Oldvanman wrote:OK, so two compressors will work. What I have is a Porter Cable/20gal/8.3scfm@40/5.8scfm@90 I'm looking at a used Craftsman/33gal/8.6scfm@40/6.4scfm@90 for $225. It's a four
hour round trip to pick it up, no big deal. I can get a new
Bostitch/26gal/4.1@90scfm for $244 at WalMart. No specs for 40psi, not even on the
Bostitch home page. I guess one could assume about 6@40.

A commuter airliner was enroute from Warsaw to Krakow when the pilot pointed out the picturesque Vistula River on their left. Passengers stood up and leaned over to peer out the windows. A few minutes later, the pilot points out the snow topped Carpathian Mountains to their right. Again, passengers stood up and leaned over to gaze at the sight. The airliner immediately spun out of control, broke apart, and crashed to the ground. There were too many poles in the right half plane. Sorry, esoteric engineering joke from long ago.

You didn't take into account the air that would be added back in by the compressor, did you, or did I miss that? Seems to me in your scenario, you are only calculating how long the air already in the tank would last, disregarding the 5 or 6 CFM that would be added to it while it was bleeding down. Your formula should really be a constant plus a time dependent variable, i.e., at some time after squeezing the trigger, the pressure and volume would drop below what the spray gun requires. If this time is is less than the time needed to do a coat on a hood or a door, then there could be problems, but choosing the right reducer would buy some time to allow the compressor to catch up.

Based on my experience, without doing LaPlace transforms and stuff, I think I could spray individual doors or a hood before it petered out.

1MechEng wrote:

A commuter airliner was enroute from Warsaw to Krakow when the pilot pointed out the picturesque Vistula River on their left. Passengers stood up and leaned over to peer out the windows. A few minutes later, the pilot points out the snow topped Carpathian Mountains to their right. Again, passengers stood up and leaned over to gaze at the sight. The airliner immediately spun out of control, broke apart, and crashed to the ground. There were too many poles in the right half plane. Sorry, esoteric engineering joke from long ago.

LOL!

You didn't take into account the air that would be added back in by the compressor, did you, or did I miss that? Seems to me in your scenario, you are only calculating how long the air already in the tank would last, disregarding the 5 or 6 CFM that would be added to it while it was bleeding down. Your formula should really be a constant plus a time dependent variable, i.e., at some time after squeezing the trigger, the pressure and volume would drop below what the spray gun requires. If this time is is less than the time needed to do a coat on a hood or a door, then there could be problems, but choosing the right reducer would buy some time to allow the compressor to catch up.

Correct. I was only calculating how much spraying time would be added by hooking up each additional tank.

Based on my experience, without doing LaPlace transforms and stuff, I think I could spray individual doors or a hood before it petered out.

Well played! Not sure LaPlace transforms are the ticket here, as they are most commonly used in Electrical Engineering, but you certainly get bonus points for the obscure mathematical reference!!!