Compressor/tank question

OK, let's see if we can make this work.....
A standard 20 lb. propane cylinder has OVERALL dimensions of 17.56" tall and a diameter of 12.16" . Therefore, the radius = 6.08" Since the formula for cylinder area is pi X radius squared X height, I get an area of 2,039 cubic inches. Divide that by 144 cubic inches per cubic foot and you get 14.16 cubic feet as the area. Now multiply the area by the working pressure, which I assume will be about 150 psi (the rating of the compressor) and dividing by standard pressure (14.7 psi at sea level), you should get 144.5 standard cubic feet. Now divide the standard cubic feet by the operating pressure of the airbrush (let's say 10 cfm for round numbers), and you get about 15 minutes of spray time from a standard 20 lb. propane tank.

Personally, I think I would look at other options....

Gip Winecoff

If you know anyone in the heating and cooling repair business the tanks that refrigerant comes in makes a good bottle. The places usually just throw them away (a friend of mine has a whole big pile of them outside his shop!). They are about the same size as a #20 propane tank I'd guess.

There are "Kits" that will convert them into tanks for filling tires, which basically have a manifold that connects to the tank, a filling valve, a pressure gauge, and a short hose. I think they cost around $20 or so. To that you would need to add a regulator (another $20) and a filter/dryer (another $20). Say around $60 to $75 total. You can also buy a tank at Sears with the hose, gauge, and filler already on it for around $30. You'd still need the regulator and filter/drier though.

Edit ..
I forgot, you'd also need a safety valve to release the pressure if it gets too high. That's included in the "Kits" but if you try and DIY you'll need one.

You might also want to look into a pressure switch. Hook your compressor to the tank through the pressure switch. When the tank pressure gets to the low set point it will turn on the compressor. When it gets to the high set point it turns it off. You'd have to do a little wiring, but that's basically all a "Normal" compressor is; a pump, tank, and pressure switch.

LOL...you made my head hurt! But thanks for breaking it down. I was looking for a compromise between a better compressor and going the canned air route.

You have both a tank and a compressor. It depends on how much painting you think you will be doing.

I think, for your average model, 15 minutes is more than enough time. And you just have to go outside to when the tank is low, vs going to the gas station for refills.

QUOTE: Say around $60 to $75 total.

It sounds like, for a few extra bucks I can just do it right and get a better compressor.

QUOTE: I think, for your average model, 15 minutes is more than enough time

The only problem is that of decreasing pressure. At some point, you're not going to get a full 10cfm (example) from your tank. The 15 minutes would include the time it took to take the tank down to standard pressure or essentially, zero.

I agree that you may find it more economical to invest a few extra bucks into an airbrush compressor.

Gip Winecoff

Yep. But ... to prevent a pulsating airflow you still need something with a tank on it. The tank acts as a buffer between the compressor pump and the outlet (airbrush in this case). If you hook a tool / airbrush / whatever directly to the compressor pump you'll get a shot of air on each pump stroke and then nothing on the intake stroke. The result is a pulsation of the airflow. When you use a tank the air is coming from the tank and the pump part just keeps the tank up to pressure.

I did see a post recently pertaining to airbrush compressors, and some of them reportedly don't plusate too badly. I don't remember what they were though.

I use a 6 gallon 2 hp shop compressor with my brush simply because it's what I had. The problem is that it is NOISY when it kicks on, and it always startles me and makes my hand twitch. I've got a couple of old refrigerant tanks and the kit to convert them to air tanks, just haven't had time to put it all together. One of these days I will just to get away from the noise.

Does anyone here use CO2 or Nitrogen tanks or tried them?
I have an airbrush compressor and a shop compresser (25 gallons), problem is my airbrush one is about 15-20 years old and noisy (but nowhere near worn out) and I dont want to add a bunch of stuff to my shop one. I have an Oxygen tank (cant remember the size but its about 2 feet tall) and at one time I was going to trade it in for a CO2 one (to cheap to pay 5 bucks a pop to fill my paintball tanks) but I had heard you could run airbrushes off them too. You see I work at night and on my days off I still run on night mode so if I decide to go out in the garage I dont want to make a lotta noise. I took the plunge this week and bought a double action airbrush, and I want to really get my moneys worth out of it.

QUOTE: Originally posted by cplchilly Does anyone here use CO2 or Nitrogen tanks or tried them?

I have been using a CO2 tank for nearly 10 years and I absolutely LOVE it!! There are many advantages to using one.

1. A CO2 tank has no motor and no moving parts to break. It is totally silent and VERY low maintenance.

2. CO2 is a completely dry gas. It does not require the use of a moisture trap, as does a compressor. Your paint job will never be ruined by condensing liquids.

3. CO2 is non-toxic and non-flammable.

I picked up my 20 lb tank and pressure regulator for $90. Since I own the tank, when I empty it, I can simply go trade it in for a full one for a nominal charge, probably less than $15. But I won't need to do this very often. I can paint literally dozens of kits with the CO2 in only one tank! It lasts seemingly forever!!

Make sure you get a regulator that shows the internal tank pressure and that allows you to manipulate the line pressure. The line range for mine goes from 0 lbs to 60 lbs; I usually work at 10 to 20 lbs.

Mark

Thanks for the info MEMEAU I have access to a lot of shop equipment and I can probably gets a discount on a flowmeter.

QUOTE: Originally posted by MusicCity Yep. But ... to prevent a pulsating airflow you still need something with a tank on it. The tank acts as a buffer between the compressor pump and the outlet (airbrush in this case). If you hook a tool / airbrush / whatever directly to the compressor pump you'll get a shot of air on each pump stroke and then nothing on the intake stroke. The result is a pulsation of the airflow. When you use a tank the air is coming from the tank and the pump part just keeps the tank up to pressure.

