Your eyes are often bigger than your stomach

A report card on compressed air knowledge: Part 2

By Michael Camber

Missed part 1?

Click here for the results of a recent quiz of automotive service shops about compressed air.

The point least understood among the surveyed compressor users is how to size a system for the shop.  We presented a scenario with five techs, each using 15 cfm tools, and gave five different compressor size (hp) options. Less than 40% picked the most appropriate option, and most incorrect answers were heavily over-sized.  We see this in the field all the time.  Operators routinely overestimate the size of compressor needed.

Depending on the type and design efficiency, most commercial/industrial compressors produce between 3 and 4.5 cfm per horsepower.  The (simplistic) quiz scenario assumed all air users would need air simultaneously.  Using 4 cfm/hp, a 20 hp compressor with 100% duty cycle would supply air to all five users.  As mentioned above, 40% chose this option, but another 40% chose either the 30 or 50 hp options. 

The downsides to oversizing include:

  • spending more up-front for the equipment (compressors, dryers, etc)
  • paying more for parts and service
  • increased wear from over-cycling (starts and stops)
  • reduced energy efficiency (this applies more to rotary type machines than pistons, which mostly operate on start/stop controls)

Now factor in the reality that it is very rare for all techs to be operating air tools at the same time.  So let’s say only three of five people will be using air simultaneously (total of 45 cfm).  A 15 hp compressor would easily handle it.  If only two out of five were using air at the same time, an efficient 7.5 hp with 100% duty cycle might suffice.  Or bump it to 10 hp (40 cfm) and add 100-200 gallons of storage to be safe.  Far more cost effective than buying the 20 hp.

For energy efficiency, it would be better to get two smaller machines than one large one. This also give you back-up, but it does drive up the initial cost.

If you anticipate that you will need more air in the future,  arrange your compressor room/area to allow for additional machines, but only buy what you need in the short term.  The money you save on energy and service will help pay for the upgrade later.

Download our Compressed Air System Installation Guide E-book for more installation tips.

A Report Card On Compressed Air Knowledge

By: Michael Camber

One of our media partners recently quizzed their subscribers to assess users’ knowledge about compressed air systems.  The respondents were in the automotive service industry, but the questions were not industry or application specific and the answers are a fair reflection of compressed air knowledge of most businesses with compressors 25 hp and below.  We thought it would be useful to present the results and discuss areas where understanding of compressed air systems needs a boost.

Duty Cycle

A strong majority (84%) of respondents knew that reciprocating/piston type compressors operate at higher internal temperatures than rotary type compressors, but nearly 1/3 mistakenly thought that shop recips could safely run at 100% duty cycle.  Some recips are built to run at higher duty cycles than others, but all air-cooled units need at least some downtime to cool off.  The consequences of overrunning them include loss of lubrication, seizure, motor failure and higher oil carry-over into paint and equipment.

Check out our Piston vs. Rotary Screw Infographic for a quick comparison.

Piping Material Choices

Regarding piping, nearly 2/3 know that copper or aluminum are better choices– especially if air quality is important– but a full 20% picked PVC as top choice.  While PVC doesn’t accumulate or add contaminants, it presents one major problem:

Wait for it ….

Yes, PVC is less safe than any metal pipe and is subject to rupturing and fragmenting.

Solving Pressure Problems

When presented with five possible solutions for solving a low pressure problem, everyone recognized that buying another (or larger) air compressor to get more flow is not the first step to address the problem.  Checking for leaks, checking pipe size, adding storage and doing a pump-up test to check compressor function were all known to be better first steps.  We were pleased to see that over 80% recommended doing all of these things before buying another compressor to get more flow (cfm).

Filters Are Not Dryers

Likewise, we were pleased to see that everyone knew that a compressed air dryer is a simple solution to address the common summertime problem of increased water in compressed air lines and tools.  It’s apparent though that not everyone understands the difference between dryers and other devices that remove some moisture. Filter style moisture separators (with drain valves) are effective at removing liquid water.  Storage tanks do the same and can allow some moisture vapor to cool and condense to liquid, but the key to effective drying is reducing the compressed air pressure dew point below the ambient temperature.  Tanks and filters cannot do it. A dryer can.

The last quiz question was about compressor sizing. Since this topic is a bit more complex it deserves its own post. Stay tuned…

Resolve to Learn

By: Michael Camber

New year – new me” Does that sound familiar? At the start of the new year, many of us are turning our attention from the accomplishments of the past year to new goals and resolutions for the year ahead.

Here at Kaeser, we strongly believe in ongoing professional development both for our own employees and our customers. The more we know, the better we can advise and support our customers. This is why Kaeser Compressors’ training department holds close to 100 internal training classes a year (that is just in the US). In 2018 alone we spent 215 days in a classroom. That’s a big investment in education.

Beyond that, we are always encouraging our customers to learn more, dive deeper, and think outside the box regarding their compressed air, vacuum and blower systems. The more you know about compressed air, the more efficiently and reliably you can make it.

To that end we have teamed up with several industry media partners to present free webinars throughout the year to share lessons learned and best practices from compressed air and blower experts. Here is a schedule of events:

You can register to attend the live session, or if you prefer, watch the archived version as your schedule allows. Many webinars offer additional resources for download that pertain to the webinar topic and you can usually download the slides as well.

Want to educate yourself on other industry topics? These publications produce many webinars on a number of topics for your plant and are conducted by industry experts. While the presenters typically have an affiliation with a solution provider, the media hosts ensure the webinars are educational in nature and are not a sales push. Here are some industrial magazines’ webinar pages to take a look at:

Registration isn’t open for all the webinars yet, so we will update this post as registrations open. Subscribe to our blog (look for the “Follow via email” button at the top right of this page) to get updated on when registration opens or take some time and look at some of our archived webinars here.

