How to stop and start air and water-cooled compressors, dryers, and gas generators

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If you’re wondering how to stop a compressor due to low production volumes, the following rules should be applied:

• General recommendation: If production is stopped completely, manually stop the compressor, even if they are integrated to a central controller. If this is not done, it’s possible that the machine will run at minimal capacity to compensate for small leaks in your compressed air network. This may be harmful (for example, it will create condensation in Atlas Copco GA machines).

• VSD compressors: Carry out a program stop, and make sure the electrical power supply is left turned on to keep the capacitor bank charged and ready for the restart.

• Water-cooled air compressors: After stopping the water-cooled air compressors, be sure to isolate the water supply. This will stop condensation from forming inside the water-cooled air compressors’ element(s).  Don’t forget to turn the water-cooled air compressors back on at start up. Please make sure any air blast cooling systems are turned off before turning on your water-cooled air compressors.

• Atlas Copco Z compressors: These need the main drive shaft to be manually rotated via the motor drive coupling, 3 complete rotations, once a week during the starting and stopping procedure of the air compressor. This is to prevent the low-pressure and high-pressure compression stages from seizing up during a long period of downtime. If the Z Compressor is a VSD version, don’t forget to turn the power supply back on after turning the compressor over by hand, to protect the inverter drive capacitors.

• Centrifugal / ZH compressors – The centrifugal compressor should be programmed to stop, and leave the power supply on.  When considering how to start the compressor, it needs to have the auxiliary oil pump turned on once a week for 10 minutes whilst the compressor is stopped. This will maintain the oil temperature and periodically start up the auxiliary oil pump to circulate warm oil around the bearings during long periods of downtime.

• Dryers (adsorption or refrigerant) and gas generators can be stopped manually and depressurized if required. For gas generators, when depressurizing you should monitor the oxygen level in the machine room.

Now that you know how to effectively stop a compressor, it’s also crucial to learn how to start a compressor. Remember that before turning the equipment back into operation to complete the starting and stopping procedure of the air compressor, a visual inspection is needed. So, how to start a compressor efficiently?

Begin the procedure by first turning off the power supply to the air compressor, removing the drive shaft protection guard and turning the drive coupling to check that the compressor is free to turn. If the compressor turns freely, re-fit the guard and turn on the power supply to the compressor; turn on the cooling water if you’re using water-cooled air compressors. Slowly open the compressor air discharge valve until the air pressure equalizes between the compressor and the air net. Start the compressor. The compressor is now back online. If the air compressor is connected to a sequence controller, make sure the compressors are integrated onto the controller/ optimizer.

How to start compressors for adsorption dryers and gas generators? Never start up against an empty air net. When starting, close the outlet valve behind the dryer or generator and pressurize the system. Then slowly open the outlet valve to pressurize the air-net, this to avoid high air speeds damaging the adsorption material.