If you use compressed air for ANYTHING, odds are EVERYTHING you use it for has a minimum supply pressure for proper operation. And if the supply pressure drops below that:
Blowoff devices won’t develop enough flow & force to effectively clean or dry the object(s) you use them for.
Air-operated chucks on CNC machines won’t hold the piece steady enough for proper cutting, and tool changers will operate slowly/sluggishly. This is a bad combination…increasing the time it takes to make something, AND making it poorly.
Pneumatic cylinders will actuate slowly…if at all. This can cause a big problem if, for instance, they’re used to lift a lid on a mixing tank for an automated chemical add, which ends up pouring all over the partially closed lid of the tank instead of going inside it.
These are just a few of the problems that inadequate supply pressure can lead to, and I list them specifically because I experienced them all during my storied (and strange) career path before EXAIR made me the compressed air know-it-all expert I am today. It wasn’t my job to fix those problems (I was on site doing field service on a scale, a hydraulic motor, and a chemical pump, respectively), so I had no idea HOW to fix the compressed air-related problems…but I do now.
One quick & easy fix would have been to increase the compressor discharge pressure. That’d work just fine, but it comes with a cost. Every 2psi increase in discharge pressure increases the power consumption of the compressor’s motor by 1%. Let’s say you increased the discharge pressure from 100psig to 120psig – that’s a 10% increase in power consumption…and operating cost. To add insult to injury, that also increases the magnitude of any leaks in your system, making them more costly as well.
EXAIR Model 9500-60 60 Gallon Receiver Tank.
Actually, that probably IS what I’d have done as a scale, hydraulics, or industrial pump technician. The RIGHT answer, though, is intermediate storage. A properly sized Receiver Tank, located close enough to those operations, would have prevented those problems without increasing operating costs. In fact, it could have even brought them down, if the compressed air header pressure was already set to overcome any pressure drops on the way to those air guns, CNC machine, or mixing tank lid cylinders. Every 2% DECREASE in discharge pressure will also decrease the compressor motor’s power consumption by 1%. Which is actually Step 6 in our Six Steps To Optimizing Your Compressed Air System.
You electrical-types out there could also think of it as a capacitor – absorbing demand spikes & helping the circuit run more evenly.
Sizing a Receiver Tank is fairly straightforward, and we’ve written about it here, here, and here. You can, of course, always contact an Application Engineer to do (or check) the math…give me a call.
Russ Bowman, CCASS
Application Engineer Visit us on the Web Follow me on Twitter Like us on Facebook
If there’s one thing I’ve learned about compressed air, it’s that pressure is a lot like coffee. A little bit gets the job done, but too much just makes you jittery and costs you more than it should. The last step in our 6 Steps to Optimizing Compressed Air series is all about dialing that pressure back to where it actually needs to be. So why worry about pressure?
Compressed air is one of the most expensive utilities in your facility. For every couple of PSI you crank the system higher than necessary, your energy bill climbs right along with it. In most cases, your application doesn’t even need that extra pressure. It’s like using a fire hose to water a houseplant.
This is where pressure regulators come in. They’re simple devices, a knob, a spring, a diaphragm, but they’re doing some heavy lifting. Twist the knob, and the spring loads or unloads. That changes how much the diaphragm allows through, and suddenly you’ve got a steady, consistent downstream pressure without overfeeding your air tools or EXAIR products.
The real magic happens when you lower that setpoint. If your Super Air Knife is blowing water off parts just fine at 60 PSIG, why run it at 100 PSIG? Less pressure means less flow, and less flow means more savings. You’ll get the same result with a smaller demand on the compressor. That’s a win-win every plant manager can appreciate.
Now, before you start cranking down knobs all over the place, keep sizing in mind. Regulators need to be matched to the volume of air your application requires. If they’re undersized, you’ll experience droop, when the pressure drops off during demand spikes. EXAIR takes the guesswork out by offering properly sized regulators in kits with a lot of our products. We’ve already done the math so you don’t have to.
