FINDING the right compressor for a specific application can be a minefield for manufacturers, especially with so many different measurements to compare. Wading through L/min, HP, kW and Free Air Delivery (FAD) can leave many who are making purchasing decisions both confused and vulnerable.
Julia Beck, project engineer for the Compressed Air Association of Australia (CAAA), believes manufacturers not only need to understand what the different measurements mean, but also ensure they are getting the right information about their compressors’ output.
“Different companies have different internal protocols for displaying L/min, HP, kW or FAD. While all are quantitative engineering units, they can be tested under different operating conditions, especially loads, which greatly affect the reading,” Beck told Manufacturers’ Monthly.
“This means that an unscrupulous supplier may test its unit at an unrealistically low load to give a higher power output, when it is highly unlikely that the user of the compressor will ever achieve this same efficiency in normal operating conditions.
“Therefore, just stating the power output expressed in HP or kW can be misunderstood by consumers. It’s no good having a large motor if the compressor pump is undersized or inadequate due to sloppy piston and valve tolerances,” she said.
According to Beck, the main factor which should influence the potential use of an air compressor is the amount of compressed air available at the exit port, not necessarily the level of power for the unit. The CAAA therefore advises manufacturers to use the FAD measurement when selecting a compressor, which measures the actual compressed air output of the compressor.
“The FAD system meets AS 4637, so manufacturers can be assured of a consistent reading,” said Beck
“It standardises all the test conditions to ensure that the output measured is realistic and repeatable. Therefore, consumers who look at compressor FAD are comparing apples with apples when it comes to selecting appropriately sized compressors for their application,” she said.
Making cost savings
As well as comparing measurements, accounting for the cost of a compressor also needs to be considered when making a purchasing decision.
Paul Issai from Champion Compressors, says purchasing an air compressor is a major decision with many variables to consider. This decision is further complicated by the vast number of vendors telling you a “different story”.
“The reality is that inadequate compressed air supply can be caused by a number of system faults – an undersized compressor, pressure drops associated with the compressed air reticulation pipe-work and compressed air demand spikes that intermittently exceed the compressor’s output capabilities,” he said.
Issai therefore suggests companies assess the lifetime cost of their compressed air system as a fundamental rule.
“Compressor maintenance and energy costs over a 15yr life accounts for 80% of the total costs, while the purchase cost is about 20% of the lifetime costs. For example, a typical standard 7.5kW compressor costs approximately $6,500 to purchase and will incur operating costs of approximately $24,500 over its 15yr life (at 3,100 hours/year, $0.10/kWh, 0.7 load factor),” said Issai.
“Unfortunately, many companies are trapped in the philosophy that they need to purchase the cheapest air compressor available, making their decision based solely on equipment purchase costs.
“A company’s decision should be based on the principle of buying a compressor to achieve the lowest lifetime cost for their business, factoring in design of equipment, power costs, service costs, preventative maintenance, possible downtime and operational efficiencies,” he said.
A regular and effective maintenance and air audit program is also vital in achieving energy and cost savings.
According to Issai, a thorough audit of any industrial compressed air system can “reveal surprising opportunities to save on running costs”, as pneumatic power is relatively costly.
“It’s not possible to simply look at a compressor at any point in time and completely diagnose how it is performing. The operation of the compressor changes in sympathy with the air demand.
“The air audit is therefore an essential tool for assessing compressed air system performance and potential improvements. We recommend monitoring the compressor over a seven-day cycle,” he said.
Finally, Issai emphasises that poorly maintained systems negatively impact a company’s bottom line, making regular maintenance a strong imperative.
“The opportunity to save energy and money is not limited to the compressor itself. Dust can clog the pre-filter, air-intake filter, oil filter and air/oil separator. For every 1kPa of clogging, efficiency is reduced by 1%,” Issai said.
Compressed Air Association of Australia - www.amei.com.au.
Champion Compressors 1800 810 015.