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Experience in cascaded air compressors?

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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Experience in cascaded air compressors?

Unread postAuthor: boyntonstu » Wed Feb 03, 2010 5:09 am

Have you experience in feeding a refrigerator or a/c compressor with another?

What was the input/output pressures?
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Unread postAuthor: psycix » Wed Feb 03, 2010 3:48 pm

You can't cascade em like that, as the shell is not made to hold a lot of pressure.
You may, however, improve the flow output by feeding it with a few bar of pressure. More air intake = more air out.
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Unread postAuthor: boyntonstu » Wed Feb 03, 2010 4:27 pm

psycix wrote:You can't cascade em like that, as the shell is not made to hold a lot of pressure.
You may, however, improve the flow output by feeding it with a few bar of pressure. More air intake = more air out.


AFAIK The case shell pressure should not exceed 200 psi.

If we feed an a/c compressor with 100-200 psi what would we expect as the final pressure?
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Unread postAuthor: POLAND_SPUD » Wed Feb 03, 2010 4:50 pm

apparently it would be lower than normally... I don't remember who tested it...

jimmy suggested that one could increase pressure by reducing pressure on the input side
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Unread postAuthor: Jeeperforlife » Wed Feb 03, 2010 4:57 pm

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Unread postAuthor: POLAND_SPUD » Wed Feb 03, 2010 5:13 pm

I knew about that one but someone else has tested it a couple of months ago and the results were completely different (larger flow but at lower pressure)


@boytonstu
hey would you be so kind as to test it ? so that we could sort it out once and for all?

measuring pressure won't be a problem but I think that you could use water displacement to measure flow
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Last edited by POLAND_SPUD on Fri Feb 19, 2010 5:34 pm, edited 1 time in total.
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Unread postAuthor: psycix » Thu Feb 04, 2010 4:40 am

I'm going to run one out of its shell and feed it directly by machining a custom piston housing cap.
Give me a few weeks and you'll see a topic appear.
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Unread postAuthor: scianiac » Thu Feb 04, 2010 6:24 pm

I would think that the only thing that determines flow and pressure is the containment. If the output is fed into a pressure vessel as the pressure increases the flow decreases as a higher pressure gas is left in the piston on each stroke meaning less gas is put in the piston on the intake. But I've never heard of anyone getting more than 400 psi. My pump is out of a car refrigerant recycler and it will push the pressure right to about 400 psi. At that pressure the motor stalls which I would think would happen to you pretty quickly if you start building a multi-stage compressor. If you do want to try I would suggest the biggest maybe oldest pump you can find for the secondary.
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Unread postAuthor: Brian the brain » Thu Feb 04, 2010 6:56 pm

But I've never heard of anyone getting more than 400 psi.

I shut mine down at 900.After my share of accidents I have become a lot more cautious..

No telling what it would have done..it would probably have done another 100 psi before grinding to a halt.

I don't know where you got your info, maybe first hand, but with a bad compressor.
Input pressure does make a difference as the bottom of the piston is exposed to the incoming pressure.
This means the piston is aided by the pressure on the up stroke, so it can reach higher pressures with the same effort.

In theory that is.
I haven't tried it.

Poland_Spud is right..it needs to be settled for sure..
Not by me though.
I felt 900 psi was plenty.Although I have combined two to get higher flow, wich was great IMO.
Too bad one died.
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Unread postAuthor: boyntonstu » Thu Feb 04, 2010 7:40 pm

Brian the brain wrote:
But I've never heard of anyone getting more than 400 psi.

I shut mine down at 900.After my share of accidents I have become a lot more cautious..

No telling what it would have done..it would probably have done another 100 psi before grinding to a halt.

I don't know where you got your info, maybe first hand, but with a bad compressor.
Input pressure does make a difference as the bottom of the piston is exposed to the incoming pressure.
This means the piston is aided by the pressure on the up stroke, so it can reach higher pressures with the same effort.

In theory that is.
I haven't tried it.

Poland_Spud is right..it needs to be settled for sure..
Not by me though.
I felt 900 psi was plenty.Although I have combined two to get higher flow, wich was great IMO.
Too bad one died.


This means the piston is aided by the pressure on the up stroke, so it can reach higher pressures with the same effort.

What happens during the down stroke?
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Unread postAuthor: psycix » Fri Feb 05, 2010 2:35 pm

jimmy suggested that one could increase pressure by reducing pressure on the input side

Compressing the air requires a certain amount energy. Feeding it with more air while putting the same amount of energy per second in, will at least lower your RPM, and possibly, when fed with too much, stall the compressor.
In reverse, less air to compress gives you more energy available per volume of air. More energy/air, more pressure.
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Unread postAuthor: Brian the brain » Fri Feb 05, 2010 2:42 pm

???
It goes against my gut feeling...

Please...can someone other than maggotman try this??
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Unread postAuthor: ramses » Fri Feb 05, 2010 4:00 pm

In a piston type compressor, depending on the internal arrangement, it could increase pressure by whatever the input is (100psi, or whatever), as well as increasing flow by a factor of the absolute input pressure in bar. For this to occur, Both sides of the piston would have to be exposed to the input pressure, creating a net force of 0. The input pressure would also increase the amount of air in the pump, artificially increasing the compression ratio. The extra energy comes from the motor applying more force from the motor compressing what ends up being an air spring with a large reservoir on the up stroke. I have plans for a 3 stage pump, once I find a way to gear down a gasoline engine to produce the required torque.
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Unread postAuthor: boyntonstu » Fri Feb 05, 2010 5:34 pm

FROM:

http://www.airgununiverse.net/community ... 207.0.html

"
I finally was able to get the compression fitting I needed for linking my regular shop compressor to my refrigerator compressor. My first test is not to see what kind of pressure I can achieve, but rather how much faster I fill a 20 oz CO2 cylinder to 400 psi. The refrigerator compressor by itself takes 4 min 24 sec. Using my shop compressor feeding its input 100 psi, the time is only 1 min 30 sec. That is a significant time savings, almost 3 minutes saved."


FWIW Some new data.
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Unread postAuthor: POLAND_SPUD » Fri Feb 05, 2010 5:57 pm

hmmm interesting... could you convince him to test max pressure as well ?
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