Turning down the pressure might be the last of the six steps to optimizing compressed air, but it’s one of the easiest changes to make and one of the fastest ways to save. A couple twists of the regulator could be all it takes to lighten the load on your compressor, cut operating costs, and keep your system running lean and efficient.
And if you’re not sure where to start, that’s what our Application Engineers are here for. Call us, chat with us, or shoot us an email. We’ll help you find the right pressure for your setup without the trial and error.
EXAIR is now partnering with EasyCAS by DirektIn software. This tool lets you actually measure and validate the savings you’re getting from steps like lowering pressure and implementing engineered solutions. No more guessing, you’ll have hard data showing how much air and money you’re saving.
If you’re reading the EXAIR blog, odds are you’re interested in getting the most out of your compressed air system. While using engineered compressed air products is certainly one of the best ways to do that (see our Six Steps To Optimizing Your Compressed Air System), there are some things you can look at on the supply side as well. One such metric – and a key one, at that – is isentropic efficiency.
In a nutshell, isentropic efficiency is a measure of how well an air compressor converts the electrical energy it consumes into compressed air. The basic formula is a ratio between the compressor’s actual performance to that of an ideal compression process. Mathematically, it’s expressed as:
Now, as long as air compressors have moving parts, the actual energy consumed will always be higher than the amount of energy required for an ideal process. That’s because the ideal process ignores inescapable losses due to friction between – and inertia of – moving parts, electrical losses (motor efficiency), pressure drops, and heat of compression. So, like any other machine or engine, you’ll never get 100% efficiency.
It’s still a great idea to look for the highest efficiency. So great, in fact, that the U.S. Department of Energy, just this month, began efficiency regulation for oil-flooded rotary air compressors, meaning these compressors will have to meet minimum standards of isentropic efficiency. Specific Power used to be the standard by which an air compressor’s efficiency would be evaluated. It’s the ratio of power consumption to the amount of compressed air produced, normally expressed as kW/100CFM. That doesn’t take the compressor discharge pressure into consideration, which does indeed affect the power needed to generate a given amount of compressed air. We know that a 2psi pressure change will result in a 1% change in power consumption. So, if one manufacturer reports the Specific Power as kilowatts per 100 CFM @100psig, and another reports it as kilowatts per 100 CFM @140psig, that 40psi difference means a 20% variance.
Now, that doesn’t mean we stop using Specific Power – it’s one of the two variables in the isentropic efficiency equation. The other being, of course, the discharge operating pressure:
Where:
16.52 and 0.2857 are constants
p2 is the discharge operating pressure (psig)
14.5 is atmospheric pressure (psi) – this corrects gauge pressure to absolute pressure
P2 is Specific Power
The Compressed Air & Gas Institute (CAGI) publishes data sheets that are analogous to the fuel efficiency stickers on new car windows. Here’s a sample of one:
And, using the isentropic efficiency formula:
We get an isentropic efficiency of 86.50% (close enough to the CAGI Data Sheet’s 86.47%; likely due to a significant figure discrepancy in the calculations), which is pretty good. The highest published isentropic efficiency is about 92%. At EXAIR, our mission is to help you get the most out of our products and your compressed air system. If you have questions, we’ve got answers – give me a call.
Russ Bowman, CCASS
Application Engineer Visit us on the Web Follow me on Twitter Like us on Facebook
If you’re a follower of the EXAIR Blog, you’re probably well aware that compressed air is the most expensive utility in an industrial environment. The average cost to generate 1000 Standard Cubic Feet of compressed air is $0.25. If you’re familiar with how much air you use on a daily basis, you’ll understand just how quickly that adds up. To make matters worse, many compressed air systems waste significant amounts of compressed air just through leaks. According to the Compressed Air Challenge, a typical plant that has not been well maintained will likely have a leak rate of approximately 30%!! Good luck explaining to your finance department that you’re carelessly wasting 30% of the most expensive utility. To make sure you get the most out of your compressed air system, it’s important to follow the Six Steps to Optimizing Your Compressed Air System.
