Many industrial facilities depend on rotary screw compressors for their compressed air supply. Being efficient and reliable, it’s a design that’s well-suited to larger operations. As with any sophisticated machinery, regular maintenance is essential for consistent performance and long life. Here’s what you need to know about rotary screw compressor maintenance.
As Vital As Electricity
You can’t run a factory or processing plant without electricity. In most industrial operations, the same is true for compressed air. Manufacturers of every kind use it as an energy source, a transport medium and for processing.
Compressed air is essential for operating grippers, clamps and arms that grasp, hold and move product through machining, processing and assembly. It’s used as a transport medium in coating and painting operations; for conveying powder in chemical industries; and for cleaning, cooling and drying. Cut off the compressed air supply and none of those essentials can happen. That’s why fixing air compressor faults is always top of the maintenance department’s list of jobs.
The Importance of Compressor Maintenance
If the compressor goes down, it takes down everything relying on that supply. Actuators won’t move. Hand tools won’t work. There will be no air for cleaning, cooling, transport or any of the myriad other tasks it performs.
An air compressor breakdown in a large facility doesn’t stop just a single worker or machine. It halts an entire line and perhaps even the whole factory. Consequences can include missed delivery dates and overtime working to catch up to schedule. Plus, there’s the cost of making the repairs to consider, which likely includes charges for premium time. (When did a compressor ever fail in normal working hours?)
Even in a plant where the air system is supplied by multiple compressors, having one go down can disrupt production. Forced to ration air, management has to prioritize and stop less essential activities. A second possibility is that pressure drops sitewide. That can cause safety hazards as well as impacting productivity and quality. Third, the compressors remaining operational will spend more time running at full load.
Another aspect to consider is compressor life. As with any other machinery, regular maintenance extends life. That defers capital expenditure on new equipment, which mitigates depreciation charges.
Operating Principles for Rotary Screw Compressors
Before you can focus on fixing air compressor problems, it helps to understand the basic operating principles.
The heart of the rotary screw compressor is the pair of interlocking helical screws. These screws draw in air as they turn, gradually squeezing the air into an ever-smaller volume before it’s released into the compressed air system.
These compressors use an oil bath design where the screws run in oil. This seals the clearance between screws and housing, lubricates the motion, and removes the heat of compression. Compressed air passes through an oil separator that takes out the oil.
The helical screws form what’s called the “air-end” of the compressor. The other major component is the drive system. In some designs, this consists of a belt drive from a motor, others have the motor coupled directly to one of the screws.
Benefits of the rotary screw design include low noise, high efficiency and no pulsing in the compressed air delivery.
Advice for Rotary Screw Compressor Maintenance
The most obvious advice is to follow what the manufacturer recommends. Beyond that, points to consider can be grouped under the headings of the following:
- Operating Environment Impact
- Inspection and Cleaning
- Compressor Servicing
- Annual (or Less Frequent) Service
- Replacement Part Selection
Operating Environment Impact
The most common problems relate to blocked filters, contaminated or worn-out oil, and excess heat. The compressor operating environment plays a role in all of these and so should be considered when assessing the frequency of inspection and maintenance. For example, a compressor that runs in an air-conditioned room will benefit from cleaner air and a stable ambient temperature. Conversely, one used outdoors on a farm or in a mine will likely be exposed to dusty air and possibly also high ambient temperatures.
Inspection and Cleaning
It’s good practice to conduct a visual inspection once a day. This should include checking:
- Fluid levels
- Condensate traps
- For leaks
- For abnormal noise or vibration
In addition, clean exposed surfaces — particularly heat exchanger fins — on a weekly basis. This is an opportunity to detect any abnormal temperature rise and helps prevent overheating. It also makes any leaks easier to spot.
This entails shutting down the compressor. It’s usually done outside normal working hours. Many compressor manufacturers recommend servicing be performed on an hours-running basis. A typical number is every 2,000 hours. Although, this should be reduced for particularly hot or dirty environments. In operations where the compressor runs only one shift, servicing every three months is usually acceptable, again, adjusting for environment.
Points to address here are:
- Oil change
- Air and oil filter replacement or cleaning
- Check condition of drive belts or couplings, and replace as necessary
- Grease motor bearings
- Check pressure drop across oil-air separator and replace if above 10 psi
Annual (or Less Frequent) Service
Even with regular greasing, bearings will start to wear. Periodic replacement (perhaps every two or three years) will avoid the risk of failure. Further, it’s prudent to replace couplings or belts before any problems become apparent.
After many years of service, it may be worthwhile having a compressor rebuilt. With the tight clearances in a rotary screw compressor, it’s advisable that this be done by a specialist who can maintain the appropriate alignments and tolerances.
Replacement Part Selection
While generic or unbranded spares are available, it’s good policy to stick with replacement parts from the manufacturer.
There are two reasons for this:
- It’s usually required by the warranty.
- Parts made by or for the compressor manufacturer will conform to the original specifications for tolerances, hardness, etc. — and therefore will last as long as the originals.
Compressed Air Equipment From Kaishan Compressor USA, LLC
When processing or manufacturing operations depend on compressed air, you need proven equipment from a manufacturer you can trust. Kaishan has been making compressed air equipment for more than 60 years and understands what’s important to compressor users.
Our extensive product range goes from steam expanders and air receiver tanks to portable and fixed air compressors. Our family of rotary screw compressors includes belt drive, direct drive, single and multistage models. Contact us to learn more about Kaishan compressors.