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Jul 27, 2012
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Brisbane - Australia
My Car
1973 Mustang Convertible
Hi to All,

Just wanted to pass on some good basic info on compressed air/ compressors/air tools in the hope my write up will help other Forum members into the future regards using and buying their gear and getting better outcomes for themselves.

When it comes to compressed air, air compressors and air tools, industrial or domestic, there is only one major thing that matters above all. AIR PRODUCTION AND AIR CONSUMPTION.

Let’s look at compressed air production first. What all compressors have in common is their ability to produce compressed air on demand. This can be broken down into two important things.

The volume of compressed air produced and the maximum pressure produced. There are a wide variety of all types of compressors that are manufactured to deliver various volumes and pressures of compressed air on demand. So firstly, to measure the amount of the volume of air a compressor can produce, time and cubic area were used as a yardstick of measurement of compressed air volume production. It goes as cubic feet/litres per minute.

Secondly, pressure produced by any compressor, is measured in PSI (pounds per square inch)/ BAR/ kPa. These three measurements I won’t go into as that is another topic all together on it’s own. The production of compressed air requires a lot of energy, be it electrical or gasoline. That being the case, we find that we can divide the compressor market into two categories. Domestic and industrial.

Domestic compressors usually run on mainly domestic power supplies of around 240volts and 10 amp circuits.(varies worldwide.) Industrial compressors usually use a three phase electrical power supply (415 volts)to run them and are capable of much greater production of compressed air amounts over single phased domestic air compressors. (you will usually find you can go up to a maximum 3 horse electrical motor on a typical 10 amp /240 volt domestic circuit) Some of these compressors are sold with a 15 amp plug, some are not, and sold with a 10amp plug. Try to avoid using long extension leads with any setup if you can, as they can produce voltage drop issues and burnt out motors.

So lastly, when we talk about compressed air production, there is only one thing that matters. FAD. What is FAD? FAD stands for free air delivery. So what is free air delivery? Free air delivery is the ability of any air compressor to deliver a unrestricted constant volume and pressure of compressed air with the drive motor and pistons in constant operation. Again, this is measured in cubic feet/ litres per minute plus the maximum amount of pressure that can be achieved in conjunction with that maximum volume output. So FAD spec or production, is your compressor going flat out or to the max in regards to what it can ultimately produce. So at the end of the day, FAD production is all there is and all that really matters. There ain’t no more air production on top of that FAD output.

However, in reality, all compressors are designed and manufactured not to have the motor or pistons running constantly. This is because of excessive heat build up in the motor and pistons, which will lead to premature wear and breakdown/failure. They are designed to run with motor and pistons stopping and starting at certain time intervals. This is also known as the duty cycle of a compressor. The duty cycle or run time of the motor and pistons is usually calibrated to a certain maximum pressure level (adjustable). Once the compressor reaches that designated maximum pressure setting the motor will auto switch off, and stop producing compressed air. This then gives the compressor a chance to rest and cool down a little before starting up again, producing more compressed air. This production or amount of compressed air produced on the duty run time cycle is again measured in cubic feet/ litres per minute. However, it is important to note, that the duty cycle spec on production of compressed air will be much higher than the FAD production spec. You should not purchase any compressor based on the duty cycle cfm spec, only the FAD spec.

In that regard, domestic compressor manufacturers mainly state the cfm spec based on the duty cycle specification, not the FAD spec. You tend to see the duty cycle spec in bold writing on the outside of the box packaging, and the FAD spec sometimes/ sometimes not printed in smaller writing mixed in with other compressor specs/ features quoted. This is essentially very misleading to the buying public, and many a purchaser has settled on buying the compressor based on the duty cycle production spec, and thinking the production capacity will meet their requirements, only to find out sadly that the compressor does not. The FAD spec should be the up front spec in bold large writing on the box cover, not the other way around.

So it stands to reason that when you are using or going to buy a new compressor, the FAD spec is the only spec to take into account, as that spec represents the maximum amount of compressed air your compressor can produce per minute, at any given running time. That leads us to the next big thing. AIR CONSUMPTION. There are a crazy variety of air tools out there today. They all have different amounts of compressed air volumes and pressures to make them operate properly.

This is called the air draw of any air tool. Air draws (volume and pressure) vary greatly depending on what air tool you are using. Air draw is measured in cubic feet/litres per minute and an operating pressure spec quoted.

Some air tools need great amounts of air volume and pressure to function properly. Some air tools need a high pressure and low volume of air to run properly. When using or purchasing any air tool, it’s important to verify the stated air draw of that specific tool. Why? Because your tool’s air draw should either be less or at worst, the same FAD spec your compressor has. If it’s more than your compressors FAD, then you will have problems. In my case, I got out of jail by buying a second compressor to my main one. I had to go the extra expense of beefing up the power point (15 amp double point),and running a dedicated new h/duty cable line/ 32 amp fuse on my meter box to cope with the extra amp./volts drain on my home system. ( now am running a 3 horse plus 2.5 horse teamed compressors). (My spray guns have an air draw around the 12 to 14 cfm spec).

