Compressor capacity for HVLP

[ChrisU]

Hi,
I'm fairly new to spray painting, after a few attempts have had some good successes with an HVLP gun and 2k paint. I have been looking into compressor capacity a bit, because there is a lot of information (misleading or otherwise out there). My question is this:

- The air flow required for my spray gun is max 300l/min at 4 barg.
Converting to normal litres/min, this means the air requirement is 1500nl/min

- The (small) air compressor has a FAD of 160l/min at 8barg
Again converting to nl/min, this gives 1440nl/min

Ok, so comparing the nl/min the small air compressor is close to the required capacity, but not close enough, especially if you want a good 'safety' margin, for example 50%.

In order to correctly compare air flow requirement with air flow capacity shouldn't all calculations be done in nl/min to avoid any confusion? I see a lot of text with people citing for exampe ' 12cfm required for spray gun, so find a compressor that matches 12cfm' but this takes no account for the HVLP gun using a lower pressure than the compressor's FAD quoted value.

Please correct me if I'm wrong! I have probably overlooked the obvious...

 

[Daz1968]

I don't think the pressure is a factor in calculating air use, the pump has a bore and stroke that equates to an amount it can theoretically pump, if this is 190 litres per minute then that's all it will pump, it will pimp this until tank is at pressure, the spraygun will take 300 litres of air per minute until pressure of tank drops to cut in pressure and once this is reached the pump cannot keep up with the spraygun.

 

[cju198]

You're right, but the bore and stroke gives a specific compression ratio, for example for 8barg, the compression ratio is approx 8:1 (maybe slightly more to account for losses). Therefore the 190l/min is the outlet volumetric flow condition, whereas the inlet volumetric flow is 8x 190 =1520l/min. Whereas mass flow is constant, it's just the air density that changes.