A growing number of groups, including manufacturer’s reps, independent auditing companies and energy services companies, offer compressed air auditing services. These services provide valuable benefits to operators of compressed air systems. Generally, you might consider purchasing audit services for one of two reasons.
First, there might be a specific problem in your compressed air system that needs attention. It might be low pressure in a specific part of the plant, moisture in the lines or inadequate overall capacity. The second reason is a desire to reduce compressed air system operating costs. In either case, you should take a number of easy, low-cost actions before the audit begins. If you have a specific issue that needs fixing, these actions might mitigate the problem and preclude the need for costly outside help.
If your desire is to reduce compressed air costs in general, performing these simple tasks will allow auditors to perform a higher-level system analysis. As air auditors, we find that all too often, we spend our time and our client’s money solving problems that only get the air system to a minimum level of operational efficiency. We can’t work on really getting a system working at optimum efficiency until these issues are addressed.
What follows is advice from auditors. Attention to these five points can significantly improve the quality of our auditing or let you avoid calling us in altogether.
1. Focus on filters
These are a critical but often overlooked component of a compressed air system. Frequently, they’re not replaced at appropriate intervals. When filters are clogged, the pressure drop across them literally skyrockets as the filter element reaches the end of its service life. Filters generally operate with a pressure drop between 1 psid and 5 psid. However, as they reach the end of their service life, the pressure drop can exceed 15 psid. This plays havoc with your system and severely limits the air pressure available for air users. Don’t let the pressure problem you’re having on the plant floor come from dirty filters in the compressor room.
Change filters once a year at a minimum. In many facilities, filters must be changed more frequently. To ensure you have the opportunity to change filters before the pressure drop across them skyrockets, install differential pressure gauges on the filters if you don’t already have them. These gauges are available as add-ons to nearly every filter.
Frequently, plant personnel deal with low-pressure problems by increasing the compressor’s output pressure. Remember, for every 2 psig increase in output pressure, energy consumption increases by 1%. The pressure problem might be “solved,” but the underlying issues remain.
2. Locate leaks
A simple fact is that every compressed air system has leaks. Often, a prime reason for calling in an auditor is to perform a leak survey. However, even if a leak survey is part of the audit, make an effort to repair known leaks before the audit starts because auditors don’t get an accurate picture of how the system operates if it has large leaks.
These affect the pressure and flow in an entire compressed air system. During a recent audit, facility engineers complained of pressure problems at a large group of critical air users. Upon further investigation, we found a 1/4-inch leak on a filter/regulator/lubricator (FRL) on the air line servicing the group of equipment. Simply fixing one hole solved the pressure problems for the equipment and increased the pressure available to the other air users.
Pay special attention to quick-disconnects and other hose fittings, the most common place for leaks. Fortunately, they’re also the easiest leaks to repair, often requiring no more than tightening a hose clamp or replacing a quick-disconnect. Inspect and repair connections and quick-disconnects before any air audit.
3. Fix the FRLs
Filter/regulator/lubricators (FRLs) are a critical part of every compressed air system. They protect and lubricate end-use equipment while minimizing the air used. However, FRLs often are in poor operating condition and should be repaired or replaced. First, check the bowls on the filters. If any are cracked or leaking, replace them immediately. If any are full of condensate, drain them and put a system in place so they can drain as needed in the future. If the manual drains on any bowls are cracked open or wide open, close them and inform operators that they shouldn’t be left open. Also, ensure that connections on the FRLs are sound and not leaky.
Second, make sure the regulator gauge is readable and in good working order. As air auditors, we see too many regulator gauges with the housings broken off, gauges filled with condensate, gauges reading zero pressure, gauges that don’t respond when the regulator position is changed, and gauges that have corroded. Replace any regulator that doesn’t display downstream pressure accurately.
Once your regulators are in good working order, make sure they’re set to deliver an air pressure that matches the end-use specifications. Frequently, regulators are set significantly higher than they need to be. They might have been set too high initially or, more likely, machine operators decided that they weren’t getting enough air pressure and have cranked up the regulator.
Common machine operator thinking is, “If I can make 20 widgets a minute with 30 psig, I can make 40 widgets with 60 psig, right?” Alternatively, operators might have had low pressure one day and cranked the regulator pressure up without remembering to reset it. One lesson we’ve learned as air auditors is that after being set initially, regulator pressures go up, but never come back down.
How do you check that your regulators are working properly? Whenever we perform an air audit, we connect a simple digital pressure gauge equipped with a quick-disconnect fitting to verify air pressure on nearly every piece of equipment. Delivering more pressure than end users need increases air consumption.