Off Topic Post on compressors. Please Read.

[AndEdtec]

I'm sorry to bother you all with this post as it is off topic but Im sure somebody here could help me. I do use PLC'S and have found this site very helpful.

We have some compressors onsite , 45, 37, 11, 50 KW.. I use outside companys to service them and breakdowns but started doing some of the things myself.

But I have come accross a problem that I can't get my head around is there any resoures for understanding rotary screw compressors out there?

 

[rsdoran]

I am not sure what issues you may have but I will offer some things. Rotary screws look like this:

The mated surfaces allow a more constant pressure output with the ability to vary motor speed for savings on power usage. This article may help explain some of the differences between reciprocation and rotary screw usage:
http://www.compressorservices.com/html/whichone.html

http://www.irtools.com/IS/category.asp-en-3186

I may have more in-depth information that I am not finding right now. If you can state what specific issues you do not understand then maybe more can be offered. If possible state brand and model of the units you have.

 

[silva.foxx]

Probably the best place to ask is http://www.refrigeration-engineer.com as many there deal with screw compressors.

http://www.domnickh.co.uk/tech_Centre.asp?chapter=1&section=3_Screw-Compressors_2_3.htm&getIndex=false

 

[AndEdtec]

Thanks, I have a good understanding on how they work but I have a problem with an atlas copco GA510.

The compressor runs and makes air, so the suction box is open allowing air into the screw. Air filter is good. Seperator is good oil filter is good.

The problem is than when the compressor is unloaded the temp builds up and cuts out on over temp. When the compressor is loaded it seems ok and holds its temp.

So I think the oil is not going through the cooler? But why?
Is there a bypass valve?

A friend said it sounds like low sump pressure! But I haven't got the knowledge on compressors to fix it. Please help me find the info I need.

 

[Maj. Toxido]

Thanks, I have a good understanding on how they work but I have a problem with an atlas copco GA510.

The compressor runs and makes air, so the suction box is open allowing air into the screw. Air filter is good. Seperator is good oil filter is good.

The problem is than when the compressor is unloaded the temp builds up and cuts out on over temp. When the compressor is loaded it seems ok and holds its temp.

So I think the oil is not going through the cooler? But why?
Is there a bypass valve?

A friend said it sounds like low sump pressure! But I haven't got the knowledge on compressors to fix it. Please help me find the info I need.

Try to check the following

1. Oil Quantity - Top up oil if needed
2. Cooling Unit Soiled - Clean cooling unit externally
3. Insufficient cooling air quantity - Keep air inlet opening to
the compressor clean;check to ensure that any existing cooling
air duck system are adequatly dimensioned.
4. Ambient temperature too high - Employ suitable measures to
improve the air inlet & ventillation in the installation room.
5. Temperature sensor defective or wire break - Replace
temperature sensor or repair the wire break.
6. Check also the air end & solenoid valve in loading &
unloading the air,cause it trigger the high temperature alarm.

Regards:

Sherwin

 

[AndEdtec]

Hello, I have checked all the obvious things and my understanding is begining to get better.
The areas I need to improve my understanding are on the sump pressures of compressors.

I now understand some compressors have a Zero Sump pressure or a positive pressure.

I understand screw compressors still need some oil passing through the screw when on unload.

The pressure in the oil vessel/sump should be around 30 psi.

I can now check this.

Also if the compressor isn't unloading properly.

Also the screw could be damaged.

Where can I find more info to help me understand more?

 

[Tom Jenkins]

These sites may have some additional info for you.

http://www.gardnerdenver.com/blowers/NewBlowers/index.html

http://www.rootsblower.com/

The discharge pressure of a positive displacement blower tends to rise as the discharge pressure increases or as the speed decreases. If this is not a constant speed blower you should check to make sure they don't go to a very low speed before the blower unloading valve opens.

Another possibility is that the unloading valve is being dumped back to the compressor inlet and not to ambient. If that happens the discharge air and blower temperature will increase because the waste heat just keeps going back through the blower.

You don't clearly state if the "high temperature" is based on discharge air or blower case temperature or just on an oil temperature sensor. Most blowers will have both types of sensors.

It is unlikely that the lube is being shut off when the unloading valve opens. Most systems like this have the pump on whenever the blower is on, either by a pump geared off the main blower shaft or an electric pump with interlocks that must run whenever the blower is on.

Usually there are also several lube temp sensors, ahead of and after the heat exchanger, in the sump, and exiting the blower. Which one is tripping?

 

[plchacker]

If the oil is air cooled, check to make sure the heat exchanger is clean. Cleaning these is a dirty job. They are often neglected. Because things start to heat up in unload, slight cloging of the fins can cause your trouble. You mentioned that the oil filter is good, what about the oil?

There is no bypass that I am aware of. But oil can circulate whether air can or not. Make sure air can circulate. Nasty, nasty job, but well worth the effort.

 

[vufu]

May be I'm wrong, but couple years ago I had similar problem with Atlas Copco compressor, our loading solenoid valve was broken.

Vufu

 

[AndEdtec]

Sorted my problem now, was a combination of not enough use and possibly a dodgy new oil filter.

However I do understand them better now. Thanks for all your suggestions. Below are links to 3 very good websites for rotary screw compressors.

http://www.airengineering.com/techhelp.htm
http://www.airends.com
http://www.airengineering.com/techhelp.htm

However I would still like more info if anybody has got any, Servicing guides or manuals for any compressor.

 

[Maj. Toxido]

However I would still like more info if anybody has got any, Servicing guides or manuals for any compressor.

Try BOGE, Kaiser, & Ingersol Rand Compressor.
I maintain & troubleshoot this type of compressor in the plant.


Regards:

Sherwin