Don't 'Air' with Your Compressor

Don’t ‘Air’ with Your Compressor

Contributing writer Curt Harler provides an update on air compressor technology and basic maintenance tips to keep yours running efficiently.

Almost every repair shop has a few compressors chugging away. Rather than viewing them as an expense, shops can turn them into moneymakers, or at least less of a drag on the bottom line, by looking at several areas either when buying a new unit or inspecting an old one. New units offer a host of improved features including power savings and better air quality that make them worth considering. However, there’s no reason to toss a perfectly good compressor just because it’s a few years old. Check its operational efficiency — with a close eye to areas such as leak control — and an existing unit will give good service for some time to come.
The latest compressors are package deals that include all the features a shop might need: compressor, refrigeration, drier and filters to remove contaminants from the air. Not only is the package typically cheaper than buying the components individually, but an all-in-one unit takes up less floor space and should cost less to install.

Quality Air
The quality of the air provided is a major factor to consider with new compressors. In general, new units will provide a better supply of clean air than the models of yesteryear. While body shops require high-quality air for painting, an automotive repair shop needs the versatility to run the day-to-day operations from one efficient air supply. These new units provide that.
As the delivery mechanism for operating pneumatic tools, clean, dry air at a consistent pressure is critical. These requirements can be achieved by installing the right compressed air system to meet the needs of the shop’s specific air demand profile. Selecting and installing dryers, filtration and drain traps can be the difference between an expensive impact lasting decades or just a few months.
Several manufacturers offer variable-speed drives that control the rpm of the motor as demand for air increases or decreases. In some cases, these variable-speed drives are called frequency-controlled drives. Either way, the result is similar: the system uses less air and therefore the cost of the electricity used is less.
No matter what the product and no matter who the vendor, correctly designed and installed compressed air distribution systems allow shops and facilities of all sizes to capitalize on energy savings and increase system reliability and productivity. Consulting a trained compressed air system provider will supply both the equipment and design expertise required to achieve these goals.

Piston or Screw?
Any shop owners who announce they’re in the market for a new compressor will be able to kill a lot of time with business associates discussing the relative merits of the piston machine versus the rotary screw machine.
Even manufacturers who produce both types of compressors will agree that it boils down to the kind of application where the ­compressor will be used.
The piston machine is better suited for the typical smaller shop where the demand for air is up and down all day long. A piston compressor is typically better for applications like those in general automotive repair businesses where the demand is cyclical or sporadic. In that kind of shop, air tools are used for a few seconds, set aside, then picked up again a few minutes later.
Rotary screw machines come to the forefront with applications where continuous air is required. The rotary screw compressor will be a tougher, more durable machine for situations where the application calls for a constant-duty cycle. Typically, a paint shop will favor the rotary screw machine as the painter uses the air for longer periods of time and must have a smooth, continuous flow to do an even job with the gun. Likewise, the rotary screw is a better bet for shops that do a good deal of sand or bead blasting.
Tanks and receivers ensure adequate storage. Many mistakenly assume that because rotary screw compressors are 100% duty cycle, tanks aren’t needed. Experts recommend a “wet tank” to provide a first stage of moisture separation and a “dry tank” downstream for true storage. Single tank systems should allow for three to five gallons of storage for every one cfm in air capacity. Wet tanks and multipurpose tanks should include an automatic drain trap. Allowing water to build up in the tank can cause delivery and reliability problems. Pay special attention to the type of drain selected for this component.
But, where demand varies, the piston unit will come to the fore. Besides, the piston machine is typically a mechanically simpler compressor and, therefore, is easier to maintain.

Power Savings
Many businesses, including repair shops, are saving money with power rebates from their electric utility companies. In a lot of cases, a new, energy-efficient compressor will qualify a shop for a rebate that will offset a chunk of the up-front cost of the compressor. Typically, that compressor will have to be a certain horsepower level.
The chance to earn rebates is coming from utilities on both coasts. Power utilities in California, Oregon, Washington State, Connecticut, New Jersey and Massachusetts all offer such programs, and they’re popping up in other states as well. Check out under the Public Service tab for information on your state.
No matter what kind of compressors are being used in a shop, another way to save money on the electric bill is always to start the compressor with the largest motor first every day. Power companies typically base their charges on the highest in-rush kW hour rate, and that rate holds for the remainder of the day.
Say a shop has a half-dozen 5-hp motors and a 50-hp motor. Starting the largest motor first will keep the in-rush rate down. Rather than having the 50 hp added to the 30 hp from the little motors for a total in-rush of 80 hp, starting the 50-hp motor first establishes that 50-hp demand as the largest in-rush and the 5-hp add-ons don’t break the bank.

