How much more air? 4, 6 or 8 bar in a big tank

H

HajoD

Guest
Hi,

I' m airbrushing for a few years now, weathering model trains.


I have a technical question on air pressure and amount of air reserve available.

I am about to replace my cheap and loud membrane compressor with a silent oil cooled one.
Also i added last year a big 40 liter air tank from a truck. Big relief with respect to having constant air pressure...

This membrane compressor loads this big tank to 4 bar and kicks reloading at like 2 bar.

The silent compressor i can buy loads its little tank to 6 bar.
I will link this to my big tank as well.
Also, i can buy a bigger one that can load up to 8 bar.

(Of course airbrush runs at aprox 2 bar.)


My question now is: How much more air reserve i would get from the extra pressure?


Yes, the new compressors are silent, but still, will there be much more time between air loading with this pressure difference?

Hajo
Amsterdam, NL
 
My question now is: How much more air reserve i would get from the extra pressure?

Bit hard to understand what your asking, but if your doubling the pressure your pumping into your reserve say 8 bar, it should in theory double your supply. No doubt it wnt work exactly like that (No maths expert) but say if your air lasts you 20 minutes from your reserve at 4 bar, having twice the compression of air shld last you around 40 minutes, but if your compressors set at 8 bar and you use a bit, of course the compressor is going to try to replace it and run anyway. I assume you fill your reserve and then turn of your compressor? Because if not it won't really matter if you increase the input it can do and kinda removes the idea of a reserve, it will still prob take about the same time to fill it as a smaller one may to 4 bar, but it depends on how much it pumps out in comparrison to the other compressor, or how fast it can pump it, for example a twin piston over a single piston will fill that reserve prob in the same time at the higher pressure because its output is faster. Difference it what the compressor can do come down to, the air it can compress and how fast it can compress it..For example a 4 bar compressor and an 8 bar compressor may have the same top end, its the tank that may be thicker or able to hold more due to size, but sometimes there is a limit to its highest pressure due to the top end not being able to literally push more in due to its type, increase the piston size or the motor driving that piston and you can obviously then get higher pressures. My main compressor is just an ordinary workshop style but on the small end, 25 litre. It also pumps up to 8 bar (around 120 PSI), if I turn it off and paint it will last around 15-20 minutes (Pending of course on how much I use, ie background work, detail work etc), since your volume is twice that shld last you around 30-40 (Assuming no leaks in the system) before you may have to recharge, so if you bought something that went to 6 bar (About 80 PSI), prob half that before a recharge is needed so on and so forth..

Not sure if that answers ya question LOL
 
Some math then.

What you have now is something that loads to 4bar and you use it down to 2bar. So you have 4-2 usable before the compressor starts to refill.

Now if you pump to 6 bar you get 6-2 usable, i.e, double what you have now.

Pump to 8 bar you get 8-2 usable, i.e. Tripple what you have now between refills.

The size of your tank should be added to the above if you want to calculate volume of air, but as I understand it you will not change that, so I simplified a bit. For example, in your current setup you have (4-2)*40=200 liters of air to use before it will start to refill.

Which makes me think, a 10L 300bar scuba tank contains 3000L of air att sealevel. From that you could use (300-2)*10=2900L
 
Thats probably because there is an error in the math.

(4-2)*40=80 not 200

Better?
 
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