Air Power

zekell,

Ya gotta love the arithmetic!

O.K., let's assume you have one (1) 1000 gal. LP tank, and that the LP tank has a volume of exactly 1000 gallons (I have no idea what their exact volume is, but we'll start, here).

The air sander you mentioned averages 4 cfm with pressures in the range of 60 to 90 psi gage. So let's do some more assuming: assume your LP tank is at 90 psi and 70 degrees Fahrenheit. You will use the air sander until the tank pressure is 60 psi, and we'll assume the temperature did not change. We will also assume the flow rate (4 cfm) is measured at atmospheric pressure (14.696 psi absolute) and 70 degrees F.

If you use air at 4 cfm, how long will it take to depressurize the tank from 90 to 60 psi?

You can calculate this in minutes by taking the difference in pressures (30 psi, in this case) times the volume of the tank in cubic feet (133.68 cubic feet) divided by the product of the atmospheric pressure (14.696 psi) and the volumetric flow rate (4 cfm).

If I didn't make a mistake, you could run your air sander for 1 hour 8.2 minutes.

Note: this tank is less than half the size of the one you dimensioned in a previous post.

So now what do you think?

River

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And they that use this world, as not abusing it: for the fashion of this world passeth away. (I Cor. 7:31)

So now what do you think?

River- Well, I think this is still fun, but its starting to hurt my head some.

OK,Your using a volume/pressure formula to fine out the actual working time down to the usable pressure level. That would be a more realistic idea. I'll trust your numbers scince its been a long time scince I burnt out at tensor calc, and lately had to be reminded of a volume formula by Unreg, (they did try to learn me better).

Your getting double the work time, thats great, but its still quite aways away from the 'coupla days of work I was hoping to get out of one tank.

Here, see what you can make of this :

http://www.pyramydair.com/cgi-bin/ac...ccessory_id=81

.50 cal big game hunting air rifles, hand pumps that can compress up to 3,000 psi ?

zekell,

I am no expert on pressure vessels, but I can imagine a large tank that could withstand 3000 psi would be an expensive proposition.

(I should add, my formula, above, may not be accurate at 3000 psi. I assumed air was an ideal gas, and I do not know if that is valid at that pressure.)

It is quite possible to pressurize an LP tank well past the 90 psi we were discussing. I am not sure of the pressure rating for a standard LP tank, but it must be well over 200 psi. It is not energy efficient to pressurize air to 200 psi, then drop it to 90 psi before using it in a tool, but if that is what you have to do...

River

__________________
And they that use this world, as not abusing it: for the fashion of this world passeth away. (I Cor. 7:31)

River- From what I saw the larger the tank the less pressure, smaller the tank the more pressure. We're starting to get into the 3,000 psi range and that means divers tanks an carbon composit tanks.

Similar to this system ;

http://auto.howstuffworks.com/air-car1.htm

These are expert types of systems beyond the means or expertise of most. Starting to crowd the fear level meter also. When I was not much bigger then a sand grub I watched a diving tank take off from the fill tank and fly right through a substantial cement wall. It was kinda exciting, I ran over and looked out the head sized hole it made in the wall, then looked back to the dive shop guys, and asked if they were going to go try and find it. They quietly looked at one another, then said, "no kid, we don't ever want to see that tank again."

Well, when this idea first tickled my fancies I thought I might've stumbled across a fairly cheap and clean way of storing a 'coupla days worth of energy.

Well, came up a day or so short. However it was an interesting and eye opening journey; Amish air power, people running most of their house on air, wind mill air compressors, compressed air bubbler well pumps, air powered cars, and ha, a compressed air big game hunting rifle, (and I wonder how fast you can pump that thing back up while being chased by a cape buffalo ?).

Well I'm stumped for now, but its too good a notion to just throw away, have to leave it on the back brain burner for now.

And I'd like to thank y'all for kicking the idea around.

Very interesting ideas! I can see how air power could be an alternate energy source for certain specific applications, but I don't see how you could run your home or homestead on air power without converting at least some of it to electricity, & there's the problem. I'm sure that you could improvise some kind of air powered electrical genarator, but I very much doubt that it would be practical unless you had some very cheap way to compress the air in the first place, & a very large storage tank. I think that all of the equipment involved would be much more expensive to buy & maintain than a straightfoward electrical set-up. You can run many kinds of power tools, & pumps, & other sorts of machinery off air power, but I haven't heard of an air-powered computer,TV,or vacume cleaner yet. Electricity is still the most efficient power source, so far.

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Freedom isn't Free

You'd have to use air as an alternative for long term storage of energy over batteries. Thst is only fesiable under 2 scenerio's 1 if the over loss conversion from compression and decompresion to generate elec. is less than the loss (including the self discharge) of batteries. or 2 you only use the elec generated from the air on a non regular basis like a summer cabin and you have a huge air tank that get's charged all year.

-- Tim

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