Lose the Leaks
Another efficiency tip that applies to any compressor system, new or old, is to handle little leaks before they cause a major leak in the corporate checkbook.
Leaks in a well-maintained air distribution system should be no higher than 10% of total compressed air consumption. Because leaks don’t usually stem from a single point, but rather from numerous small leaks in the hundredth- or thousandth-inch range, it may be worthwhile to investigate purchasing or leasing leak detection equipment. Many facilities have found that ultrasonic equipment is extremely effective in locating leaks. In addition, depressurizing the system while not in use will help reduce compressed air loss.
Most leaks occur near the point of tool attachment, either just before the connection or right at it. Those leaks are costly.
Studies indicate that as much as 35% of all compressed air produced is lost to leaks. Inadequately sized piping, artificial demand and other air system design errors can add to unnecessarily high operating costs. Establishing a leak detection and repair program can lead to an efficient compressed air delivery system.
Leaks from the compressed air distribution system cause considerable energy losses and significantly increase operating costs. For example, a quarter-inch diameter hole in an air distribution system operating at 100 psi working pressure will cause an air loss of 104 cubic feet per minute. That’s more than 6,000 cubic feet per hour and, if the system is in continuous operation, over 50 million cubic feet per year. So, with an average energy cost of $0.05 kWh, the annual cost to support a quarter-inch leak is $8,382.
In any case, it pays to have someone in the shop test hoses, tools and equipment regularly for leaks. Problem areas can be quickly and easily identified by using soapsuds or special sprays made for the job.
Check compressed air tools for leaky inlet valves. Another energy hog is the common spiral hose. Spiral hoses should be used only where there’s no other solution because, like pressure regulators, they waste a lot of energy.
Also, check drain traps. Drain traps remove accumulated moisture from clean air treatment components. Drain traps should be included on dryers, moisture ­removal filters and tanks. Capacitance-sensor actuated drains provide excellent value for the money — opening only when needed to release compressed air ­condensate, but not valuable compressed air. It’s also important to note that the moisture collected in these traps may not be suitable for disposal in municipal systems. Cartridge-based condensate management systems provide an easy economical solution to this challenge.

Buying New
There are some nice side-benefits from a new compressor. Whatever the make, model or style of compressor, expect a new unit to be a lot less bothersome than the one it replaces. Most shop owners will be happier with the lower sound or noise level that’s being built into most machines.
Most studies show the number-one end-user requirement related to compressed air is reliability. Compressor downtime means impact wrenches, sanders and other air-driven tools aren’t working. A reliable compressor and a routine maintenance schedule will keep the compressed air system — and all critical shop functions — running smoothly and efficiently.
Expect a new compressor to provide higher duty cycles as well. Couple that with better air quality and markedly improved efficiency, and a new compressor will be a welcome addition to a shop’s equipment closet.
With the benefits from new technology, it would be wise to extend the compressor’s useful life as long as possible. Keeping a compressor in tip-top working order doesn’t require a lot of time. However, it will save a lot of time — and money — if the shop purchases the proper unit to fit its needs and that compressor is well-maintained after installation.
When in doubt about any purchase or use decision, contact a qualified air systems professional. The tool vendor you’ve known for years may be a nice guy, but he may not be the person to design your compressed air system or truly evaluate your shop’s specific needs. A modest investment in the right air system components — and a plan for routine maintenance — can save thousands by maintaining shop productivity and product quality.  


How to Calculate Compressor Piping
The best way to correctly size compressed air piping is to perform specific calculations for the intended system as a whole. This calculation is based on the rule that the maximum pressure drop between the compressor and the air-consuming equipment including dryers, filters and drain traps should be no greater than 14 psi. Here are a few rules of thumb for calculating individual pressure losses:
  Main distribution loop…0.4 psi (0.03 bar x 14.5 = 0.4 psi)
  Branch distribution piping…0.4 psi (0.03 bar x 14.5 = 0.4 psi)
  Drop down connection piping…0.6 psi (0.04 bar x 14.5 = 0.6 psi)
  Dryer…4.0 psi (0.3 bar x 14.5 = 4 psi)
  Filter/regulator/lubricator units and hoses at point of use…9 psi (0.6 bar x 14.5 = 9 psi)
  Total pressure drop…14 psi

Itemizing and detailing air system components and their respective pressure drops creates a much clearer picture. Connection components such as elbows, tees and shutoff valves should also be considered. Furthermore, it’s equally important to determine and consider the equivalent pipe length of the connection components in the overall pipe length.

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