When it comes to air compressor maintenance, focus is usually placed on the consumables, filters, fluids and regulators. Often overlooked are the parts that carry compressed air from the machine itself to the tip of each pneumatic tool. In the compressed air industry, the phrase “Dirty Thirty” is often used in reference to the series of hoses, pipes and fittings — which typically amounts to 30 feet in length between the compressor and the end tool. Here is where pressure drop occurs and can point to factors impacting efficiency.

The Air Compressor Dirty Thirty

When first learning about the Dirty Thirty, operators generally find most surprising that the pressure drop occurring is during that final stretch of hoses. In average scenarios, pressure drop in the Dirty Thirty ranges from 30—50 psi, generally around 20 times the amount of pressure loss occurring along the earlier stages of piping. This is true even in systems where a pipe extends more than 100 feet.

An easy way to inspect the Dirty Thirty for pressure drop is to set up a pressure gauge near the air tool and study the patterns of pressure as the machine operates. If compressed–air applications result in pressure drop, it’s due to upstream limitations in the pipe. It must be noted that a gauge can be slow to read the behavior of such components. A reading could potentially show only a third of the actual pressure loss. Therefore, if a gauge indicates a problem in the 5–psi range, the actual pressure drop might be 15—20 psi.

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How to Improve Efficiency at the Dirty Thirty

Over the last few decades, engineers in general manufacturing plants have taken steps to boost efficiency in compressed air machinery. Two of the most vital goals in this regard have been the elimination of leaks and reduce overall system pressure.

Throughout the process of turning ambient air into compressed air, leaks and pressure drops are problems that can happen at any stage, but most typically occur along the Dirty Thirty. Pressure drops are usually caused by wrongfully sized pipes between the distribution header of an air compressor and corresponding pneumatic tools. Ill–fitting pipes such as these are often the result of oversights on the part of the installers, who typically think in terms of air demand, but don’t consider flow rate.

When an air compressor runs in the ballpark of 100 psig, each 2% reduction in pressure calls for 1% less input. In order to prevent pressure drop, filters and hoses must be selected with respect to their dynamic use instead of the cubic feet per minute they deliver.

Inspect “FRL” Components for Performance Issues

When it comes to the operation of a lubricated air compressor, the cleanest and most reliable compressed air is usually made possible with the use of filters, regulators and lubricators (FRLs) of the point–of–use variety.

The Compressed Air Challenge advises the following FRL maintenance measures:

• Limit filtration and drying to the requisite levels for each given application.
• Only use filters with low pressure drop.
• Ensure that FRLs are sized in correspondence to the system’s flow rate.

Often times, FRLs are found to be too small for the peak flow rates of a given application. In such cases, pressure drop is bound to increase due to the size mismatching between pipes and components. For example, a faulty diagnosis of air pressure levels is a likely occurrence when there’s an 80 psig pressure regulation on the FRL arsenal, but a 50 psig drop due to high–consumption downstream cycles.

In order to keep pressure drop sufficiently low, it’s crucial for FRLs to have routine checkups, and for components to be replaced on an as–needed basis. Often times, the cost of a new FRL component could be far less than the annual expenses that stem from pressure drop. For example, a new filter could run as low as $10, whereas pressure discharge of just 5 psi with a pre–existing filter could amount to an annual operating cost of $1,900.

Prevent Pressure Loss in the Dirty Thirty

Along the Dirty Thirty, pressure drop is often due to quick disconnects and ill–fitted hoses. Trouble with the former is often caused by ball–and–spring assemblies within the female half of the disconnect coupling. Though designed to prevent compressed–air leaks, female quick disconnects can ultimately cause pressure drop.

Equally serious is the loss of pressure that occurs in the hoses that connect an air compressor to assorted end tools. For example, if the hose is 1.4–in., but the system calls for 3.8–in, there isn’t enough width to handle the demands of a given application.

According to the Best Practices for Compressed Air Systems manual by the Compressed Air Challenge, 20 cfm of air at 95 psig through eight feet of 1.4–in. hose results in a nine psi pressure drop. Therefore, a hose must be large enough to accommodate maximum — as opposed to average — airflow rates. For some systems, this means replacing the original hose with something triple in diameter.

