Maintaining Your Rotary Screw Compressor

By In Tips On February 19, 2016

Whether you work in a mine or another industrial sector, rotary screw compressors are an important part of your daily routine. Compressed air has become the fourth utility. Compressed air is just as crucial to production, in most cases, as electricity, gas, and water. If you regularly use a rotary screw air compressor you know how important it is to properly maintain your compressor. But often it is easily neglected, until it stops working. It is crucial for your compressors to be properly maintained for your equipment to be reliable and efficient, to maintain profitable production.

Despite their complex design, a rotary screw compressor’s basic function is simple. When two screws turn, air enters into a chamber. As the screws turn the area in the chamber gets smaller which causes a decrease in volume and a rise in pressure. Mechanical or digital controls are set to allow the compressor to operate within the desired pressure ranges.

Although the basic function is simple, many different complex parts work together for a rotary screw air compressor to operate correctly. Thus, like any other mechanical equipment, such as a car or a lawnmower, your rotary screw compressor requires regular maintenance.

Due to the complex nature of the compressor, safety, oil types, and the importance of reliable and efficient operation it is highly recommended you consult a trained and competent person before doing any maintenance to this type of equipment.

Safety First!

As with all equipment, proper personal protective gear and training prior to operating, adjusting or maintaining a compressor is a requirement. Be aware of safety risks. Always lock and tag out the electrical supply as well as the isolation valve on the compressed air piping. Be sure to verify that the power is off with a trusted meter, and vent all air pressure prior to performing maintenance. Be aware of hot surfaces, pinch points, rotating parts, hot pressurized oil, and high air pressure.


Just like a car needs regular oil changes, to maintain lubrication between its moving internal parts, your rotary screw compressor requires periodic lubricant changes. Oil in a rotary screw compressor is also used to cool, clean, and seal. Which means the compressor oil is that much more crucial to the compressor’s operation. If you fail to change the lubricant, it will become dirty, lose its lubricity, become contaminated with acid or even varnish and clog the oil filter. Without the correct type and viscosity of clean oil, the rotors and bearings will not be cooled and lubricated properly. Inevitably neglect will cause internal damage to the compressor which will shorten its life and cause it to fail.

Check the owner’s manual to determine how often you should change the lubricant in your compressor model. Also check the owner’s manual to determine which lubricant you should use.  Special screw compressor lubricants are designed to handle the high heat loads generated during compression. Also compressor oil is designed to protect from corrosion. The manufacturer supplies the lubricant with a recommended amount of hours the oil can be used. Some oils are recommended to be used for 4000 hours, while others for 8000 hours. The manufacturers’ recommendation is only a recommendation. Certain environmental aspects in your compressor room or your plant can affect the oil’s life span. It is critical that you regularly send oil samples to the manufacturer to avoid contamination and costly repairs.

Any residual oil left over in the machine will contaminate the new oil and lead to early lubrication failure. It is critical to get all of the old oil out of the compressor, which can be a very complex process. Oil will stay in the airend, cooler, and piping. Since changing the lubricant and knowing which type of oil best suits your specific application can be a complicated process, it is best to consult a trained and competent air compressor technician.


Your rotary screw compressor has an oil filter, an air inlet filter, and an air/oil separator. Like changing the oil, changing the filters will prevent your compressor’s parts from failing prematurely and prevent the oil from becoming contaminated. You should replace both the air filters and oil filters every 2000 hours of use at a minimum. In dirty environments the filters may need to be changed more often. Separators are typically manufactured to be used for 8000 hours. But there are some machines that require the separator to be changed more frequently.


The screw element of your compressor, also known as the airend or pump, is the heart of  your compressor. While airends can last well over 40,000 hours, they might still incur damage before they reach that point. Overheating, improper lubrication, condensation, corrosion, over pressure, incorrect control adjustment, and vibration can all lead to premature failure. Check for oil seal leaks and bearing noise.  Call a compressor technician if you suspect pending failure.

Drive Train Parts

Rotary screw compressors can be either direct coupled or belt driven.  Belt driven machines require the belts and sheaves be checked every 500 hours.  Direct drive machines need to be aligned if the motor is not flanged to the airend. Alignment is crucial and will undoubtedly cause early bearing failure in the motor, airend, or both. It is best to have a technician verify that your machine is aligned properly before running, and any time after you relocate your compressor to a new area.

Motor Bearings

The motor bearings require periodic lubrication.  Lubricants keep the bearings cool and prevent them from thermal breakdown and premature failure. Types of motor grease and the amount of grease used is crucial in an electric motor. Over greasing motor bearings will cause premature failure. Mixing grease types will also cause bearing failure. Consult the manual or your distributor for the correct type and amount of grease to be used.


Inspect and adjust controls, gauges, drains, indicators, and safety shutdown switches for proper and safe operation monthly. Keeping the compressor clean makes maintenance easier and safer to perform.

Avoid Overheating

Your compressor can reach very high temperatures in hot environments. Rotary screw compressed air discharge temperatures are usually about 100 degrees Fahrenheit above room temperature in normal conditions. If they’re placed in a hot room, they could overheat and shutdown. Overheating also will cause premature oil failure. It is important to make sure your oil temperatures and discharge temperatures are not excessive.

Coolers need to be clean for the compressor to run at the proper temperature. If it does overheat, check for common problems. For example, low oil level, the cooler might be blocked, or your ambient temperature maybe too high. Ask a service technician for help before you develop an expensive issue.

If you have any questions regarding your compressor or any other compressed air equipment consult a professional.

Mention this post when calling Compressor Pump and Service to receive a discount on your next service call!

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