Air Tools and SCFM ratings

Feb 11, 2008

Air Tools & SCFM Ratings
by: Bill - Publisher

Kenan:

You need 5.7 CFM @ 40 PSI to run your spray gun, but the compressor only puts out 3.5 CFM @ 40 PSI.

So, if you are trying to run your spray gun continuously, without stopping, then very quickly the discharge pressure from your compressor will start to drop, and ultimately, you will not have enough air to paint.

The secret here is to understand how compressor output capacity, compressed air consumption, and receiver capacity interface.

You don't indicate what size of tank came with your compressor, but it's size will have a bearing on the whole scenario.

The compressor has a low pressure set point (the point at which the compressor auto-starts, and it has a high pressure set point too (the pressure at which the compressor stops compressing air).

Your receiver will continue accepting air from the compressor pump until the high pressure point is reached, and the compressor stops pumping air into the tank. That high pressure point is likely 100-120 PSI.

You now have a tank with a certain volume of compressed air at 100-120 PSI, and you either have your air discharge regulator set for the 40 PSI that your device needs or you have a regulator at your gun set to the required 40 PSI.

When you start using your spray gun, air will flow from the tank, through the regulator to your gun, but the compressor won't start again until the low pressure cut-in pressure level in the tank is reached, as the tank drains down from 100-120 PSI to the cut-in pressure point.

When that level is reached, and it's probably in the 60-80 PSI range, your compressor will start compressing air.

Your spray gun, however, is still getting air at 40 PSI as that's where the regulator is set, and the air in the tank is still higher than that pressure. Air at the required pressure will still flow to your gun.

Since spray guns chew up a lot of air it won't be long then before the pressure in your tank falls below the cut-in pressure, and even though the compressor is still running, your demand is now exceeding the ability of the compressor to supply and the air pressure in your tank will continue to drop.

If you continue using your gun at this point your air supply pressure will continue to fall, your painting will suffer, and your compressor will continue to run continuously.

If you plan your painting project to balance these issues, you can use a spray gun that far exceeds the supply capacity of a compressor.

Simply stop painting often enough for the compressor to catch up and fill the tank to pressure cut off, and then have time to cool down. The compressor has a duty cycle. It's worth understanding.

Hope this helps.

Cheers,

Bill

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Feb 11, 2008
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Submitted by: Bill - Publisher

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Kenan: You need 5.7 CFM @ 40 PSI to run your spray gun, but the compressor only puts out 3.5 CFM @ 40 PSI. So, if you are trying to run your spray gun continuously, without stopping, then very quickly the discharge pressure from your compressor will start to drop, and ultimately, you will not have enough air to paint. The secret here is to understand how compressor output capacity, compressed air consumption, and receiver capacity interface. You don't indicate what size of tank came with your compressor, but it's size will have a bearing on the whole scenario. The compressor has a low pressure set point (the point at which the compressor auto-starts, and it has a high pressure set point too (the pressure at which the compressor stops compressing air). Your receiver will continue accepting air from the compressor pump until the high pressure point is reached, and the compressor stops pumping air into the tank. That high pressure point is likely 100-120 PSI. You now have a tank with a certain volume of compressed air at 100-120 PSI, and you either have your air discharge regulator set for the 40 PSI that your device needs or you have a regulator at your gun set to the required 40 PSI. When you start using your spray gun, air will flow from the tank, through the regulator to your gun, but the compressor won't start again until the low pressure cut-in pressure level in the tank is reached, as the tank drains down from 100-120 PSI to the cut-in pressure point. When that level is reached, and it's probably in the 60-80 PSI range, your compressor will start compressing air. Your spray gun, however, is still getting air at 40 PSI as that's where the regulator is set, and the air in the tank is still higher than that pressure. Air at the required pressure will still flow to your gun. Since spray guns chew up a lot of air it won't be long then before the pressure in your tank falls below the cut-in pressure, and even though the compressor is still running, your demand is now exceeding the ability of the compressor to supply and the air pressure in your tank will continue to drop. If you continue using your gun at this point your air supply pressure will continue to fall, your painting will suffer, and your compressor will continue to run continuously. If you plan your painting project to balance these issues, you can use a spray gun that far exceeds the supply capacity of a compressor. Simply stop painting often enough for the compressor to catch up and fill the tank to pressure cut off, and then have time to cool down. The compressor has a <a target=Ã¢â‚¬ÂblankÃ¢â‚¬Â href="http://www.about-air-compressors.com/dutycycle.html"> duty cycle. It's worth understanding.</a> Hope this helps. Cheers, Bill

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