Another scenario that can prove problematic is when a lengthier–than–needed hose is used between the compressor and the end tool. Situations like these often occur when a long hose is found for a bargain and selected under the assumption that longer means more bang for the buck. In some cases, a hose will be 10 times the size of what an application requires, leading to a dirty portion well in excess of 30 feet. While the width of the hose should be wide enough to accommodate all pressure levels, length should be limited to the needs of a given application. Accurately sized pipe delivery systems are equally as critical.

In many industrial plants, the amount of leakage in a given application will account for nearly one–third (30%) of the total amount of compressed air being produced. When the cost of energy runs 10 cents per kWh, leakage of 100 cfm can result in a $17,500 annual loss under normal production schedules.

If leaks are an issue with your compressed–air system, the best way to rectify the situation is to isolate the bigger, more obvious leaks first, and then test for smaller, more subtle leaks. As repairs are in progress, test the Dirty Thirty for tiny leaks with an ultrasonic detector. Consult a compressed air expert for large installations and leak testing services.

Consequences of Poor Maintenance Along the Dirty 30

The biggest problems that are commonly found along the Dirty Thirty are pressure loss and air leaks, which lead to issues like faulty applications and less–efficient power usage. When pressure levels are ill–suited to the requirements of an application, the following mishaps are liable to occur:

1. Paint applies unevenly. When a pneumatic paint brush doesn’t receive the right amount of pressure, coatings become uneven, blotched and streaked. Whether you’re painting surfaces made of wood, metal or drywall, the application needs to receive the right amount of pressure to deliver smooth, professional looking coats.

2. Nailers work inconsistently. The purpose of a pneumatic nailer is to send nails into surfaces in under a second with no swinging or hammering required. However, when compressed–air pressure is compromised, the purpose of the nailer can easily be defeated because the applications are rendered less accurate and reliable.

3. Saws don’t cut straight. One of the most hazardous tools is the saw, simply because a slight twitch can lead to an uneven cut, which might ruin a board or panel altogether. The purpose of air–powered saws is to take the strain off joints and muscles and complete cuts in a fraction of the time. Alas, pneumatic saws can be nearly as clumsy as humans when pressure levels are poor.

4. Sanders leave streaks. Sanding by hand is no doubt one of the most strenuous activities in all of woodworking. Therefore, pneumatic sanders are made to eliminate arm strain and — thanks to the orbital motion — deliver finishes instantaneously with a smoothness that no human hand could ever achieve with a sand block. Poor pressure delivery results in streaks and marred finishes.

5. Drills miss. Drilling holes is probably the most sensitive of tasks in furniture assembly, because a crooked or misplaced hole could result in costly replacements. Such concerns can be eliminated, however, with pneumatic drills, which create holes; but only if there’s adequate air pressure.

6. Screws get jammed. The beauty of air–powered tools is that applications that would otherwise be prone to human fault can be carried out in split seconds with no time for nervous ticks, hand slips or arm fatigue. However, insufficient air power can lead to less than perfect results with tools like pneumatic screwdrivers, which must deliver straight, instant applications every time.

7. Polishers don’t shine. When it comes to fine furniture, surfaces look best when they’re polished and smooth. Even if manual buffing is not the most back–breaking of tasks, air–powered polishers are preferable for smooth, professional finishes. Still, the tool needs adequate pressure in order for the surface to get its shine.

8. Grease gets messy. In order for machine joints to work smoothly without grinding or corrosion, grease must be applied evenly on a routine basis. When grease is either applied inadequately or spread inconsistently with splotches and missed spots, parts don’t get properly lubed, but oil deposits can possibly end up in the wrong places. Such are the consequences when the pressure is off in a pneumatic greaser.

9. Staplers wasting staples. On everything from posters to tool boxes, corners and sides must be evenly joined, preferably with no wasted fastener marks or holes. This is why air–powered staplers are much preferable to the manual equivalent, because staples plunge on target without the need for hand pressure and consequent wrist strain. Best of all, no smashed or wasted staples, unless there’s inadequate air pressure.

10. Wrenches lack impact. Few applications can seem as hopeless as the unfastening of old bolts. Likewise, fastening bolts can be a cause of hand and wrist strain, especially if you need to apply dozens within a work shift. Thanks to compressed air-powered versions, screws can be bolted and unbolted in seconds flat with no wrist strain, just as long as the pressurization is right.

