Query Regarding Atlas Copco VSD Air Compressor GA37VSD

You raise an interesting question. At the moment I see little reason to "take sides" on any issues. It would be good to understand your load profile. Sustained running at 40% seems a bit low, as though maybe the compressor is oversized. However, if there are periods of running at nearly full capacity, that should not be much of a problem. Can you say further about how much the compressor runs for extended times at well less than full capacity?

Check their advertising against your use (they have minimum and maximum rates) and call them on it.

www.atlascopco.com.au%2FImages%2FBrochure_GA_VSD_English_tcm795-3536923.pdf

I think it should work with only 40% load. What gearbox are we talking about? It seems to be direct drive. And the VSD should regulate the speed.

If it doesn't say it in the manual, I would ask Atlas Copco what minimum output will avoid the problem. They have already implied this is higher than 40%, so I would try to arrange recommended minimum, with start/stop operation to give correct average output. Likely to need an air receiver, which must be sized to give acceptable start frequency. It might be possible to unload the compressor instead of stopping it, AC can advise.

I'm with Atlas Copco. You bought too much capacity and are running it too slowly.

See Codemaster comments.

Did an MBA within your organization participate in the system design or specification ? Was this unit purchased used ?

Did you change the gearbox lubrication regularly and in conformance with AC requirements ?

I suggest that you add another fairly large receiver (perhaps your first receiver) to the system. Receivers cost very little and can never harm the system.

Drop the set pressure where the compressor starts ( say to ~ 90 psig).

Have you calculated your ACTUAL system requirements ?

How does your ACTUAL requirement compare with your compressor capacity ?

Please try to answer these questions and not ignore them...

Why did you direct these question to me?

I Agree with you on this, Atlas Copco was one of my most expensive customers using AB PLC 5 systems at several racks per system. They know what they're doing. Worked with them for 20 years selling them all AB PLC5's and later on SLC500's plus VFD's and SMC's. Marty was their engineer I worked close with till 2005 when I had to get out and go back to building things, sales was not my thing. a 6 month job became a 20 year job and sent me to the loony bin. I am now where I belong.

But I Still stand with Lyn and Atlas on this issue. Customer ordered the wrong product for their needs.

Is there any means that you could find the temperature along the casing of the compressor and its discharge temperature and pressure.

If we could grasp to know it, easy to tell from steam tables, if condensation happens inside the compressor.

A simple solution is to install a large pressure tank on the discharge of the compressor- running at peak compressor pressure with an operating control to activate the compressor when the tank reaches system "design" pressure and install a PRV on the tank outlet to feed the system main at design pressure.

Size the tank based on the system demand (40% of peak output) for charging time of about 10 hours a day (40% of 24).

The compressor will operate at 100% capacity, then shut off with total power use that will be virtually the same as it is now- so no higher cost- while eliminating the problem you are facing.

Use the existing VFD (since it is there) to provide a ramp-up start to minimize wear on the gear train.

Agreed.

It makes sense that running slow at 40% load causes a sludge problem.

The compressor runs 'cold' and moisture condenses in the oil instead of passing through to the after-cooler.

But this does not explain why it causes the gears and element to fail unless it is due to 'cold' sludge blocking the oil feed pipes thus stopping the flow of oil; which on return to full speed causes excessive wear and tear until oil flows when the sludge 'melts' at working temperature. By which time the damage has been done - and when prolonged causes premature failure.

The whole point of a screw compressor is being able to run continuously at full load.