md21722
Well-known member
Hi All,
I have a couple of air compressors I've combined in parallel to build CFM delivery. I've done some computations and don't understand the outcome.
Compressors:
Jenny K2A-8P - 2HP single stage with an 8 gallon tank, 1140RPM pump, rated 8 CFM @ 125PSI dated 2003
Emglo K2E-30 - 2HP single stage with a 30 gallon tank, 1140RPM pump, rated 8 CFM @ 128PSI dated 1995
Champion RE-7 - 2HP dual stage with a 60 gallon tank, 675 RPM pump, unknown rating, dated 1955
Piping:
All compressors have 25-35 feet of hose between them and the manifold that connects them together.
In total its 98 gallons of tank.
Extra information:
I live at 6,500 feet where air compressors, generators, and basically anything that ***** in air and is naturally aspirated is downrated about 20% due to altitude.
Tests:
If I use only the Jenny K2A-8P to fill both its 8 gallon tank and the 60 gallon tank, 68 gallons total, it takes 3 minutes 48 seconds to fill from 100-130. Normalized to a 30 gallon tank, this is an effective rate of 3.26 seconds/psi.
If I use only the Emglo K2E-30 to fill all three tanks, 98 gallons total, it takes 5 minutes to fill from 100-130. Normalized to a 30 gallon tank, this is an effective fill rate of 3.33 seconds/psi.
If I use only the Emglo KE2-30 to fill only its own 30 gallon tank, it takes 129 seconds to fill from 100-130. This is an effective rate of 2.83 seconds/psi.
If I use both the Jenny K2A-8P and Emglo K2E-30 to fill all three tanks, 98 gallons total, it takes just 2 minutes for an effective fill rate of 1.22 seconds/psi normalized to a 30 gallon tank. I would have expected a fill rate of 1.65 seconds/psi, but am getting about 30% faster.
If I use only the Champion RE-7 to fill its own 60 gallon tank from 100-130 psi, it takes 5 minutes. Normalized to a 30 gallon tank, it's an effective fill rate of 5 seconds/psi.
Then if I add in the old Champion RE-7 to the Jenny K2A-8P and Emglo K2E-30, to fill all three tanks from 100-130 psi, 98 gallons total, it takes 1:15 for an effective fill rate of 0.77 seconds/psi normalized to a 30 gallon tank.
At the time of all tests, all pumps were already running, producing air, so pressure switch cut in and cut out would not apply.
So it appears that the compressors "slow down" when pumping up extra tanks, but when they all work together, their sum is greater than the parts. I don't understand why this is occurring. I can only guess that less run time generates less heat, hot air, etc. and so for that reason they "gain" some efficiency.
However, if I run them all operating the air hog grinders, I'm at a fairly consistent run time. For example, I can run the grinder 60-75 seconds, wait 60-75 seconds for air pressure to build back up, and can do this repeatedly. By then the air compressors would all be warm or hot. The Jenny/Emglo discharge temperature is around 180-200F. The Champion is around 125-130F. The temperatures seem fairly normal for single vs dual stage and pump speeds.
Any thoughts?
I have a couple of air compressors I've combined in parallel to build CFM delivery. I've done some computations and don't understand the outcome.
Compressors:
Jenny K2A-8P - 2HP single stage with an 8 gallon tank, 1140RPM pump, rated 8 CFM @ 125PSI dated 2003
Emglo K2E-30 - 2HP single stage with a 30 gallon tank, 1140RPM pump, rated 8 CFM @ 128PSI dated 1995
Champion RE-7 - 2HP dual stage with a 60 gallon tank, 675 RPM pump, unknown rating, dated 1955
Piping:
All compressors have 25-35 feet of hose between them and the manifold that connects them together.
In total its 98 gallons of tank.
Extra information:
I live at 6,500 feet where air compressors, generators, and basically anything that ***** in air and is naturally aspirated is downrated about 20% due to altitude.
Tests:
If I use only the Jenny K2A-8P to fill both its 8 gallon tank and the 60 gallon tank, 68 gallons total, it takes 3 minutes 48 seconds to fill from 100-130. Normalized to a 30 gallon tank, this is an effective rate of 3.26 seconds/psi.
If I use only the Emglo K2E-30 to fill all three tanks, 98 gallons total, it takes 5 minutes to fill from 100-130. Normalized to a 30 gallon tank, this is an effective fill rate of 3.33 seconds/psi.
If I use only the Emglo KE2-30 to fill only its own 30 gallon tank, it takes 129 seconds to fill from 100-130. This is an effective rate of 2.83 seconds/psi.
If I use both the Jenny K2A-8P and Emglo K2E-30 to fill all three tanks, 98 gallons total, it takes just 2 minutes for an effective fill rate of 1.22 seconds/psi normalized to a 30 gallon tank. I would have expected a fill rate of 1.65 seconds/psi, but am getting about 30% faster.
If I use only the Champion RE-7 to fill its own 60 gallon tank from 100-130 psi, it takes 5 minutes. Normalized to a 30 gallon tank, it's an effective fill rate of 5 seconds/psi.
Then if I add in the old Champion RE-7 to the Jenny K2A-8P and Emglo K2E-30, to fill all three tanks from 100-130 psi, 98 gallons total, it takes 1:15 for an effective fill rate of 0.77 seconds/psi normalized to a 30 gallon tank.
At the time of all tests, all pumps were already running, producing air, so pressure switch cut in and cut out would not apply.
So it appears that the compressors "slow down" when pumping up extra tanks, but when they all work together, their sum is greater than the parts. I don't understand why this is occurring. I can only guess that less run time generates less heat, hot air, etc. and so for that reason they "gain" some efficiency.
However, if I run them all operating the air hog grinders, I'm at a fairly consistent run time. For example, I can run the grinder 60-75 seconds, wait 60-75 seconds for air pressure to build back up, and can do this repeatedly. By then the air compressors would all be warm or hot. The Jenny/Emglo discharge temperature is around 180-200F. The Champion is around 125-130F. The temperatures seem fairly normal for single vs dual stage and pump speeds.
Any thoughts?
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