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Dual (two stage) refrigerator compressor?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Dual (two stage) refrigerator compressor?

Unread postAuthor: High-PSI » Fri Nov 25, 2011 1:28 pm

Hey Guys,

I just watched a video of a guy using a large air tank to feed a precharge of 60psi to a refrigerator compressor. With the precharge, the refrigerator compressor was capable of filling a large paintball tank (90 cu in) to 400 psi in less than a minute. So, I am thinking using two refrigerator compressors in series as a two stage pump may be the hot ticket to an innexpensive high pressure compressor.

Thoughts?

Matt
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 25, 2011 1:32 pm

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Unread postAuthor: High-PSI » Fri Nov 25, 2011 1:48 pm

Awesome.

Thanks, Man!

I am not looking for 1,800 psi, however. What I am looking for is 400 to 500 psi. Ideally I would love to see 1 gallon at 400 psi in 2 minutes or less. That may be asking a bit much, though. But, I also have a small 1/2 inch bore cannon that has a tiny tank. That thing would fill super quickly with a two stage refrigerator compressor.

I do appliance repair for a living. I can get parts really innexpsnsively. This should be easy and cheap to do.

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Unread postAuthor: al-xg » Fri Nov 25, 2011 1:53 pm

And in most cases you won't get 1800psi either.

I use a two stage setup and the compressor stalls at 1000psi. Some stage compressors will reach that on their own, really just depends on what you find.


Also you'll need a buffer tank between the compressors, ideally pressure regulated.

If you are just going for faster filling, compressors in parallel might be a simpler/cheaper/more effective solution.
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Unread postAuthor: High-PSI » Fri Nov 25, 2011 3:00 pm

OK, so the pressure between the compressors needs to be regulated and a buffer tank installed. Gotcha. That sounds reasonable.

So, what is the rate of fill (roughly) at a given PSI with these compressors?

Also, what about one of those tiny shop compressors ($69 Home Depot jobs) as a precharge compressor with the refrigerator compressor as a secondary? That would ease the build process, though it would be a lot louder.

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Unread postAuthor: High-PSI » Sun Nov 27, 2011 5:29 pm

Alright, after a bit of web searching, it looks like the refrigeration industry has a good option for a compressor tank as well. I have been looking at freon recovery tanks. Most of them are rated at 400 psi with a built-in relief valve set for 600 psi. That should make a perfect compressor tank! I have really been looking for a way to build an innexpensive (relatively speaking) compressor with a decent size pressure tank. It looks like twin refrigerator compressors, and a freon recovery tank along with the obvious regulators, fittings, and what-not will run me about $400 or so. That is half the cost of a prebuilt 400 psi compressor and would give me more than 400 psi if I had a need for it. Hmm, that saves me enough money to buy a good inverter to power the thing from the field.

This should be a good summer, next year!

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Unread postAuthor: warhead052 » Sun Nov 27, 2011 5:32 pm

Wait, really? I can charge my freon tank to 400 psi?! Wow! And there I was nearly shitting my self putting 200 psi into it.

I would say use the fridge compressors, that way you can also charge a small chambered gun to a higher pressure than 400 psi.
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Unread postAuthor: High-PSI » Sun Nov 27, 2011 5:45 pm

Make sure your freon tank is a recovery tank. I have not researched new freon tanks. I am not sure if the recovery tanks are different in that regard.

Just do a Google search for recovery tanks and see what is said. Nearly all of them that I ran across are 400 psi.

I like the idea of twin compressors for a number of reasons. For one thing, they can be paralelled or seriesed for higher pressure or higher volume. I could, also, setup the compressor to pressurize the main tank, and easily reconfigure the tank to feed the inlets of both compressors to have a high volume and high pressure compressor by using the prepressurized tank to feed the two paralelled compressors with a precharge. This should give very high output pressure at a fast rate.

In any event, I think this is the direction I will be moving in.

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Unread postAuthor: Technician1002 » Sun Nov 27, 2011 5:59 pm

Series works for water. Compressible gas changes volume when compressed. There is a reason a 2 stage 2 cylinder air compressor has one large cylinder and one small cylinder.,

Many 2 stage compressors are three cylinder like the one in this photo. Two cylinders in the first stage feed one second stage cylinder.