That is only true on a diaphragm compressor, not a piston compressor.

Mike

QUOTE: Originally posted by memeau QUOTE: Originally posted by cplchilly Does anyone here use CO2 or Nitrogen tanks or tried them? I have been using a CO2 tank for nearly 10 years and I absolutely LOVE it!! There are many advantages to using one.

Mark,

Do you ever have problems with the gauges freezing up if that CO2 is used for a long time? I know T-shirt artists who complain about that and I found out a trick to stop that from happening. Just set the CO2 cylinder into a 5 gal bucket of water and the gauges won't freeze anymore.

Mike

i took a refrigerator compressor from a used frig.(free of charge), took the compressor off of my cambell hausfeld, hooked the frig compressor to the existing tank components, bought $40 worth of items and i have a silent compressor. it works well for me. the items i bought were an air filter, a gauge, misc brass fittings, clear hose, check valve, a toggle switch, and a small moisture trap. no more annoying compressor noise! my wife and daughter went from to and i went !!!! see ya!

Saltydog, I'm picking your brain here. You've done the trick with the compressor that came to my head today. I have an 20 year old air brush compressor, Medea Whisper Jet II, that has a tank and is fairly quiet but has a oil-less motor. I thought about converting it to a silent compressor with a frig motor. All the other internal parts would remain the same. Did you use the heavy duty, plastic, translucent flexy tubing and plastic fittings like hardware store would sell to hook up the air supply lines?

i used the clear flexible refrigerator hose with 1/4 inch outside diameter. it was rated for 130 lbs so i figured it would work. it works beautifully. i used the brass nuts and compression fittings to attach the hose. the pressure switch on my old compressor cuts out at 100lbs and cuts in at 75 lbs. if i had a digital camera or scanner i would load it up and show it to you. i have a spare refrig motor i plan to build another silent com. using an old freon tank for my resevior. i just accumilating the parts and milling the various holes in the tank for now. the only thing ive found annoying about the frig com. is that it pumps its oil out into the clear lines so u definetly need a filter straight out of the compressor. youll have to drop some lubricant in from time to time. other than that, it works fine and is very quiet.

QUOTE: That is only true on a diaphragm compressor, not a piston compressor.

Absolutely correct, Mike. My mistake and I stand corrected. Thanks for pointing that out.

Couple of suggestions for what it is worth.

A. If you want to cut down on how many times the compressor cuts in during a session, you might consider adding to your storage capacity. For years I used one of the yellow oxygen tanks we removed from some C-54s. Right now I'm using a 40 gal airbrake reservoir from an old Ford semi. You should be able to find one in a junk yard for 10 or 15 bucks. I simply installed a T fitting in the tank, ran a line to one side of the T fitting, and draw air off the other side.

B. Put the aircompressor as far away from your working area as you possibly can. When we lived in a trailer, the compressor drove both my wife and me crazy. There was a storage shed at the rear of the trailer, so I put the compressor there, hooked up a remote switch in my model room and ran some airhose from the compressor thru the window to my room. A friend of mine simply put his compressor on the back patio during the spring, summer and fall. In the winter, he brought it inside to his room. He made a box out of 3/4 inch plywood which covered the compressor. The box set about a1/2" off the floor so he could get the air hose out and to let air get in. Was still noisy but much more livable.

Thanks guys for the info. I have the oil-less compressor ready to dissect and a factory made silent compressor for comparison so you’ve helped make this a do-able project. From what I can see the oil-less box is the same size as my oil-filled compressor and I’m assuming refrigerator motors are a standard size so it should all fit in the casing. And I’ll have to check into an oil filter or a someway to stop oil from ‘leaking’ out the motor. I also have the Osprey book called ‘Airbrush Painting Technique’ that shows an example of a home built refrigerator motor silent compressor. This is going to be a fun project.

Billy,

Refrigerator motors come in various sizes so you will have to find one that is about the same dimensions as your Silentaire has.
I usually see a few on Ebay and they sell for a good price.
I just saw this one on there:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2590268965&category=26261

Try and find one that is at least 1/6 or 1/4 hp as it will not have to run as long to fill the tank.

Saltydog,

Did you install an air filter on the inlet side of that refrigerator motor?
I have heard that if you don't they won't last as long as contaminants will destroy the motor in time.

Mike

Hey guys,
Add me to the list of happy fridge compressor users. Been going strong for 5+ years now with no complaints. Sounds like my setup is pretty similar to those already mentioned.

I'm going to 'rebuild' mine soon though. The fittings and stuff I used were pretty crappy, so I'd like to clean it up a bit with some clear tubing and nicer fittings. I also had some moisture (for the first time) in my line recently so I think my moisture trap is konking out. Time to replace that.

Murray

Check out this article from HyperScale...

http://www.clubhyper.com/reference/compressorgi_1.htm

Murray

Mike, thanks for the heads up on the refrigerator motor at Ebay. I was/is eyeballing that motor. The price looks very decent.

I think that refrigerator motor is too small.
It is only 65 watts which is only .08 hp.

This one might be better and is a little less than 3/4 hp if what I found from their web site is correct: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2591157180&category=42910

There are more on Ebay too. Just type in 'Refrigerator Compressor' and there are 7 of them.

Mike

Yeah, you're right. Even my Silentaire is 1/5 (.2) HP. If I built a compressor out of that small frig motor it would be out of breath all the time...pant...pant...pant. I gotta find a little larger. Ebay is the place to be. I'll have to try your search.

Saltydog,

Did you install an air filter on the inlet side of that refrigerator motor?
I have heard that if you don't they won't last as long as contaminants will destroy the motor in time.

Mike