Over the weekend I was working on a car in my driveway and I needed a large volume of air at the far end of the car to try and unplug a clogged sunroof drain line. Rather than trying to move the car while it was mostly taken apart, I just hooked up another air line extension and started to go to the drain. Even knowing what I know as an EXAIR Application Engineer about lengths of tubing, air restriction, and fitting restrictions, I went ahead with the quick and easy “fix”.
I grabbed another 30′ – 3/8″ i.d. air line with 1/4″ quick disconnects (see why this is wrong with this blog) on both end, rather than getting out the 50′ long 1/2″ i.d. air line that I have with proper fittings that then reduce down to a 1/4″NPT at the end to tie into most of my air tools. By doing so I ended up hooking up a Safety Air Gun which then gave a very light puff of air into the tube and the clog in the line went nowhere. As a matter of fact, it was almost like it laughed because the tubing vibrated as if the clog said, “Pfft I am going nowhere.”
I then, stepped back and evaluated what I had done in a rush to try and get a job done rather than taking the extra five minutes to get the proper air line to do the job. I then spent 10 minutes putting that hose up and getting out the correct hose. Then, with a whoosh and a thud the clog was launched into my yard from the clogged drain port and I finished the repairs.
If only I had watched Russ Bowman’s spectacular video on Proper Compressed Air Supply Plumbing the day before. Rather than wasting time with the quick “fix” that cost me more time and didn’t fix anything I should have taken a little more time up front to verify I had properly sized my lines for the job at hand.
If you would like to discuss compressed air plumbing, appropriate line sizes, or insufficient flow on your compressed air system, please contact an EXAIR Application Engineer.
“To measure is to know – if you cannot measure it, you cannot improve it.” -Lord Kelvin, mathematical physicist, engineer,and pioneer in the field of thermodynamics.
This is true of most anything. If you want to lose weight, you’re going to need a good scale. If you want to improve your time in the 100 yard dash, you’re going to need a good stopwatch. And if you want to decrease compressed air consumption, you’ll need a good flowmeter. In fact, this is the first of six steps that we can use to help you optimize your compressed air system.
There are various methods of measuring fluid flow, but the most popular for compressed air is thermal mass air flow. This has the distinct advantage of accurate and instantaneous measurement of MASS flow rate…which is important, because measuring VOLUMETRIC flow rate would need to be corrected for pressure in order to determine the true compressed air consumption. My colleague John Ball explains this in detail in a most excellent blog on Actual (volume) Vs. Standard (mass) Flows.
So, now we know how to measure the mass flow rate. Now, what do we do with it? Well, as in the weight loss and sprint time improvements mentioned earlier, you have to know what kind of shape you’re in right now to know how far you are from where you want to be. Stepping on a scale, timing your run, or measuring your plant’s air flow right now is your “before” data, which represents Step One. The next Five Steps are how you get to where you want to be (for compressed air optimization, that is – there may be a different amount of steps towards your fitness/athletic goals.) So, compressed air-wise, EXAIR offers the following solutions for Step One:
Digital Flowmeter with wireless capability. This is our latest offering, and it doesn’t get any simpler than this. Imagine having a flowmeter installed in your compressed air system, and having its readings continually supplied to your computer. You can record, analyze, manipulate, and share the data with ease.
Digital Flowmeter with USB Data Logger. We’ve been offering these, with great success, for almost seven years now. The Data Logger plugs into the Digital Flowmeter and, depending on how you set it up, records the flow rate from once a second (for about nine hours of data) up to once every 12 hours (for over two years worth.) Pull it from your Digital Flowmeter whenever you want to download the data to your computer, where you can view & save it in the software we supply, or export it directly into Microsoft Excel.
Summing Remote Display. This connects directly to the Digital Flowmeter and can be installed up to 50 feet away. At the push of a button, you can change the reading from actual current air consumption to usage for the last 24 hours, or total cumulative usage. It’s powered directly from the Digital Flowmeter, so you don’t even need an electrical outlet nearby.
Digital Flowmeter. As a stand-alone product, it’ll show you actual current air consumption, and the display can also be manipulated to show daily or cumulative usage. It has milliamp & pulse outputs, as well as a Serial Communication option, if you can work with any of those to get your data where you want it.
Stay tuned for more information on the other five steps. If you just can’t wait, though, you can always give me a call. I can talk about compressed air efficiency all day long, and sometimes, I do!
Leaks in a compressed air system can waste thousands of dollars of electricity per year. In fact, in many plants, the leakage can account for up to 30% of the total operational cost of the compressor. Some of the most common areas where you might find a leak would be at connection joints like valves, unions, couplings, fittings, etc. This not only wastes energy but it can also cause the compressed air system to lose pressure which reduces the end use product’s performance, like an air operated actuator being unable to close a valve, for instance.
One way to estimate how much leakage a system has is to turn off all of the point-of-use devices / pneumatic tools, then start the compressor and record the average time it takes for the compressor to cycle on and off. The total percentage of leakage can be calculated as follows:
Percentage = [(T x 100) / (T + t)]
T = on time in minutes
t = off time in minutes
The percentage of compressor capacity that is lost should be under 10% for a system that is properly maintained.
Another method to calculate the amount of leakage in a system is by using a downstream pressure gauge from a receiver tank. You would need to know the total volume in the system at this point though to accurately estimate the leakage. As the compressor starts to cycle on, you want to allow the system to reach the nominal operating pressure for the process and record the length of time it takes for the pressure to drop to a lower level. As stated above, any leakage more than 10% shows that improvements could be made in the system.