Note, two cylinders have intake air filters.
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Unread postAuthor: High-PSI » Sun Nov 27, 2011 6:09 pm

True, but two same sized compressors can feed into each other as long as there is an intermediate tank and regulator. Of course, that is complicated. I like the idea of prepressurizing the tank, then reconfigurating in to feed that prepressurized air (regulated to a reasonable pressure), into the two compressors as a precharge. That seems to be the easiest method of achieving high flow and high pressure. Of course, the only cannons I have that would need super high pressure have small tanks that do not need large volume to fill quickly.

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Unread postAuthor: warhead052 » Sun Nov 27, 2011 6:10 pm

High-PSI wrote:Make sure your freon tank is a recovery tank. I have not researched new freon tanks. I am not sure if the recovery tanks are different in that regard.

Just do a Google search for recovery tanks and see what is said. Nearly all of them that I ran across are 400 psi.


Oh its a recovery tank alright. 1 vapor and 1 liquid valve, and then the safety pop off on the back, plus the plug thing for computers, I removed that though and put my air hose in to that hole, which is 1/4" npt exactly.
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Unread postAuthor: High-PSI » Sun Nov 27, 2011 6:12 pm

warhead052 wrote:
High-PSI wrote:Make sure your freon tank is a recovery tank. I have not researched new freon tanks. I am not sure if the recovery tanks are different in that regard.

Just do a Google search for recovery tanks and see what is said. Nearly all of them that I ran across are 400 psi.


Oh its a recovery tank alright. 1 vapor and 1 liquid valve, and then the safety pop off on the back, plus the plug thing for computers, I removed that though and put my air hose in to that hole, which is 1/4" npt exactly.


Cool. You could, always, Google your specific tank if it has a label and make sure. If it has a pop-off, you can feel relatively safe.

Of course, that is "Use at your own risk". This is a lawsuit happy world we live in. :)

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Unread postAuthor: High-PSI » Thu Dec 01, 2011 2:30 pm

Hey Guys,

I wanted to say "Thanks" for the advice. I have figured out the ideal setup for my cannons. Much of this setup is due to the advice I was given here.

Here is what I have done;

I found a new in the box refrigerator compressor for $20. I bought some fittings and did a bit of experimentation and here is what I came up with;

I used my tiny 2 gallon shop compressor (tire inflator) and hooked it up as a first stage discharging into my refrigerator compressor as a second stage. Now, with one of my small cannons, I charged the tank to 300 psi using just the refrigerator compressor alone. That took close to 2 minutes. However, when I ran the primary compressor set for 60psi output into the refrigerator compressor, that same small cannon tank hit 400 psi in 11 seconds! I had to reach over QUICKLY to unplug the compressor because I was not ready for it to fill so quickly! I could not believe it. It went from 2 minutes to 300 psi, down to 11 seconds to hit 400 psi! Then I timed my 2 gallon tank fill on my 2 inch big cannon. With the refrigerator compressor alone, it tiook 7 minutes to hit 200 psi. However, with two stages, that time dropped down to a total of 2 minutes and 10 seconds! That time would have been much faster, but the primary tank was down to 0 psi once the cannon was charged to 100 psi. So, with a larger primary compressor, or a larger primary compressor storage tank, that time should be somewhere around 1 minute or so (maybe a touch longer).

At any rate, I am totally thrilled! I will weld together a cage for the two compressors, setup the regulators, safety equipment, and other odds and ends and have an ideal compressor for my cannons that should prove to last a long time. :)

Thanks again........

Matt
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Unread postAuthor: POLAND_SPUD » Thu Dec 01, 2011 5:52 pm

However, when I ran the primary compressor set for 60psi output into the refrigerator compressor, that same small cannon tank hit 400 psi in 11 seconds!
heh nice... the biggest issue is getting good large capacity high pressure tanks...

a scuba tank would be nice... just fill it once to 500 psi and then you don't have to turn the compressor on and off all the time[/quote]
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Unread postAuthor: High-PSI » Thu Dec 01, 2011 5:57 pm

True.

I am considering many different things. One good thing is, it looks like I can charge my big cannon in a minute and a half or so if I can get the primary stage to keep up with the secondary. It used to take 4 minutes to fill with my 12 volt air suspension compressors.

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