11. Jackhammers not breaking ground. Drilling into the ground requires strength, coordination and most importantly a powerful set of tools that can handle rock, clay and all the other possible elements. An air–powered jackhammer is one of the most optimal tools for precision hammering and drilling of spots along rock and concrete surfaces, but the tool won’t work its wonders with inadequate air pressure.

12. Needle scalers leave spots. When it comes to removing rust and layers of paint on hard metals, a needle scaler must work fast and evenly, covering every inch of a given surface without over–scraping any spots. When pressure is poor, however, the overall performance could end up marked with paint spots, scrapes and lingering rust.

13. Rivets ajar. In some forms of construction, jutting fasteners like screws, bolts and nails are considered both unattractive and inconveniently protruding. For such structures, the smooth–headed shapes of rivets are the preferred option for joining panels together. However, without sufficient pressurization, a pneumatic riveter could fail to fasten or deliver things slightly ajar.

14. Angle grinders graze. Sometimes a piece of metal or wood can be just a fraction of an inch off from perfectly fitting with corresponding components. While saws and sanders are often inadequate for such tasks, an angle grinder can trim the excess around corners, edges and on small surfaces, though the tool is unlikely to work very smoothly with subpar air pressure.

15. Blowers sputter. In various industrial settings, the only thing to stop a hot motor from overheating is the consistent breeze of an air blower. When compressed–air blowers are used to keep motors cool, there’d better be no trouble in the Dirty Thirty, or there may be interruptions down the line.

16. Cars with bad coating. No matter how well an engine might run, a car is worth little in the eyes of the typical driver if it lacks a smooth, flawless paint job. However, if the auto shop fails to perform timely maintenance on the air compressor Dirty Thirty, subtle streaks or bubbles might become apparent once you’ve driven off with your freshly painted car.

17. Houses marked with streaks. While not quite the technical undertaking of an automobile paint job, the interior walls and exterior facade of a home are easier to paint with pneumatic sprayers. As a very pressure–sensitive application, however, you’re not going to achieve smooth coats if there’s a pressure drop in the connecting hose.

18. Unstable cabinets. If cabinet shelves aren’t evenly placed, the objects placed within will inevitably slide to the bends of gravity. Therefore, the air–powered tools that screw and hammer cabinet parts into place must be sufficiently pressurized, or else fasteners could get jammed halfway or applied slow enough for human errors to occur.

19. Holes misaligned to corresponding panels and hinges. Few moments are as nerve–racking in a woodworking project as when you need to drill holes into a board or panel piece. With one nervous tick or slip of the elbow, a hole could be placed just millimeters off from the corresponding spacing of a hinge or attachment part. Alas, pneumatic drills can hardly save the day when there’s a pressure drop in the compressed air system.

20. Tables built unevenly. A tabletop is only useful when placed on four solid legs of perfectly even height. Even with all the parts in place, a table could still be wobbly if one of the legs is poorly installed, whether it’s due to a crooked screw/jammed bolt issue, or a stripped drill hole; either of which can happen with ill–pressured tools in hand.

21. Panels joined weakly. Some fasteners hold regardless of whether they go in all the way, others come undone. Such is the case with staples, which can fail to hold boards or anything slightly heavy together when the pneumatic stapler does a poor job due to insufficient air pressure.

22. Steel frames joined insecurely. During building construction, compressed air systems must perform optimally with sufficient pressure for every attached tool. Out of all the tools in the construction arsenal, the riveter is among the most vital because it joins frames together. Alas, an insufficiently powered riveter could result in a weakly joined building frame.

23. Building pieces chipped. If you need to make minor adjustments to the width, contour or overall shape of a small piece of wood or metal, it’s best if the machine does the work for you. However, a pneumatic angle grinder could be just as faulty as the human hand if there’s trouble in the Dirty Thirty.

As air compressors play an increasing role in driving the tools and machinery of industrialized nations, it’s more important than ever that efficiency be maximized and pressure kept optimal throughout all the stages of a compressed–air system. To that end, Quincy Compressor has been a leading innovator in the design and manufacturing of air compressors and connecting tools for nearly a century. Count on Quincy for compressors and air treatment accessories that perform in applications with utmost power and efficiency. To learn more about our compressors and dryers, check out our sales and services page.