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Jul 15 13 12:03 PM

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We have a compressor as listed above (air cooled version) and have had a problem that has crept up gradually over the last couple of months.
When switching to load the compressor does not respond and can take between 2 and 25 minutes to actually show pressure on the gauge.

Prior to switching to load there is zero pressure on the gauge .
We have performed checks on the solenoids and the pressure switch and the unit runs fine all day it's just start up.

Also it seems that the colder the temp the longer it takes to get pressure up.

I am an apprentice covering for the boss while he has an operation, we are trying to avoid having the Atlas Copco guys in for a look at this stage as they want $2000 before they even open their toolbox.(we are out in the stix)

Any advice appreciated.

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#1 [url]

Jul 16 13 9:38 AM

Hallo fitter,

in order for the compressor go in "load mode" the compressor needs to open the intake valve. So start from that point. Here is what you should do step by step:

1. Be prepared to follow the internal pressure - the pressure inside the compressor before the minimum check valve. Some of Atlas Copco compressors has a button which indicates the pressure inside the compressor on the main gauge, others have second gauge for the internal pressure - I dont know if your compressor has such option.

If not - install a gauge somewhere in the compressor before the minimum pressure valve and if possible after the separator filter.

2. Remove the suction (air) filter in order to get a better view on the intake valve. Take care to remove any objects from the "reach" of the intake valve in order to avoid falling objects in the airend.

3. Start the compressor and keep and eye on the internal pressure. In the beginning the intake valve should be closed and the air should use the bypass line for compressing. At that moment the internal pressure should be rising very slow. At a certain point the solenoid valve of the load line should open (could open immediately together with the delta - star switching).

4. If there is internal pressure and solenoid valve is open, but intake valve is closed, that means that the intake valve is not working.

Do the up mentioned procedure and let me know if the intake valve opens or not and what is the internal pressure.


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#2 [url]

Jul 17 13 3:11 AM

Thanks for the reply, I will run your check when I get the chance.

The compressor has just started to behave normally again but the morning temps have been higher so it will be interesting to see what happens when it gets cold again.

What could be the cause of no initial pressure at start up?

There is a gauge at the vent valve/ pressure switch area and a gauge at the front panel however they seem to run in unison.

The boss should be back soon so I may run all this by him as he has already checked part of the system.

Will keep you posted.

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#3 [url]

Jul 17 13 4:31 AM

The lack of initial pressure may be caused by a lot of reasons. The main reason is that the pressure delivery of the airend is smaller than the leaks. In this case you should check following things:

- Check if the unload (pressure relief) valve is closed
- Check if there are any additional leaks in the hoses (tubes) and connections in the compressor. In your case I think that there is a bad connection and when it is cold, there are higher leaks. When the temperature raises, the metal expand and the leaks stop.
- Also possible (although small probability) that the bypass intake line is stuck with some obstacles.

Best regards

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#4 [url]

Jul 11 14 4:17 PM

Your load solenoid can seem to be working but not opening fully or even be restricted by foreign objects. These particular inlet valves need air pressure to open, around 30-40 psi. If you are not getting a strong enough air signal threw the solenoid then the inlet valve will not open. This things are very finicky and could very well work then not work. I've been an air compressor mechanic for many years and have seen this happen many times.

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