For example, let’s say you have a spray gun with an air draw of 12 cubic feet per minute at around an operating pressure of 45psi.., but your compressor has an FAD spec of 10cubic feet per minute, then your compressor will not be able to keep up with the demand of compressed air needed to run that spray gun properly, even though your compressor is running constantly. You will experience noticeable pressure drop ( poor atomization) leading to running out of air.

So we learn the most important thing is to correctly marry up the air consumption of any air tool with the air production of any air compressor(in the FAD SPEC), domestic or industrial. In regards domestic compressors, we find that due to the limited domestic power supplies, there are limitations as to the maximum amounts of the volume of air that they can provide to the home jock. If you are using or running big air draw tools at home,(say around 12 to 18 cfm), you will find troubles as your compressor will have trouble keeping up the demand of compressed air that tool needs to function properly. Bottom line here is to use or purchase a single phase compressor with the maximum or biggest FAD spec you can find in the market place. Don’t forget the quality of the compressor as well for a longer owing life free of trouble. A constant hot, over run compressor with back to back runtimes on the duty cycle, that can't keep up with the larger amount of air consumption or air draw, will have a shorter life span.

Lastly, I want to make a point about compressor air tank capacities/sizes. Larger or secondary satellite tanks are a help with compressed air production or delivery. However, the concept is limited, as again, FAD is all that matters. For example again, let’s take our spray gun that has an air draw of 12 cfm and the compressor has an FAD of 10cfm. If you are running a bigger tank or tanks, then yes, your stored supply of compressed air will initially meet the demand of that gun, but when that stored air is depleted, you are then back to a FAD production of compressed air to carry on operating the tool. If the FAD is not enough for the demand of the gun, you will then start running out of compressed air needed to operate it properly. So running larger tanks helps, but won’t solve your air production problems. Again FAD of any compressor is the most important factor to consider.

Hope that helps,

Greg, :)
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very timely for me. Thank you. Working on setting up the new shop with compressed air supply lines. Any advice on how supply lines impact any of the multiple variables here? I have MaxAir 3/4 lines I am going to be running. The longest run will be in the 80-85 ft length from the back of the shop to the front. Thank you for this information and any other insights.
very timely for me. Thank you. Working on setting up the new shop with compressed air supply lines. Any advice on how supply lines impact any of the multiple variables here? I have MaxAir 3/4 lines I am going to be running. The longest run will be in the 80-85 ft length from the back of the shop to the front. Thank you for this information and any other
Hi bk,

Thanks for your reply. I can be of help to you regards setting up your new supply lines, but my answers will again be in basic form as my post above. Setting out a new workshop system is a big subject all on it's own.

Firstly, any air setup should comprise a design or layout of a main supply line or ring line. When setting up the main supply line it's very important to select the largest internal diameter pipe you can. The material can be metal or pvc air line or rigid plastic. Rigid plastic has become popular these days as you can buy all the necessary unions to go with the piping. When we talk about running length of the main supply pipe creating issues with long runs as adversed to pressure drop issues, we look at the physics. How it works is the smaller the internal diameter of your main supply pipe is, and the longer your run is, the more volume and pressure drop you will experience. So larger diameter pipes will allow more volume of air to pass through at any given time, allowing more pressure as well. You can go up to around the 2 inch or more internal diameter for great results here. When installing the main line , it helps to put a slight fall off level so any water in the main line can naturally drain back towards the compressor. The main line should be installed as high off the ground as possible. Your run of 80 feet or so is acceptable, but it would be better to go with a larger diameter main supply line pipe if you can.

If you are running mixed air tools, such as spray guns and air sanders, grinders nail guns etc, remember that the spray guns and fresh air supply to your hood, require the best cleanest, moisture/oil free air you can provide. The installation of air regulators is vital here. It's common to install 3 or 4 regs in a system to produce maximum moisture free results. I like to position mine with the first reg about 10 feet away from the compressor, The others, can be placed at random intervals down to the end of the main line. A main supply (ring line) has the line connecting back to itself to form one continuous line loop. This method is optional but not necessary. These regs can be drained or bled when moisture build up is noticed in the clear plastic bowls of the regs.

