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Small high pressure air compressor ideas

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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Small high pressure air compressor ideas

Unread postAuthor: BigBang J » Wed Mar 02, 2011 10:16 pm

Hi guys, I want an air compressor that can go up to 1000psi.
I have tried a mini fridge compressor but it died on me and wont compress air anymore. I haven't thought much about it yet, but I was wondering if any of you guys have tried to build anything like this.
Also does anyone know what would be the best piston seal design, would it be better to use o-rings or to use a cup seal on the face of the piston?

I was thinking about making something like a fridge compressor is built only better built, cause a fridge compressor can get those high pressures it just can't last long pumping those pressures.

Well what do you guys think, I haven't had time to work on this yet but I thought I'd sound you guys out first.

Thanks in advance for any advice.
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Unread postAuthor: Lockednloaded » Wed Mar 02, 2011 10:35 pm

There's something called a shoebox compressor used to top off HPA tanks, search it on youtube.

as far as a pump head seal is concerned, either method will work, cup seals are used on some HP multi-pump air guns, and floating o-rings have been used at 1000 psi by SF members
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 02, 2011 10:42 pm

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Unread postAuthor: Lockednloaded » Wed Mar 02, 2011 10:55 pm

I'd never seen that thread JSR, thanks for bringing it up. Do you think a drill motor could be used for a shock pump, and how would you keep the shock pump cylinder cool?
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 02, 2011 11:15 pm

Lockednloaded wrote:Do you think a drill motor could be used for a shock pump


Yes but it would probably need gearing down if you wanted to reach high pressures, note how the FX pump uses a pulley with quite a significant disparity in diameters.

how would you keep the shock pump cylinder cool?


Either deck it with fins and run a fan over it, or more likely coat it with a jacket with inlet/outlet pipes and pump coolant (oil/glycol/water etc.) through it, either from a larger reservoir or if compactness was an issue through a small radiator.
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Unread postAuthor: Lockednloaded » Wed Mar 02, 2011 11:32 pm

I would think a decent power drill could have enough torque for a small shock pump on a cam, but I've been wrong...a lot

As for cooling, maybe I could use a larger pipe around it filled with water and then fans all around?
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 02, 2011 11:42 pm

My cooling suggestions were a little overkill ;) really a fan would likely be enough without actually modding the pump cylinder. I would only look into serious cooling if you were looking to fill high volume cylinders.
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Unread postAuthor: Lockednloaded » Thu Mar 03, 2011 12:06 am

ehh If I had a pump to spare then maybe.... I think I'll try out the shock-pump-muli-stroke-hybrid-fueling-thing-a-mabob first
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Unread postAuthor: Crna Legija » Thu Mar 03, 2011 12:13 am

your compressor was probably faulty or a crap brand, my one has been going for 2 years now quite often hitting 950 psi and its from a fridge that was 20+ years old(it was made in Yugoslavia).
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Unread postAuthor: BigBang J » Thu Mar 03, 2011 10:05 pm

-_- wrote:your compressor was probably faulty or a crap brand, my one has been going for 2 years now quite often hitting 950 psi and its from a fridge that was 20+ years old(it was made in Yugoslavia).


Ahh, That is very encouraging. The compressor I had was from a pretty new Fridgidaire mini fridge, which most probably means it was a piece of junk. I will try to get an older and better made one.

JSR thank you for the link to the stirrup pump, I am checking that out.
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Unread postAuthor: jackssmirkingrevenge » Thu Mar 03, 2011 11:13 pm

BigBang J wrote:a pretty new Fridgidaire mini fridge, which most probably means it was a piece of junk.


I would look for a better quality fridge compressor first, or even better as suggested before, connect two to eachother to reduce the stress.
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Unread postAuthor: BigBang J » Fri Mar 04, 2011 9:18 pm

jackssmirkingrevenge wrote:
BigBang J wrote:a pretty new Fridgidaire mini fridge, which most probably means it was a piece of junk.


I would look for a better quality fridge compressor first, or even better as suggested before, connect two to eachother to reduce the stress.


How do you mean? in series or parallel
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Unread postAuthor: saefroch » Fri Mar 04, 2011 11:15 pm

In series. The stress that JSR is referring to is based only upon the pressure differential that each individual compressor generates, so instead of using one compressor to go from 0psig to 1,000psig, you use one to go from 0psig to 500psig and the other to go from 500psig to 1,000psig, each only sees a 500psig pressure differential, and it requires each compressor to only apply half as much force onto the pump head as it would if you use just one.

You could also fill a tank with twice the volume as your chamber to half the pressure desired, then connect that to the input of your compressor and halve the stress that way.
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Unread postAuthor: BigBang J » Sat Mar 05, 2011 10:01 pm

saefroch wrote:In series. The stress that JSR is referring to is based only upon the pressure differential that each individual compressor generates, so instead of using one compressor to go from 0psig to 1,000psig, you use one to go from 0psig to 500psig and the other to go from 500psig to 1,000psig, each only sees a 500psig pressure differential, and it requires each compressor to only apply half as much force onto the pump head as it would if you use just one.

You could also fill a tank with twice the volume as your chamber to half the pressure desired, then connect that to the input of your compressor and halve the stress that way.


But this method would require 2 of the same compressors, right?
because if you have 2 different compressors and one doesn't pump quite as much as the other you would either starve the second compressor in the series, or you would over pressurize the second compressor in the series. Is this correct?

I have some aluminum rod and tubing stock left over from a hybrid that I am working on. 1/2" rod and 1/2" ID x 1" OD tubing. I am thinking of using these materials to make a high pressure compressor. Do you think that the 1/2" piston will be small enough to generate the high pressures, or do I need a smaller piston dia.? I have an extra 3/4" hp induction motor laying around that I thought I could power it with.

And does anybody have a drawing of how the fridge compressor works?
Like the piston and valve body, check valve etc.?
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Unread postAuthor: jackssmirkingrevenge » Sat Mar 05, 2011 11:37 pm

[youtube]http://www.youtube.com/watch?v=bAZGkny8g64&feature=related[/youtube]

But this method would require 2 of the same compressors, right?
because if you have 2 different compressors and one doesn't pump quite as much as the other you would either starve the second compressor in the series, or you would over pressurize the second compressor in the series. Is this correct?


This could be an issue if there was a large disparity between the compressors but otherwise I wouldn't worry about it.

I would do it like this, though again only if there was a considerable difference in compressors:

larger compressor -> accumulator tank -> regulator -> smaller compressor
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