Low pressure airbrush compressors

crewchief227

Needle-chuck Ninja
Hey guys,

Been awhile since I've been around again. Well not too long cause I had that rant thread. Anyways, I was watching this guy's video
And besides the absurdity of having double shut off solenoids, no doubt why comments were disabled, this video brought up another point when he's timing how much "working pressure" he's getting before the compressor kicks on again. I didn't realize, cause I never really owned that many airbrush only compressors that ones like that Sparmax he's using only fill up to 60 p.s.i., compared to say my Silent-Aire 50-24 that cuts off around 120 p.s.i. Now for a minute let's pretend that both compressors have the same size tank, instead of the difference of 6 gal. Vs. 1 gal., at a reasonable 30 p.s.i. working pressure mine with double the main tank pressure would last so much more exponentially due to the total cubic foot of air volume squeezed in there.

Now I imagine the reason for the lower pressure in these 'cheaper' tanks is because of materials, and a weaker compressor head that can't push above this 60 p.s.i. limit. Which is a shame cause you would have so much more time before cycles. Cutting down on noise, heat, and line pulsation. So, I guess the lesson here is to pay attention to not just tank size, but also max pressure to determine how much working time a compressor will have.
 
The double pressure switches on these guys are really wierd.
I posted a thread for compressor calculations. http://airbrushforum.org/threads/compressor-fill-times-and-drain-times.20413/
Using the links in it you can figure out your fill times, actual cfm delivery over your pressure range, and your drain times.
For every 14.7 psi or so you can add the tank volume again as far as capacity goes. But keep in mind its really the range or difference in start to stop pressure that effects run time, rather than the max fill pressure, and those with higher fill pressure tend to have to do all their work against a higher load.

Part of the reason for the lower pressure is noise and size and cost of casing. They could use a smaller piston and have the cutoff at 120psi with the same size motor but it would be much noisier and run much longer than using a larger piston, unfortunately that motor cant constantly handle the load that its big size piston would be at 120 psi. Instead of going to a more costly capacitor start motor or a larger motor or more isolation or casing they simply cutoff at lower pressure and trade running more often for less noise and less running time when it is running.

Compare with the senco pc1010 which has a far more powerful motor that is actually a bit smaller, uses a far smaller piston and the pressure cutoff is 135psi, i think. It doesnt run quite as often but is a bit noisier, a bit more costly and the run times are actually pretty close to the same. Despite having a motor with 3 times the power and double the cfm delivery. Its fill range is 90-135 (45 range) instead being in a fill range from 40-60 (20 range). When comparing these the difference in range is only 20psi so given an average airbrush using .5cfm and a 1 gallon tank on both the time between cycles is only about 2 minutes longer on the senco since its really only taking advantage of the tank about one time again over the cheapo compressor even though its packed the tank four times over again.
Anyhow, its just a balancing act really.
 
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Yeah it is, but my point was really how these smaller "tanked" compressors can vary, and the extra cost for the more expensive ones is not just how quiet they are, or have better regulators, but a whole lot of 'unseen' components. And touting a compressors tank size doesn't mean much when it's only holding 60 p.s.i.
 
Yeah i mean, all in all your getting effectively double the tank size on something holding 120 and cycling from 80-120 instead of 40-60.
Its just not as huge of a difference in cycle time as I initially thought it might be because well, its still just a tiny tank.
But because the pressure is always sitting so far over what you regulate to, the actual working pressure stays much more consistent.
Instead of the huge swing in working pressure you see when trying to regulate from 40-60 down to 25.
You dont get much swing regulating 80-120 down to 25 when youre only throwing out .5cfm.
Thats why I use the senco all the time. Well that and 100% duty cycle means i dont ever have to care how much i use it.
 
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Oh and lets not forget a lot of cheapo compressors vastly inflate their numbers. Going by the same standards as the cheapos the senco would be 1hp at 2.4cfm or so. Reality is its like .5hp at 1.1cfm@40 and .7@90. You can generally cut the claimed ratings by almost half on the cheapies.
They do stupid things like rate cfm by how much it intakes instead of what it puts out at pressure, and rating the motors at peak which is stall hp
 
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