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Two stage fridge compressor build

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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Unread postAuthor: High-PSI » Thu Mar 29, 2012 7:39 pm

Here are some pics.

The top cover is not on. But, other than that, it is totally finished.

Matt
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Unread postAuthor: Gun Freak » Thu Mar 29, 2012 7:52 pm

Good lord, high pressure parts galore!
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Unread postAuthor: warhead052 » Thu Mar 29, 2012 9:49 pm

Ahhh, I wish I had that. That's very nice! And the fact you reached 1,050 psi is even better.
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Unread postAuthor: jackssmirkingrevenge » Fri Mar 30, 2012 12:27 am

Truly fapworthy, great job!
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Unread postAuthor: High-PSI » Sat Mar 31, 2012 5:41 pm

I repaired the blown high pressure line and I did some more testing.

I setup my big 2 inch cannon with a 2 gallon tank and timed the fill. Now, as a baseline, keep in mind my previous compressor system (twin 12 volt truck airbag compressors) required 4 to 5 minutes to charge the tank to 250 psi depending on the state of charge of the car batteries I used to run them. With this new compressor, I tested the fill time in two ways;

{these tests were done with the on-board stage one pressure tank prepressurized to 200 psi prior to the tests. It takes about 4 minutes to charge that tank. However, the tank can be left to recharge between each shot while doing other things. So, on-board tank recharge time is not a big factor, but it is a consideration.}

#1 At 25 PSI inlet manifold pressure to the secondary compressor.

#2 At 60 psi manifold inlet pressure.

At 25 psi manifold pressure, the tank filled at a rate of 110 psi per minute. At 60 psi inlet manifold inlet pressure, it charged at well over 200 psi per minute. So, it took less than 1.5 minutes to hit 300 psi in the tank! The only downside of the 60 psi inlet charge is that the stage one pressure tank dropped pressure down to 80 psi in the process. So, I had to wait another 3 minutes after the cannon was filled, to allow the in-board tank to refill. That is not a big deal, however, because after one shot, I normally walk down range to check the damage and retrieve my slug (if possible). It seems about a 2 minute fill time is ideal because the on-board tank can refill in only a couple minutes after firing and I am ready to shoot again.

I am VERY happy with this compressor!

Matt
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Unread postAuthor: High-PSI » Thu Apr 05, 2012 4:48 pm

I just got done doing some additional testing.

I have an old scuba tank that is 8 inches in diameter and 22 inches long. It took 20 minutes to charge that tank to 550 psi. Not too bad, I suppose. It is good knowing I have a large volume tank I can charge at home to have some additional capacity at the field when I go shooting. I plan on setting up a decent regulator for it soon.

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Unread postAuthor: sharpshooter11000 » Thu Apr 05, 2012 4:59 pm

Would that be the maximum you could fill it to? It would be good to have a tank that you can take with you in a car and get lots of shots from.
Any pictures of the compressor(s) with the top cover?
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Unread postAuthor: High-PSI » Thu Apr 05, 2012 5:36 pm

I will get some pictures with the cover on soon. I need to cut two holes in it for lines to pass through before I mount it.

I can go far higher than 550. I stopped there because my stage two compressor was getting hotter than I wanted to see. So, I shut it down. I also need to get some decent high pressure couplings. I am using standard 200 psi compressor couplings. I have hit 800 psi with them on one cannon and the coupling was fine. But, I do not want to trust that with this much volume.

I bet I could get faster fill by fine tuning the precharge pressure. I will see.

I may add a fan to the second stage compressor as I have on the first stage. I did not think I would ever need it because the first stage tends to run much longer on average than the second stage. But, obviously, heat is an issue with very large volume at high pressure.

Oh, also, part of the heat was because I charged the scuba tank to 100 psi, then purged it to clear the tank. Then I did the same at 200 psi. After that, I let it run all the way to 550. So, the darn thing ran for around 40 minutes straight, and much of that time was at relatively high pressure. That is one thing I never considered when building this is the fact that higher pressure builds heat faster than lower pressure. I mean, it runs fine charging up the cannons. But, charging large tanks like this is a different story.

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Unread postAuthor: High-PSI » Sat Apr 07, 2012 12:49 pm

BLOWN COMPRESSOR. :shock:

I have been doing more and more testing with my compressor and I finally blew my second stage compressor. Either the head gasket or the reed valve is blown. Just like the other 1,000 psi compressor build on the board, my compressor runs but will not create any pressure. Stage one is fine.

I think I know why this happened.

I have been testing this thing up beyond 1,000 psi. However, that was in short bursts. I have also aired up my 2 gallon cannon to 350 psi without any problems. However, when I filled my big scuba tank, I blew the compressor. I filled it the other day to 550 psi and it was fine. However, I stopped because the compressor was getting hot. Today, I wanted to see how far it would go before the internal thermal cut out. Well, at 600 psi (only 14 minutes of fill time to reach 600 psi) the compressor stopped pumping. It was 130 degrees on the outside of the can when this happened. So, my guess is, fridge compressors are fine for high pressure, or filling large tanks, but not both at the same time. I am thinking that the heat, combined with high pressure blows them. Because, again, short fills at very high pressures seem to be fine. It is the long fills at high pressure that seems to be the issue.

Anyway, in the real world of shooting, this thing would only run for a few seconds over 500 psi and that for only one of my cannons. So, I could always replace the compressor with another fridge compressor and be fine. However, I went ahead and ordered a R22 dehumidifier compressor (new on eBay for $70 shipped) to try out. Technician recommended an R22 compressor to another poster in another thread. He said they run higher pressures.

That is my experience with this. I will let you guys know how it goes.

If nothing else (if the R22 compressor does not work well), I will replace it with the identical unit it had and know what NOT to do in the future and keep the long fills to a lower overall pressure.

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Unread postAuthor: wyz2285 » Sat Apr 07, 2012 1:30 pm

Thank you very much for doing this, now I know what not to do with my fridge compressor. Thanks!
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Unread postAuthor: Gun Freak » Sat Apr 07, 2012 2:03 pm

That sucks, but also adds info to our fridgy database :lol:

Good thing I only use mine at under 500 psi and for no more than 30 second intervals.
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Unread postAuthor: Goats spudz » Sat Apr 07, 2012 2:48 pm

my fridge compressor on its own (1 stage) reaches 1000 psi in under 30 seconds and its tiny
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Unread postAuthor: High-PSI » Sat Apr 07, 2012 2:56 pm

Try running it high pressure for a long time.

Heck, this thing hit 1050 psi in 3 seconds into a tiny tank.................
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Unread postAuthor: Goats spudz » Sat Apr 07, 2012 3:01 pm

i only use it for filling my pcp to 1000psi takes about 2 minutes i might get another but i have some milling to do! :D
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Unread postAuthor: High-PSI » Fri Apr 13, 2012 4:06 pm

Ok, I found a problem with running R22 dehumidifier compressors; the compressor inlet goes directly to the pump while the output pressurizes the compressor can. Typical frige compressors have the can on the low side not the high side. So, this cannot be used as a stage two compressor because the entire can will be pressurized.

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