Air Tank

[ste6168]

I know this is a bit of an open ended question, but how long would a 7 gallon air tank last when being used with a blow gun?

I occasionally have the need to take a compressor onto a boat, usually to try and blow out a mucked up condensing coil or condensate drain.

Anyway, saw the 7 gallon aluminum air tanks at Harbor Freight the other day and was thinking it would be significantly easier to haul that down the dock to a boat than a compressor, even a small one isn’t super light.

7 gallon Portable Aluminum Air Tank

Amazing deals on this 7Gal Aluminum Portable Air Tank at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

Thoughts?

 

[AA/FC]

A 7 gallon air tank at 125PSI (for example) would probably provide less than one minute of trigger time with a blow gun. Sure, it will take longer than 1 minute to completely drain the tank but the pressure will become so low that the blow gun becomes ineffective. A few quick bursts, fine..... anything longer than that, probably not what you're looking for.

Back in the 70's and 80's, and even in the 1990's when R-22 refrigerant was like $0.20 cents per pound, most A/C repair techs just used a blow gun on the end of an air hose connected to a 30 pound refrigerant tank to blow out dirty condensers and whatnot. The bonus was.... if you know how refrigerant works.... the tank would retain it's full pressure until that last ounce of refrigertant was finally gone...... not like a standard air tank that continually loses air pressure as the air is used. Unfortunately, this is not an option today with the price of refrigerant. lol.

 

[GeoBruin]

I can tell you with some certainty if you know:

- The pressure to which you intend to fill the tank
- The pressure to which you intend to regulate the airflow coming out of the tank
- The flow rate of your intended airgun at that regulated pressure
- The minimum flow rate you consider to be useful after the tank drops below the regulated pressure

But just using some approximate values:

7 gallons is almost 1 cubic foot (rounding up).

If the initial pressure is 160 psi, and the minimum desired working pressure is say, 50 psi, Boyle's Law tells us that's 3.2 cubic feet you will exhaust from the tank to reach 50 psi on the tank gauge.

Let's say your blow gun will flow 40 cfm at 50 psi. That's 40 cubic feet every 1 minute or .67 cubic feet every second. So how long to flow 3.2 cubic feet?

.08 minutes or about 4.8 seconds.

But maybe that's worst case scenario. Let's say your blow gun is actually useful at 30 psi, and your gun will only flow 20 cfm at that pressure. Now we need to exhaust 5.3 cubic feet from the tank to get it down to 30 psi. At 20 cubic feet per 1 minute (.34 cubic feet per second) it would take .265 minutes or 15.9 seconds to drain the tank down to 30 psi.


But keep in mind you will need to change out some fittings to be able to run a blow gun in the first place, and you would need a regulator (which does not come with the tank) in order to set any of the above parameters. Otherwise, you're just using the little brass valve that comes with it to adjust your flow rate, and the flow rate will vary with the pressure remaining in the tank.

I have that tank, and it's useful for lots of things, but you won't get a lot of useful run time with a blow gun.

 

[no704]

Use a 5lb co2 bottle.

 

[cvairwerks]

Unless you are using an unregulated blow gun, they’ve been throttled down to 30 psig max at the tip for lots of years now.

 

[Odd-job]

My 30g tank doesn't seem nearly enough before needing to turn the motor on

 

[seber]

As others have noted, it won't give you enough time to do much. On the other hand, a paint can full of air for blowing out keyboards lasts a fair amount of time. Can you make do with a much smaller nozzle?