If you notice that you have a beige colored sludgy coating on inside of the reg bowl at any stage, then that spells big trouble, as it usually means that your compressor is allowing oil to escape from the pump and out into the tank and then into the air lines. Worn rings are usually the cause of this happening. Fouled air lines and regs contaminated with oil have to disposed of sadly, and the compressor itself will need major repairs and cleaning out at great cost. Air fed hoods will require their own special regs for the breathing in of clean filtered air.The other tools will require oiling as ongoing maintenance. You can manually oil them or set up a dedicated separate line with an auto oiler and moister reg installed on that line only.

Using the biggest dia supply line will enable you to take several branch lines off that main line to various parts of your workshop if so desired without loss of air delivery. Drain your compressor every day after use. Don't leave compressed air in your tank for long periods of time. (more than a day) When compressed air leaves the compressor, it will be heated up to varying degrees. As it passes down the main line it starts to cool down, thus causing moisture or water to form in the pipes due to condensation taking effect. A hot continuous run compressor will end up producing much more condensation than a cooler run compressor. I place shop fans trained on both my compressors motors and pumps to help cool them down. This is a trick that works very well all 'round. Work out what your maximum air consumption will be based on the air tools you will be using, and the number of persons potentially using air tools at the same time, as adversed to what maximum FAD PRODUCTION YOUR AIR COMPRESSOR CAN PRODUCE.

Hope that helps,

Greg. :)
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Hi rcadd,

Thanks for posting a new compressor you are wanting to buy.

I thought i would respond to your post and mention a few things that would be in your best interests.
I don't want to be a killjoy, but i would think twice before ending up buying this compressor. First up, the decision to start manufacturing scroll or screw type
compressors into the domestic home compressor market is an interesting concept. Industrial scroll type compressors have been around for a long time in the industrial arena and have delivered decent results in the market place. It should be known that these types of compressors have long duty cycle run times, and so they run quite hot. The industrial models are large capacity outputs, and so they require separate aftercooler/intercooler units (also known as filter/driers) to help cool down the excessive heat produced by them. Looking at the Eastwood ad, you can see this compressor has what looks like a small type of aftercooler or drier attached to the end of it.

How this would perform in managing to control the heat produced effectively, would be an unknown, and specs are not provided in this case. Secondly, when reading my post above, i make mention of compressor manufacturers or sellers, advertising/promoting, using misleading tactics to sell on their products. This ad is a classic example of that very thing.Why? Firstly, on the plus side, the ad heavily promotes how quiet this compressor runs. ( 63db) That's pretty good for a domestic compressor. But is that taken with a db reading 3 feet away from the machine, or 20feet from the machine? ( Warning - there is a disclaimer on the accuracy of that spec in small print). You would find it hard to match or beat that spec in the current marketplace if it's accurate. This feature has been heavily used and stated to promote the appeal of this machine to draw perspective buyers in.

However, on the minus side, misleading statements are made in the ad saying that it will handle most types of air tools is misleading and false. Secondly, it looks like it comes without an electrical plug, and so you will need to call out a liscensed electrician to install a dedicated power outlet/cable line/special dedicated fuse on the power board. It looks like it has a really big amp draw on motor start up and kick in, and thus needs a big heavy duty electrical setup to operate properly and safely. This will be an expensive extra cost on top of the big purchase price. I ended up paying around $600.00Au to upgrade my electrical setup as mentioned in my write up above.

But most importantly, it FAILS to state an FAD specification at all in the ad. This is misleading as the FAD spec is all that mainly matters when buying any compressor for home use. It claims to produce a (Powerful - 12.7 cfm @ 90 psi) Is that an FAD spec or a duty cycle spec?) Warning bells should be going off here, as to what will be the real compressed air output of this machine (who would know). By the way, 90 psi is not a good strong pressure spec for a compressor. Many air tools require greater pressures to operate properly. 120psi and upwards is the common pressure spec on most domestic compressors. As i have said, your best approach is to work out what air tools you will be going to use or run, and what will be the maximum air draw amongst of all those tools. Then select to buy a quality domestic compressor with the biggest FAD output that is on the market, and you can afford. Running quietness does play a part in choosing your compressor these days, but buying smart, and choosing the correct FAD output to meet your consumption/air draw needs is still the most important thing to take into account when buying and using your compressor.

So all up, this is a dodgy ad selling a compressor that has average and unknown real performance specifications, that is being heavily promoted on the strength of its running quietness. Buyer beware on this one! I'm sure you could buy better and smarter here, but that's your call at the end of the day.

Also, thanks very much to all you guys that have positively responded to my compressor write up. Glad you liked it, and hope you are now better informed!

Best of luck,

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A really great write up Greg. I think as most people, I wasn't even aware of fad. I've always assumed that the listed cfm@psi was the number that I had to be concerned about when it came to my air tools. Although I haven't run into any problems with mine, I don't run any tools that need a continuous air supply such as a spray gun. I'm for sure mine would fall short if I did. It's members like you taking your time and sharing your knowledge that makes this site so great.

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