eas compressor cfm??
- Thread starter zen
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fett
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10l , lol weeny
And here's the datasheet for the 315 line of compressors:
http://www.cfpwarehouse.com/thomas/compressors/pump_data/315cdc45.pdf
http://www.cfpwarehouse.com/thomas/compressors/pump_data/315cdc45.pdf
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The Wammers Calcs are a good average/time flow, as it takes into account the Volume Flow fall off as the pressure increases over a given time....
The specs in the attached pdf in a previous post, show the reduced Volume Flow at given pressures.
The specs in the attached pdf in a previous post, show the reduced Volume Flow at given pressures.
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The combined Gas Laws (P1V1/T1 = P2V2/T2) state that as the pressure increases the volume would reduce....
Hence why I said, Wammers answer of filling a 10 litre tank to 140psi in 5/6 minutes gives a good average over the entire filling range...
i.e.
At the beginning of the cycle the Volume flow is greatest and during the fill, the pressure increases, thus the Volume Flow reduces over time....hence the Wammer's quick calc is a good average.
The spec sheet attached gives different flow rates at the various differential pressures...and I was just pointing out that just because the eventual pressure is 140psi, don't read the Volume Flow Rate just for 140psi....it needs to be averaged over the entire fill range...again, why I agreed that the Wammers average was pretty sound.
Hence why I said, Wammers answer of filling a 10 litre tank to 140psi in 5/6 minutes gives a good average over the entire filling range...
i.e.
At the beginning of the cycle the Volume flow is greatest and during the fill, the pressure increases, thus the Volume Flow reduces over time....hence the Wammer's quick calc is a good average.
The spec sheet attached gives different flow rates at the various differential pressures...and I was just pointing out that just because the eventual pressure is 140psi, don't read the Volume Flow Rate just for 140psi....it needs to be averaged over the entire fill range...again, why I agreed that the Wammers average was pretty sound.
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CFM is a measure for volume units pumped with the source at 1atm. Wammers' numbers would be right if the intake was at 140psi
No that is not correct. Volumetric output decreases as pressure increases. The figure quoted is the average output of the compressor whilst filling a 10 litre tank in six minutes. Compressor volumetric output is usually quoted in free air movement. A 1 cu ft per minute compressor can displace 1 cu ft of air per minute at ambient pressure. It cannot do that at 140 psi. So if it takes the compressor six minutes to fill a 10 litre, 0.353146 cu ft tank the figure quoted is the average air flow from the compressor from zero to 140psi. If the intake was at 140 psi you would not need the compressor. Air would just flow through it to fill the tank.
Just seen that you beat me to it Saint.
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Jinx....
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I just added a bit to my post. Interested to know why you would need a compressor, if the inlet pressure was 140 psi.:doh::doh:
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Very true, but we would all need our own personal pressure chambers to stop us from imploding though....
The only reason I can imagine needing 140psi at the intake is for wammers math to be correct,lol. Your numbers are off because 10lt at 140psi is not the same, in mass, as 10lt at 1atm. So, just converting the tank capacity into cf and dividing it by a measure of time is not correct. You need to convert that (10lt@140psi) into the right volume at 1atm and THEN divide it by the time it takes to fill the tank.
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Ok if that's what you say. But Saint designs jet engines and he agrees with me, so i am happy. He designs aeroplanes i used to put them together. If it takes 6 mins to inflate a 10 litre tank to 140 psi. All you do is divide the capacity of the tank by the time taken to fill it, that gives you the average output of the compressor over the 6 minute period.
Irishrover
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As with any pump with a fixed displacement, i.e. fixed stoke and bore, as pressure increases the flow will decrease. Compressors and hydraulic pumps are rated at L/min or cu.ins. or feet/min at a given pressure, say 100 p.s.i. (6bar) or in the case of hydraulics, say 4100 psi (315 bar) upwards.
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Ditto....
And many thanks Wammers for your kind introduction....My Masters was in Aeronautical and Aerospace Design Engineering specialising in Gas Turbine Theory and Design.
I currently Design components for High Bypass Gas Turbines, so Thermofluids, Thermodynamics and CFD are high on my list of incredibly boring things to read....
Whilst your maths is correct, a 10 litre tank at pressure would hold more volume than the 'Water Capacity' at 1 atmosphere, Wammers example was based on capcity/time to average the flow rate and not capacity/flow which would average the time taken if the volume flow rate remained constant which it won't, as the volume flow will vary at a given pressure. (as per Irish Rovers example).
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Well, I'm a Civil Engineer by education and profession so I don't consider myself any less educated in simple thermodynamics.
When refering to a pump's CFM, unless clearly stated otherwise, this number is measured at atmosferic pressure. If you want to refer to it's CFM at other output pressure, you have to explicitly state it. X CFM @ Y PSI. Simple. Maintaining that this pump's output is of 0.05cfm while all the technical sheets show it to be around 20x higher is just beyond my understanding.
Just for giggles, try going into a compressor shop and ask for a 0.05cfm pump, capable of doing a max of 140psi. Then time how long that one will take to fill a 10lt tank...
When refering to a pump's CFM, unless clearly stated otherwise, this number is measured at atmosferic pressure. If you want to refer to it's CFM at other output pressure, you have to explicitly state it. X CFM @ Y PSI. Simple. Maintaining that this pump's output is of 0.05cfm while all the technical sheets show it to be around 20x higher is just beyond my understanding.
Just for giggles, try going into a compressor shop and ask for a 0.05cfm pump, capable of doing a max of 140psi. Then time how long that one will take to fill a 10lt tank...
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The only pump on the spec sheet that is capable of 150psi is the 315CDC56/12. Free air is given as .96 cu per min, and .35 cu ft per min at 140 psi. Unless Land rover use one of the smaller pumps over capacity. I have a spare one in the garage, if i can think on i'll measure the bore and stroke tomorrow. The only way to check your particular compressor, is to empty the tank, leave a door open, and time how long compressor runs before it switches off. Then do my sum. That will tell you average output.
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