(V x (P1 – P2) / T x 14.7) x 1.25
V= Volumetric Flow (CFM)
P1 = Operating Pressure (PSIG)
P2 = Lower Pressure (PSIG)
T = Time (minutes)
14.7 = Atmospheric Pressure
1.25 = correction factor to figure the amount of leakage as the pressure drops in the system
Now that we’ve covered how to estimate the amount of leakage there might be in a system, we can now look at the cost of a leak. For this example, we will consider a leak point to be the equivalent to a 1/16″ diameter hole.
A 1/16″ diameter hole is going to flow close to 3.8 SCFM @ 80 PSIG supply pressure. An industrial sized air compressor uses about 1 horsepower of energy to make roughly 4 SCFM of compressed air. Many plants know their actual energy costs but if not, a reasonable average to use is $0.25/1,000 SCF generated.
3.8 SCFM (consumed) x 60 minutes x $ 0.25 divided by 1,000 SCF
= $ 0.06 per hour
= $ 0.48 per 8 hour work shift
= $ 2.40 per 5-day work week
= $ 124.80 per year (based on 52 weeks)
As you can see, that’s a lot of money and energy being lost to just one small leak. More than likely, this wouldn’t be the only leak in the system so it wouldn’t take long for the cost to quickly add up for several leaks of this size.
If you’d like to discuss how EXAIR products can help identify and locate costly leaks in your compressed air system, please contact one of our application engineers at 800-903-9247.
Many times when we provide the air consumption of an EXAIR product, we get a response like…. “I’ve got plenty of pressure, we run at around 100 PSIG”. While having the correct pressure available is important, it doesn’t make up for the volume requirement or SCFM (Standard Cubic Feet per Minute) needed to maintain that pressure. We commonly reference trying to supply water to a fire hose with a garden hose, it is the same principle, in regards to compressed air.
When looking to maintain an efficient compressed air system, it’s important that you use properly sized supply lines and fittings to support the air demand (SCFM) of the point-of-use device. The smaller the ID and the longer the length of run, it becomes more difficult for the air to travel through the system. Undersized supply lines or piping can sometimes be the biggest culprit in a compressed air system as they can lead to severe pressure drops or the loss of pressure from the compressor to the end use product.
Take for example our 18″ Super Air Knife. A 18″ Super Air Knife will consume 52.2 SCFM at 80 PSIG. We recommend using 1/2″ Schedule 40 pipe up to 10′ or 3/4″ pipe up to 50′. The reason you need to increase the pipe size after 10′ of run is that 1/2″ pipe can flow close to 100 SCFM up to 10′ but for a 50′ length it can only flow 42 SCFM. On the other hand, 3/4″ pipe is able to flow 100 SCFM up to 50′ so this will allow you to carry the volume needed to the inlet of the knife, without losing pressure through the line.
We also explain how performance can be negatively affected by improper plumbing in the following short video:
Another problem area is using restrictive fittings, like quick disconnects. While this may be useful with common everyday pneumatic tools, like an impact wrench or nail gun, they can severely limit the volumetric flow to a device requiring more air , like a longer length air knife.
For example, looking at the above 1/4″ quick disconnect, the ID of the fitting is much smaller than the NPT connection size. In this case, it is measuring close to .192″. If you were using a device like our Super Air Knife that features 1/4″ FNPT inlets, even though you are providing the correct thread size, the small inside diameter of the quick disconnect causes too much of a restriction for the volume (SCFM) required to properly support the knife, resulting in a pressure drop through the line, reducing the overall performance.
If you have any questions about compressed air applications or supply lines, please contact one of our application engineers for assistance.
Both gas and liquid flows can be measured in volumetric or mass flow rates. With non-compressible liquids these two measurements are very nearly the same sans the effects of temperature. With compressible gasses though, they are very different. The same mass under different pressures will occupy dissimilar volumes.
To demonstrate this, take a folded fluffy comforter and weigh it. Then stuff into one of those storage bags that you suck down with a vacuum cleaner. The physical size becomes very much smaller but the weight (mass) stays the same.
When measuring a flow of a compressible gas through a pipe you are measuring volumetric flow. Unlike non-compressible liquids, it is of little value unless it is converted to mass flow which would be dictated by the pressure it is under. For example the utility company charges by the cubic foot of natural gas and gallons for water. With water you actually get a gallon as measured by the meter. With gas though, the mass you receive depends on pressure it is under.
To effectively measure gas flows, their volumetric flow rate has to be converted to standard conditions for temperature and pressure. Simply put, it is the volume it would occupy at atmospheric pressure (14.7 psi) and defined as standard cubic feet per minute (SCFM).
Convert flow from CFM to SCFM
Qg = Q x P/14.7
Qg=Gas flow in standard cubic feet per minute (SCFM)
Q=Volume flow rate in cubic feet per minute (CFM)
P=Line pressure absolute (gage pressure +14.7).
Example: Convert gas flow expressed in cubic feet per minute (CFM) to units of standard cubic feet per minute (SCFM).
Q = 20 CFM
P = 114.7 (100 psi gage reading +14.7)
Qg = Q x P/14.7 = 20 CFM x 114.7/ 14.7 = 156 SCFM
Flow meters used to measure gasses usually are calibrated for readings at atmospheric pressure. When the flow is under pressure, they provide a chart of factors associated with various pressures to multiply against the visual reading.