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jimff
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I have an air compressor rated for 3.7 cfm @ 90 psi. what would the cfm be @ 40 psi? Is there a simple formula I can use?
jimff said:I have an air compressor rated for 3.7 cfm @ 90 psi. what would the cfm be @ 40 psi? Is there a simple formula I can use?
Hi Ron. I understand your interpretation, but that's not what is typically meant for the small air compressor market (or even fairly large air compressors). When manufacturers talk about CFM, they aren't referring to the CFM at 90 psi which is what I believe you're suggesting. They're referring to "free air flow" as it's sometimes called. That's basically just the actual displacement of the machine. If they quote the CFM at a higher pressure, the machine will generally have a higher flow at lower pressure, but that has to do with gas that's re-expanding and leakage past piston rings. For a machine with a free air flow of 3.7 CFM at 90 psig, it may increase to 4 or slightly more CFM at 40 psig, but that's because the machine loses capacity due to leakage and recycle (void volume) as discharge pressure is increased.RonL said:Guess we said the same thing in different ways, so a free flow of air at no compression, will be 22.65 cfm at whatever rpm the 3.7 cfm@ 90 psi was taken.
CFM is actual. The compressor actually displaces X CFM, so you have to determine SCFM by comparing to actual conditions. If the temperature and pressure of the air being drawn into the compressor is at standard conditions, then the compressor is compressing that amount of air in SCFM. So for the 3.7 CFM compressor taken as the example, if the air going into the compressor is at standard conditions the flow is 3.7 SCFM. So it doesn't matter what the discharge pressure is; if the inlet conditions are standard, the flow in CFM is also SCFM.Jobrag said:Is the cfm value taken as actual or standard?
The formula for calculating CFM (cubic feet per minute) at a different pressure is: CFM₂ = CFM₁ x (P₁/P₂) x (T₂/T₁), where CFM₁ is the initial CFM, P₁ is the initial pressure, T₁ is the initial temperature, P₂ is the new pressure, and T₂ is the new temperature. In this case, we can plug in the given values to get: CFM at 40 psi = 3.7 CFM x (90 psi/40 psi) x (520°R/530°R) = 8.4 CFM.
CFM at 90 psi refers to the amount of air that can be delivered in one minute at a pressure of 90 pounds per square inch. It is a measure of the air compressor's output and is used to determine the appropriate tools and equipment that can be powered by the compressor.
As pressure increases, the volume of air decreases. This means that at a higher pressure, less air is able to flow through a given space in a given amount of time. This is why CFM decreases as pressure increases.
Yes, CFM can be converted to other units of air flow, such as liters per minute or cubic meters per hour. However, it is important to note that the conversion factor will depend on the pressure and temperature at which the CFM value was measured.
The CFM requirements for tools and equipment can usually be found in the manufacturer's manual or specifications. If this information is not available, you can estimate the CFM requirements by looking at the tool's air consumption rate and multiplying it by the number of tools being used simultaneously. It is always recommended to have a higher CFM compressor than the estimated requirement to ensure sufficient air flow.