Starting with Step 1: Measure the air consumption to find sources that use a lot of compressed air. In order to have an understanding of your compressed air usage across various processes and in your entire facility, you have to measure and produce a baseline. Without a measurement of usage, there’s no way to determine your actual costs or evaluate opportunities for savings. To do so, EXAIR offers a range of Digital Flowmeters from stock. The Digital Flowmeter provides a digital readout of the exact amount of compressed air being used. Many companies will install the DFM on each major leg of their air distribution system to allow for constant monitoring and provide a benchmark of compressed air usage.
Once you’ve measured your baseline, it’s time to explore another simple avenue of savings. Step 2 in the process is finding and fixing leaks in your current system. EXAIR offers our Model 9061 Ultrasonic Leak Detector to allow you to locate and fix any leaks within your distribution system. With an unmaintained system wasting on average 30% of the produced volume, this one seems like a no-brainer but is often overlooked. If you can hear the leak without the help of a device like the ULD, it’s a VERY bad leak. These should be located, tagged, and repaired ASAP!
After getting a baseline measurement of the air consumption in your facility of compressed air usage and locating and fixing leaks in your system, it’s time to begin implementing some changes. Step 3 of the 6 Steps to Optimizing Your Compressed Air System covers upgrading your blowoff, cooling, and drying operations using engineered compressed air products. EXAIR manufactures a variety of products that can help to ensure you’re using your compressed air in the best way possible. While it may seem simple, easy, and cheap to use something like an open-ended pipe or tube for blowoff, the fact of the matter is that the volume of air that these homemade solutions use quickly make them more expensive. Look no further than EXAIR when seeking a safe, efficient, and reliable engineered blowoff solution.
EXAIR Intelligent Compressed Air Products such as (left to right) the Air Wipe, Super Air Knife, Super Air Nozzle, and Air Amplifier are engineered to entrain enormous amounts of air from the surrounding environment.
Step 4 may be the easiest of any of the others. TURN IT OFF! You can’t waste compressed air when it’s turned off. By strategically placing valves at various points throughout the distribution system, it allows you to isolate areas of the facility that may not require continuous compressed air usage. It isn’t exactly feasible to eliminate every single leak, so even if you’ve closely followed Step 3 it’s still beneficial to close some valves here and there to further reduce your consumption. In some applications, such as products traveling on a conveyor, it may be possible to utilize a product like EXAIR’s Electronic Flow Controller to ensure air isn’t wasted in between parts on the conveyor.
The 5th step in the 6 steps to optimizing your compressed air system highlights the use of intermediate storage of compressed air near the point of use. Receiver tanks are installed in the distribution system to provide a source of compressed air close to the point of use, rather than relying on the output of the compressor. Compressed air receiver tanks are an integral part to many compressed air distribution systems. Compressed air is stored at a high pressure after drying and filtration, but just upstream of point of use devices. The receiver tank is charged to a pressure higher than what is needed by the system, creating a favorable pressure differential to release compressed air when needed.
Think of a compressed air receiver tank as a “battery”. It stores the compressed air energy within a system to be used in periods of peak demand, helping to maintain a stable compressed air pressure. This improves the overall performance of the compressed air system and helps to prevent pressure drop. They should be placed strategically to provide a source of compressed air to intermittent high-volume applications.
The last step, Step 6, discusses the use of pressure regulators at the point of use. Pressure regulators are available to control the air pressure within the system and throttle the appropriate supply of air to any pneumatic device. As the last of the six steps to optimizing your compressed air system, controlling air pressure so that you’re only consuming as much as necessary can have a dramatic impact. EXAIR sells a variety of systems that will include a suitably sized pressure regulator to ensure you’re operating as efficiently as possible.
Follow these 6 steps and make sure you get the most out of your compressed air system!
