With much fear and trembling, frustration and embarrassment, why have I gone through 3 Atomizing Air Compressors in less than 3 months?
Unit 7EA – Non DLN – Distillate – Water, Liquid Fuel, Atomizing Air Only.

What am I doing wrong?
What am I not seeing?
What have I not considered?

1. Physically all piping has been dismantled and checked for clogging – nothing there.

2. Borescope all piping and areas that can’t be physically seen – nothing there.

3. Valve V-18 – Borescoped in operation to check positioning – default position – open at all times – solenoid de-energized – everything ok.

4. Valve V-22 – Borescoped in operation to check positioning – closed position when energized solenoid – open position when de-energized solenoid – everything ok.

5. Check Valve – removed and inspected – ok.

6. Pre-Cooler Borescoped and Inspected – ok.

7. DCS Comparative Condition Studies – Blower, Atomizing Air Compressor, Turbine Compressor behavior – before failure to AA Comp – all seem normal.

 

You haven't described the failure mode of the compressor. How is it failing?

Those compressors spin at very high speed through an integral speed increase gear, driven by an output shaft of the Accessory Gear box.

Have you consulted with the compressor manufacturer? I have called Atlas-Copco several times with questions and requests for information and parts expediting and they have always been very helpful.

Alignment is probably the most important part. If the drive shaft is loose or not properly aligned that could be the cause. But, without understanding the failures it's really difficult to say.

Though you have already checked, the temperature of the air entering the compressor needs to be less than approximately 150 deg C (300 deg F). The setpoint of the atomizing air pre-cooler temperature regulating valve is supposed to be approximately 225 deg F and the reason for that is that the air entering the compressor needs to be hot enough to prevent moisture condensation. If the air temperature is too low moisture will condense in the cooler shell and can eventually be pushed along into the compressor where it will cause damage. There are shell drains which can be monitored during operation to check for condensate.

If you are using a Robertshaw temperature regulating valve it is very common for High AA Temperature alarms to be annunciated during start-up, and for people to misadjust the temperature regulating valve to try to prevent the alarms. If you think about the valve setpoint and the valve position when the unit is shut down, it's trying to stop the flow of cooling water to make the ambient temperature equal to 225 deg F. Then when the unit starts, because the valve is slow to respond and open the alarm will be annunciated for a brief period of time (a few minutes) until the valve can open to begin lowering the AA temperature.

Lastly, adjusting the Robertshaw temperature regulating valve is a mystery to many people. the handle on the side of the valve is NOT the automatic adjustment; it is a manual over-ride of the automatic adjustment. There is a small triangular-shaped adjusting "wheel" underneath the bellows that is the automatic adjustment. The handle on the side of the valve needs to be put into the AUTO position (so that it does not affect automatic stroke). Then the triangular "wheel" needs to be turned to make the adjustment.

Adjustment needs to be done when the unit is running at a stable load. Adjustments to the "wheel" need to make slowly, 1/3 or 2/3 of a turn at a time, and then you need to WAIT for the AA temperature to stabilize after the adjustment; sometimes it takes 10 or 15 minutes.

The Robertshaw manual, if not in the GT service manuals provided with the unit, is available for free on the Robertshaw web site. There is some information in the manual about the adjusting mechanism.

The capillary tube of the temperature sensing bulb can be, and is quite often, easily damaged by uncaring mechanics and pipe-fitters.

Check with the compressor manufacturer, and do a very good visual inspection of the Acc. Gear drive shaft and bearings and shaft/splines. Ensure the temperature regulating valve is working properly. Check the shell drains for condensate periodically.

And write back to let us know what you find.

 

you might describe the details of what has failed and what you have monitored, such as pressures, temperatures, etc

 

You give us a lot of information but you omit to tell us what temperature you were running your AA at? Too high can cause one failure, too low another.

Can you tell us what kind of failure you are getting?
Is this a new machine or have these failures suddenly started on a machine that has been running for a long time and was OK?
If it is the latter, was anything done to the machine that may have caused the AA comp.failures (maintenance,changes,etc.)

 

hi john

i am interested to add some more check list points...
we faced the same problem with our two frame v machines and we changed AAC three times.

pl.do these things also

1)check the lube oil quality.if it has impurities like metal parts or any rubber material,change the lube oil fully and also check from where they came.

2)check the lube oil filter change over valve,in this valve one rubber pad is present to close the lube oil entry in reserve filter.it may be damaged due to aging.

 

Hello,

If its a failure of impeller then its a known problem with Atlas Copco.
There is a TIL which describe what to do in that case.

Also what is the atomizing air temperature after atomizing air cooler? This temperature should be more than its dew point. Generally above 100 and less than 110.

Also there is a bleed point just before NV-101 (before compressor suction) to drain out any water that might have condensed. You might want to check that for blockage.

 

Umar,

Do you have the TIL number, please?