and backward leakage worsens. There comes a time (soon) when a max pressure is reached.

Running hot, the oil breaks down and coats the oil/air separator element with 'varnish'. The filter blocks and could collapse under pressure. The oil gets dumped in the pipework and machines.

Runing slower avoids this sort of problem. But may cause a loss of oil flow where the lubrication aspect itself could become critical. Have you been using 'cheap' oil?

But this is all basic stuff, and Atlas Copco should be able to answer all your questions.

"But in your in search for answers, bear in mind the critical importance of the oil injection aspect, because oil is not just a lubricant, but also a sealant in the air-gaps in the screw to prevent air blowing back under pressure - that gets worse at higher pressures. Hot air gets re-crompressed to even higher temperatures - the oil thins more, and backward leakage worsens. There comes a time (soon) when a max pressure is reached."

..Lets not forget that wonderful 'diesel' cycle Mr. Gustav realized.Though I'm pretty sure he didn't intend for air compressors to experience combustion.

HTH

J

The oil also helps remove all that pesky heat of compression, too.

Yes you are right. 'Dieseling' is a common occurrence with compressors. Compressors catch fire.