They are used to power the operations of a wide range of businesses, from industrial plants to major tire repair centers, to mom-and-pop size automotive repair shops. But they are often placed away from a plant floor or a mechanic’s garage and frequently do not receive the full maintenance attention that they require.
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Yes, for many industrial and commercial businesses, air compressors play the role of unsung hero – often overlooked until there is a major problem.
Below, Rob Peterson, a 28-year veteran of ExxonMobil Lubricants & Specialties, provides several key maintenance tips that maintenance professionals can use to help extend the lives and maximize the performance of their company’s air compressors.
Basic Safety
Understanding how to manage and maintain compressors and related components safely is an important first step, since it can eliminate a potential liability and improve overall workplace safety. Before working on or around compressors, be sure that the following measures are in place.
First, make sure to follow proper safety lockout, tag-out, and de-energizing procedures.
OSHA regulations require companies to have a lockout/tag-out program to help prevent injuries that can occur when working around equipment that can start-up unexpectedly or release stored energy. Compressors typically cycle on and off without warning, posing a potential hazard. In addition, compressors often have pressurized components that can pack a mighty punch if tampered with under pressure.
To ensure safety when working on compressors, the power supply should be locked out, and all related components depressurized. Each individual working on a compressor should have his, or her, own unique lock applied to an approved power supply lockout device, preventing compressor operation until all locks are removed. A tag should be attached to each lock, identifying its owner.
Safety pressure relief valves are the most important safety devices found on compressors. When properly engineered, installed, and maintained, these valves prevent compressed air from exceeding safe pressure limits.
Should safe pressure limits be exceeded, compressor components and tanks may explode resulting in possible serious injuries. Therefore, safety relief valves must be routinely inspected, tested, and replaced as necessary, to ensure compressor safety. In addition, pressurized components and receiver tanks should have visible pressure gauges, displaying system pressure at all times.
An Original Equipment Manufacturer certification plate should be affixed to all compressors and receiver tanks, stating the maximum allowable working pressure. High-pressure receiver tanks should also display a tag indicating the date of the last hydrostatic pressure test. Such testing and certification is typically done in compliance with the American Society of Mechanical Engineers, Boiler and Pressure Vessel code.
Loss control insurers typically require re-inspection and certification on a periodic basis. It is extremely important to ensure that system operating pressures never exceed certified pressure limits.
Something that is often overlooked but can help improve overall safety, is posting personal protective equipment requirements, such as the need for safety glasses at many points throughout a facility. As is the case in any hazardous environment, specific requirements for personal protective equipment should be clearly posted and enforced.
When dealing with compressed air systems, enforcing the use of safety glasses is highly recommended. This is because an unexpected discharge of compressed air can propel debris into the eye resulting in a lacerated cornea.
Optimizing Compressor Performance
Start by checking for air leaks. Running a compressor with air leaks is like driving a car with the emergency brake on. It not only wastes energy and reduces output capacity; it significantly shortens equipment life and increases maintenance and repair costs. For example, the air leaking from a typical one-eighth inch hole consumes about one horsepower of energy.
Make sure operating pressures are kept at the minimum requirement. This is best accomplished by identifying the maximum application pressure requirement of the system. To this, add the conveyance pressure loss, typically about five PSI required to move air from the compressor to this application. The sum of these two pressures should be the pressure setting of the receiver tank. For example, if the maximum system application pressure requirement is 75 PSI, then the receiver tank should be maintained at 80 PSI. Only minor adjustments should be necessary to fine tune this set point. Never exceed the maximum allowable working pressure stated on the certification plate.
As with air leaks, running excessive pressure results in shortened compressor and component life, along with increased maintenance and repair costs. Increased pressures also result in increased heat, which significantly shortens the life of compressor lubricants, requiring frequent oil changes. Typically, for each two PSI reduction in operating pressure – there will be a one percent increase in efficiency.
To get the most out of your compressor, make sure that intake air filters are routinely replaced and that all induction air piping and manifolds are tight and leak free. This is necessary to ensure that clean intake air enters the compressor, which is crucial to achieving proper component life and compressor efficiency. Periodic white glove inspections of all induction piping surfaces should be performed to ensure that internal surfaces are maintained dust free. The source of any dirt or deposits found should be immediately traced back to the point of origin and repaired.
The Advantage of Synthetic Lubricants
Another area where maintenance professionals can generate significant financial and operational benefits for their company’s air compressors is by using synthetic lubricants.
Compressors generate significant amounts of heat through adiabatic compression. This is the same process used in a diesel engine to ignite diesel fuel. Needless to say, the extreme temperatures encountered in air compressors require lubrication with a product that can withstand such extremes.
Here, the difference between using mineral or synthetic oil can mean the difference between trouble-free operation and having to perform frequent and costly overhauls.
Synthetic lubricants are designed to handle extreme temperatures better than mineral oils. At high temperature extremes, conventional mineral oils can break down, and form harmful deposits, which can foul critical compressor components, resulting in poor performance.
At extremely low temperatures, conventional mineral oils can thicken up and channel preventing proper lubrication at startup. Both extremes can be devastating to compressor life and reliability.
Many compressor manufacturers offer their own line of lubricants. These are often supplied under private label agreements with lubricant manufacturers and blenders. Often, the same or a similar lubricant can be purchased directly from the manufacturer or blender at a considerably reduced price. However, before converting to a different lubricant it is important to evaluate compatibility issues. Here, the expert technical advice of the supplier should be sought. Compatibility testing and any required flushing procedures should be implemented prior to conversion.
Oil Analysis
To ensure optimum lubricant and equipment performance, a routine oil analysis program should be implemented. Such testing should be used not only to identify the condition of the lubricant, but also the presence of any wear metals indicative of a potential developing failure.
The presence of any harmful contaminants such as dirt, water, or coolant should also be identified. An oil analysis program is recommended, through which the user can directly register equipment, specify specific tests and download results. Ideally such a program should be carried out by the lubricant supplier, who is typically best suited to provide proper interpretation of oil condition results.
The key to any oil analysis program is to be able to trend the results. Quarterly oil analysis is recommended for both reciprocating and rotary screw compressors.
Trending samples quarterly should provide information on equipment and lubricant conditions and should be the final verdict on oil change intervals. Testing should include nitration (FTIR), TAN (ASTM D 664), Metals by Inductively Coupled Plasma (ICP) (ASTM D 5185), water content by Karl Fisher (ASTM D 1744), and Particle Count (ISO 4406.2).
By following the key maintenance, operational and safety tips described above, anyone from an industrial plant manager to an automotive service technician can ensure that their air compressors deliver the reliability and performance needed to get the job done safely.