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At a loss here... Pressurizing my cannon

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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At a loss here... Pressurizing my cannon

Unread postAuthor: Alex345 » Sun Jan 17, 2016 7:04 am

Here's my problem; I'm building a +-25 bar cannon with a rather large chamber and small pilot volume, so using any type of manual pump would have a chance of the pilot losing it's pressure by the time i'm done filling the main chamber.

I had a fridge compressor, but all the oil ran out during it's removal from the fridge, and it recently just clicked and won't turn on anymore... I also have a 300 bar scuba tank, but i can't find ANY used (o²) regulators that go beyond 16 friggin bars! And buying a brand new one is just crazy expensive.

Any thoughts? I'm putting this project on ice to focus on another more low pressure project till i can find a decent pressure source.
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Re: At a loss here... Pressurizing my cannon

Unread postAuthor: jrrdw » Mon Jan 18, 2016 10:33 am

Both chambers should fill at same rate. Any leaks from the pilot?
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Re: At a loss here... Pressurizing my cannon

Unread postAuthor: Alex345 » Mon Jan 18, 2016 12:15 pm

Ah yes i'm sorry i forgot to add; The valve is not a homemade piston valve but an actual industrial piston valve. The surface area of the pilot piston is less then that of the piston that seals the chamber. So the pilot pressure needs to be higher then the camber by a few bars. So the pilot cannot be connected to the chamber unless you would put a small regulator in between them.

The pilot piston once had a hole in it (made from aluminum) which i tapped and screwed a teflon wrapped bolt in, so there might be a veeeeery tiny leak in it.
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Re: At a loss here... Pressurizing my cannon

Unread postAuthor: jrrdw » Mon Jan 18, 2016 1:28 pm

Fill from the pilot side. Is that a option that's doable in your setup?
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Re: At a loss here... Pressurizing my cannon

Unread postAuthor: Alex345 » Wed Jan 20, 2016 5:31 pm

Because of the pressure difference, the pilot and chamber are not connected to each other. I could connect them with a piece of copper line, but there would need to be a regulator in between them.

But the main problem is finding a pressure source... Would it be safe to hook it up to the 300 bar tank and open the valve REALLY slowly? Or would the pressure go up way to fast for that?
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Re: At a loss here... Pressurizing my cannon

Unread postAuthor: bravootome » Thu Jan 21, 2016 11:56 am

add a spring behind the piston. ( feel the barrel end if loose air during inflation )

The fridge comp. may be fixed by removing it's thermal resistance from the scheme .


users : let's take a competition going....like 40 m accuracy or 40m damage tests....now at this extreme weather condition ( -25 C)

If agree, scheduel(?) it next 3-4 days so we check the spud. the winner take it all.;)
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Re: At a loss here... Pressurizing my cannon

Unread postAuthor: Alex345 » Thu Jan 21, 2016 1:29 pm

hmm, the space where the spring would need to be placed is already very tiny tho. But, i looked at the compressor again after what you said about the thermal device and i found a small round piece of plastic that was in no way connected to the compressor. It just hugged the outside of the housing...

I bent it away from the housing and she seems to keep running now, i placed my finger where it contacted the housing but felt no heat at all? I'll get the right fittings asap and solder a long piece of ductile copper line to the comp and i'll at least have a way to (hopefully) pressurize it before the lack of oil catches up to me.

And sure thing i'm up for that if i can get her working in that short time frame! It's just not nearly as cold here tho :)
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Re: At a loss here... Pressurizing my cannon

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Re: At a loss here... Pressurizing my cannon

Unread postAuthor: bravootome » Thu Jan 21, 2016 2:32 pm

"that thermic resistance " does not worm up , it shuts of the motor if something is wrong. So for what we use it, there is no need for protection. this is a way to resuscitate old used compressors .
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Re: At a loss here... Pressurizing my cannon

Unread postAuthor: Alex345 » Sat Jan 23, 2016 7:53 am

Oh ok i thought it was some kind of anti-overheating sensor, that's why i touched the housing to see if it was warm :) Since a lack of oil can cause overheating.
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Re: At a loss here... Pressurizing my cannon

Unread postAuthor: Alex345 » Sat Jan 23, 2016 4:03 pm

And it works! Just shot a rolled up washcloth at almost 20 bars! Made the cannon jump up quite a bit too :D

It fills the very small pilot in a snap, but the chamber just takes for ever tho... It would awesome to find 2 exact same compressors and hook them up together for twice the filling speed. Maybe freezer or even aircon compressors would be more powerful then the ones from a fridge?
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Re: At a loss here... Pressurizing my cannon

Unread postAuthor: ramses » Sun Jan 24, 2016 12:13 am

Alex345 wrote:And it works! Just shot a rolled up washcloth at almost 20 bars! Made the cannon jump up quite a bit too :D

It fills the very small pilot in a snap, but the chamber just takes for ever tho... It would awesome to find 2 exact same compressors and hook them up together for twice the filling speed. Maybe freezer or even aircon compressors would be more powerful then the ones from a fridge?


People have fed the input of fridge compressors with shop air to increase the mass flow rate (conserving the volume flow rate), by a factor of roughly the gauge pressure at the input in atmospheres.
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Re: At a loss here... Pressurizing my cannon

Unread postAuthor: bravootome » Tue Jan 26, 2016 11:53 am

Alex345 wrote:And it works! Just shot a rolled up washcloth at almost 20 bars! Made the cannon jump up quite a bit too :D

It fills the very small pilot in a snap, but the chamber just takes for ever tho... It would awesome to find 2 exact same compressors and hook them up together for twice the filling speed. Maybe freezer or even aircon compressors would be more powerful then the ones from a fridge?


for very high output and same pressure as fridge comp, can be used a compressor from an air cond. unit. i do find them at scrap metal yard.......or so...or recycling .....in your contry....
but i do not use it cause it shackes much and it warms up my chamber's gun...
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