Low amp draw

[mjpetrag]

This problem has been a bit baffling so I will try to include everything we've done with troubleshooting...

It's an IR x-flo centrifugal one stage air compressor that normally runs at around 90 Amps @ 15 psig discharge and 1.9 MMSCFH.

Currently it is running at 65 Amps @ 10 psig discharge and 1.9 MMSCFH.

We checked the suction filters, replaced all of them, and ruled them out.

We then removed the suction spool, cycled the inlet guide vanes, marked on the positioner 100% open and 0% open. The vanes cycled fine.

We then removed the discharge check valve, found that it had two broken springs, but realized it wouldn't cause the low amp draw we were seeing. This check valve was replaced. After that, the compressor was started. It did the same thing, 65 amps @ 10 psig discharge and 1.9 MMSCFH.

The inlet guide vanes are opened at 100% as marked by when they were cycled without the suction spool installed.

The speed of the motor is right on as it's always been.

Vibration at all 16 sampling points are all in normal operating limits.

I did notice one thing that was strange. There are 4 pressure sampling points, 2 are local and 2 go to our DCS. There are 2 gauges on the discharge before the duo wafer check valve that broke reading 10 psig. There are 2 after that check valve. One reads around 5 psig, and the other reads 10 psig. The one reading 5 psig is what the compressor uses as it system pressure feedback to either open or close the inlet guide vanes. It may be reading a false low and closing the inlet guide vanes to match system pressure, however the inlet guide vanes are open 100% by the valve positioner and the electronic indicator on the control panel. That is the only inconsistency I have been seeing.

Anyone have any other ideas what to check for?

-Mike

 

[zdas04]

So you've got a compressor that draws 90 A at 15 psig (lets call it 29.5 or 2.03 compression ratios) discharge. Now it is drawing 65 A (28% less) with a 10 psig (call it 24.5 psia or 1.69 compression ratios) discharge. My recollection is that current draw is a function of compressor hp and compressor hp is a function of compression ratios. I would expect that lowering the compression ratios 17% would account for much of your reduced current draw.

You didn't say why the discharge pressure dropped.

David

 

[mjpetrag]

We are trying to find why it can't build pressure and get the amp draw it used to have.

-Mike

 

[pmover]

what was changed?

before 90-amp draw & had suitable pressure, something was changed, now 60-amp draw and less pressure.

if nothing was changed exterior of the unit, then perhaps something is wrong with the compressor.

hope this helps.
-pmover

 

[Pumpsonly]

This may sounds insulting. How about the rotation?

 

[mjpetrag]

Rotation is OK.

More investigation from IR found a few things wrong with the controls to the inlet guide vanes (apparently the control scheme for the mode it was running in is antiquated and only a handful of people know how it works). There could be a problem with the GE Multilin limiting power to the motor according to our electrical engineer. It looks like the amps flatline at ~65 and can't get higher.

The mechanical side of things is looking OK except yesterday we found the labyrinth seal on the thrust bearing leaking oil. Looks unrelated to our amp problem however.

-Mike

 

[dcasto]

a compressor doesn't build pressure, it only creates enough pressure to meet the demand.

 

[Fzob]

Have you checked the flow meter? As pointed out the compressor meets demand. If for some reason the flow meter was off it could account for the difference you see in perfomance.

 

[CaracasEC]

Based on the performance curve of a centrifugal compressor, a compressor will have its head go down at the same time the compressor power go down if it is on choke flow condition. Could you check your gas velocity?