Air Hose Loss

Hi, Don.

A couple things--and please have fun correcting my errors.

If you're dropping 1 psi at the compressor, wouldn't the calculation be airbrush psi/19 instead of 20?  That would give you only a 15.8% drop in static pressure instead of 20% (for the first airbrush you tested), and only represents a loss of about 0.3 cubic feet of air (insignificant?), taking into account all other factors as constant (see next paragraph).

Also, pressure by itself can't be accurately calculated without taking into account temperature, can it (remember pv=nrt)?  Loss, at least in ventilation studies, has to additionally factor in duct diameter, duct surface configuration (e.g. corrugated vs. smooth wall) humidity, and hose (duct) length, as well.

Edit:  This paragraph removed because the commenter is an idiot.

Edit:  This paragraph removed because the idiot isn't thinking clearly.

Have a blessed day,

Gip

Hi Gip,

Thanks for responding to my post.

I'm just sharing the results of my simple experiment.  The numbers came from the pressure gauge shown in the photo, and the only calculations were of the percent reduction in pressure when the trigger was depressed.  The main point I wanted to make is that the pressure at the airbrush is not the same as the pressure at the regulator, at least not in my case.  When someone says that they spray at 20 psi, you have to consider which air hose they have, how long it is, and which airbrush it's connected to.

Don

Don, what a great experiment!

This experiment points out why I never try to say "this is the correct PSI" or "this is the correct thinning ratio", as far too many variables can play havoc with such finite statements.

There can be significant loss in any pneumatic or hydraulic system, and it is one reason why I have a regulator mounted at my booth. I'm currently using a 6' braided hose with inline moisture trap, but have the 4' vinyl hose in my airbrush toolbox. As I have two moisture traps (one on the compressor, and one after the regulator), I think I may swap out the braided, and see if I can pickup a PSI or two! I've always used braided hoses as I was told that the vinyl had a tendency to lose pressure due to flex in the hose. Braided hoses resist that tendency, but perhaps the length equals that out? The vinyl is certainly lighter!

One thing I do is set the air pressure with the trigger open, so that my reading is, at the very least, not reading a false pressure. Once I set my regulator, I adjust pressure "off the model" until it is spraying in the manner I want, and I don't actually pay attention to the amount of change. Perhaps I should start keeping logs? Hmmm, must think about that...

Very interesting Don. I like your web site with all the great information.

Thanks for sharing.

George