I have a five gallon tank I fill for my airbrush sessions. I usually fill it at approx. 110 lbs. pressure it hold a max of 135 psi. My question is why doesn't it last very long. I spray at 12-15 psi. . How do I get more time out of it. I usually get about 15-18 min. Can someone please explain?

I'm not sure what you're asking. You have a 5 gallon container filled with air at 110 psi. As you use air, the internal pressure falls inside the pump. Once it closes in on the max air pressure you're airbrushing at, there's no motivation for the air to go from the tank to your airbrush.

If you want your air to last longer, you have some options...

1. Use a bigger tank
2. Use a 2nd tank and connect them
3. Make sure you don't have any leaks
4. Fill your tank to a higher pressure
5. Buy a compressor/tank combo
6. Buy/rent a bottle of compressed air (think scuba type), since they run at much higher internal pressures, which means they have a LOT more air.

Richard:

Your 5 gallon tank at 105 psi holds 7 atmospheres of pressure (15 psi is about 1.0 atm): As you are working at 12 - 15 psi, you effectively have about 6 atm of pressure to work with (assuming for this that you stop spraying when pressure drops to or below, say, 10 psi). The volume of air you have available to shoot at your desired 15 psi = ( (105 - 15) / 15) x 5 gallons, or 6 atm x 5 = 30 gallons. Not a whole lot of working volume at your desired pressure! But quite reasonable for maybe 15 - 18 mins of AB time. IF, for example, you wanted instead to shoot at 30 psi (2 atm), you would use air twice as fast and get 1/2 the time...

When you read about folks using "tank air" for their airbrushing, generally they are either using a much higher pressure "compressed gas" cylinder at something between 1500 and maybe over 3800 psi (as in a compressed CO2 or Nitrogen tank or a SCUBA air tank), or they are running something like a large-tank "shop compressor" at about the same psi (ca 110 - 125) you are using - but attached to a "low-pressure" compressor which refills that tank when things get down to whatever cut-off pressure one sets the fill-regulator for.

Those who use the high-pressure cylinders get much more gas into their tanks (15 - 30+ x as much per "gallon" of tank volume) and thus much longer work-times per fill - but need to have high-pressure stage regulators, and (unless they own the correct compressor) need to get their tanks filled at a welding-gas shop or SCUBA shop which has such compressor, or bulk high-pressure gas. Those with shop compressors (like me) may have 10 or 20-gal tanks running at your ca 105 - 125 range, which gives us maybe up to an hour of actual AB time, and eventually the compressor kicks on and refills it.

Jesse identified your general solutions. I prefer the "shop compressor" route, but they ARE rather noisy for in-the-house use... I would suggest that, IF you decide to go with high-pressure gases, do NOT use pure Oxygen for spraying - BOOM!, and IF using CO2, vent this out if you do much work in a small closet or space - this poses no fire-hazard, but it IS notoriously non-life-supporting! High-pressure air is great for AB use!

Bob

Thank you Bob. That is the kind of reply that makes sense. I admit I do not fully understand the Math at first glance, but it suggests I move to a compressor just for my AB sessions. Thanks again.

Richard:

OK. If you are thinking going to a compressor - many folks have found a really good tank + compressor set up for cheap over at the Harbor Freight store (at least 3 of the local club members use these down here in Lafayette LA, for whatever THAT may be worth! LoL) - take a look around some threads on painting, airbrushes, compressors posted here and on other sites (FSM, TL, M-L, etc.) and you will find all manner of advice and info on what folks like and use, where to get them, etc.

MY summary of these: You will see discussion of AB-specific compressors both with and without built-on tanks (all of these things are generally small - 1/2 to maybe 2 gal if a tank - and usually quiet - usually run low pressures up to maybe 60 psi - made to be used in the house, and can cost from under 100 to several 100s), larger "shop compressors" (variably noisy - to - loud, tanks from 3 to 50 + gals, run at 100 - 125 psi - more versatile IF you run air tools, etc.), and the range of high-pressure tank options. Read on this stuff with an eye to what matters to YOU - cost? ease of use? safety? availability? noise and size factors? other uses? It will be most informative and probably interesting!

Good Luck, Choose "wisely", and ENJOY!

Bob

Here's the Harbor Freight 3 gallon compressor. I own one and love it. With a coupon you can get it for $39.99! Once the tank fills, I shut it off and can airbrush an entire cup of paint on the 3 gallons in total silence. Perfection!