We hope education is a goal for you in 2019 and that you will join us at one of our webinars this year. We would also appreciate hearing other goals you have for 2019, and if you have any recommendations on webinars you’ve found helpful, please share with us as well.

CAGI: Helping you pick the good apples

By: Michael Camber

For decades, compressor manufacturers found creative ways to present their energy consumption in the most favorable light when up against competitors.  Some were more scrupulous than others, but often the customer did not get the best value possible.

In the late 1990s— to forestall potentially cumbersome government regulations— the Compressed Air and Gas Institute and its compressor manufacturer members worked together to agree upon standards for measuring the energy efficiency of compressors and a format for publishing it so that buyers and specifiers could make fair comparisons when selecting compressors.  The product of this effort is commonly known as the “CAGI datasheet” (see example below), and we’ve written about this before. The datasheets enable better apples-to-apples comparisons, and they can be helpful in providing documentation necessary for some utility rebate programs.

Sample CAGI datasheet for Kaeser's CSD 125 air compressor
Sample CAGI datasheet for Kaeser’s CSD 125 air compressor

They further agreed to test protocols and developed a Performance Verification Program in which participating members’ products are periodically and randomly selected for testing by a third party to verify the performance data that manufacturers published in the CAGI datasheets format. Participation is voluntary and open to all manufacturers, whether they are CAGI members or not.

Participants may publish a  decal on compressors as well as product literature, web pages, etc.

The key thing to be aware of is that manufacturers should not publish performance in the official format shown above or in any way present the Performance Verification logo unless they officially participate in the program and are in good standing.  As of this writing, only 9 out of 21 members of CAGI’s Rotary Positive compressor section are currently participating in the Performance Verification Program. By the way, the CAGI program is the only one of its kind.  I mention this because we’ve seen some creative marketing out there that implies government certification of product performance.

If a participating member’s products fail to measure up to published performance three times in a five year period, that manufacturer is suspended from the program for a minimum period of six months and should not present customers with CAGI datasheets or represent that they are participants in the Performance Verification Program.

If energy efficiency is important when selecting compressors, you owe it to yourself to get the product’s current CAGI datasheet and confirm the manufacturer is a current participant in the program (on the CAGI website).

Learn more about CAGI’s verification program in this video:

Additional resources:

  1. White paper: CAGI Data Sheets: An apples to apples comparison
  2. CAGI’s Performance Verification Program

What is a Flow Controller and What Does it Do?

By: Wayne Perry

A flow controller is essentially a pressure regulator that reacts very quickly to changes in downstream demand, releasing volumes of stored compressed air with precision to maintain very stable system pressure. Given adequate storage upstream, they can maintain system pressures within +/- 1 psig of target pressure even with large swings in demand. Too often, system pressure is set higher than needed to allow for fluctuation. With the precision flow controls, the target pressure setting can be reduced to the minimum required for the end uses.

Flow controllers present several significant energy savings and operating benefits, especially in older existing plants that don’t have the capital budgets available for major compressed air system re-designs. In many of these cases, system capacity is no longer well-matched to production demands.

By lowering the system pressure to its minimum, artificial demand is reduced. Further, the volume of air the compressors must produce is also reduced, so that leaks and other unregulated uses will consume less air. This is especially advantageous for installations with older piping where it may not be feasible to repair or upgrade the air distribution system. Given that the average compressed air system will leak about one third of the total air volume and unregulated uses can account for another one third, or more of total volume, this reduction in pressure can affect more than half of the total air supply. For example, if the downstream pressure can be dropped from 100 psig to 80 psig, and half of the demand is unregulated, the volume required to support the system will drop by about 10%. In a system using 2500 cfm, the drop in artificial demand (250 cfm) is equal to a 50 hp compressor. This is a conservative number since it is common that more than half of the system demand is unregulated.

In addition to reducing artificial demand, a flow controller can be used to support large intermittent demand events (like bag house purges) that might otherwise draw down the system pressure and even cause an additional compressor to start in order to rebuild the pressure.

The chart below shows a compressed air system before and after installing a flow controller.

Figure 1a

In this case, the plant was having problems with pressure swings and their supply was not quite able to meet demand. Their assumption was that a new air compressor was needed. Instead, a flow controller was installed and they were able to achieve a dramatic reduction in system pressure: from 82 psig to 69 psig, resulting in 6-1/2% power cost savings. This demand-side pressure reduction also reduced air loss due to leaks and unregulated usage by more than 13%—without fixing a leak. Adding the 6-1/2% savings from reducing the power, the 13% from the leaks, and an additional 3 – 4% for increased tool efficiency brings the total savings closer to 24%.

Another positive effect of using a flow controller to stabilize system pressure is an increase in productivity. With more stable system pressure, pneumatic devices operate more consistently, efficiently, and predictably. Nut runners, for example, will produce the same torque operation after operation with a stable pressure. Production machines will not alarm or stop due to fluctuations in system pressure. Product quality will improve. In some applications, stabilizing the air pressure has major production benefits that outweigh even large energy savings.

New installations, with today’s advanced electronic system controls, can achieve these benefits of pressure control without the use of flow controls. In many older systems, however, the flow controller offers stable system pressure without the need for advanced communications protocols—a huge benefit for systems that do not have the ability to easily connect with modern master system controllers.

This blog entry is an excerpt from our white paper, “The Proper Application of Pressure/Flow Controls”. To learn more, download the full version of the white paper here.