# Air Compressor Pressure vs CFM vs SCFM

• Shariq Qazi
In summary, Russ_Watters and Mike_Phelps from PF provided helpful advice on the Compressed Air Calculations. They advised to make sure the quality of the compressed air is good, and to account for the temperature changes when doing the calculations.
Shariq Qazi
So my boss hook me up with the Compressed Air Calculations which we never did previously at our workplace.
So started researching about the subject and designed a Compressed air system.
The only thing i am not sure about now here is the relation between CFM vs SCFM vs Pressure.

Let us take an Example:
An Air compressor of 250 CFM @ 8 bar(FAD) pressure outlet roughly translates to 2114.93 SCFM at 30 deg Air Temp.

Now if i want the Air at 1 bar atmospheric pressure at the outlet for some reason, will i get 2114.93 CFM from the Compressor if we use PRV to reduce the pressure.

I used TLV toolbox for the Air Compressor Calculations.

Welcome to PF!

You didn't actually ask any questions there, but it looks like you discovered by accident that the "S" in SCFM stands for "Standard" (as in standard temperature and pressure). SCFM is useful because:
1. The inlet and outlet CFM of a compressor are different.
2. The pressure at which a compressor is rated affects the CFM but not (necessarily) the SCFM. So using SCFM makes it easier to compare different compressors.

Shariq Qazi
russ_watters said:
Welcome to PF!

You didn't actually ask any questions there, but it looks like you discovered by accident that the "S" in SCFM stands for "Standard" (as in standard temperature and pressure). SCFM is useful because:
1. The inlet and outlet CFM of a compressor are different.
2. The pressure at which a compressor is rated affects the CFM but not (necessarily) the SCFM. So using SCFM makes it easier to compare different compressors.

Thanks for the reply russ_watters.

The only thing that is giving me hard time here is will the air compressor give me 2114.93 CFM at the outlet if we use a PRV to reduce the pressure from 8 bar to 1 bar(a).
I mean to say will the CFM increase if we reduce the pressure at outlet

Shariq Qazi said:
I mean to say will the CFM increase if we reduce the pressure at outlet
Certainly: when you pressurize air, you reduce its volume and therefore when you de-pressurize air you are allowing it to expand and increase its volume.

An important caveat is that the air is treated as isothermal (constant temperature) in these problems, but the actual path the air takes does involve temperature changes. That may have to be taken into account depending on the specifics of your application.

Shariq Qazi
also adding to what Russ said ( he is always the top notch advisor here)
make sure the quality of the compressed air is what you want. If you have a high precision instrument the compressed air is running, and you have a lot of moisture in the air, you will have longevity problems. You may need an air dryer added to the system as well.

Shariq Qazi
Thank you so much Russ and Mike.
It was indeed very helpful.
I shall update you'll about my project when i complete the entire design.

## 1. What is the difference between air compressor pressure, CFM, and SCFM?

Air compressor pressure refers to the force at which the compressed air is delivered from the compressor. CFM (cubic feet per minute) is a measure of the volume of air that the compressor can deliver per minute. SCFM (standard cubic feet per minute) takes into account the temperature, humidity, and atmospheric pressure to provide a standardized measurement of the amount of air delivered.

## 2. How does air compressor pressure affect the performance of the compressor?

The higher the air compressor pressure, the greater the force at which the air is delivered. This can affect the performance of the compressor by allowing it to power tools and equipment that require a higher pressure, such as air hammers or sanders.

## 3. What is the relationship between CFM and SCFM?

CFM and SCFM are both measures of the volume of air delivered by an air compressor. However, SCFM takes into account the atmospheric conditions, while CFM does not. This means that a compressor with a higher SCFM rating will deliver more air at standard conditions than a compressor with the same CFM rating.

## 4. How does air compressor pressure and CFM affect the air tools being used?

The air compressor pressure and CFM can affect the performance of air tools in different ways. Higher pressure can provide more power for tools that require it, while a higher CFM will allow for longer usage of air tools before the compressor needs to refill. It is important to match the air compressor specifications to the requirements of the specific air tools being used.

## 5. Can an air compressor's pressure and CFM be adjusted?

Yes, many air compressors have the ability to adjust the pressure and CFM to meet the specific needs of the user. This can be done through the use of regulators and other control devices. However, it is important to note that adjusting the pressure and CFM can affect the performance and efficiency of the compressor, and should be done carefully.

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