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Filling a HUGE cannon with piston.

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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Filling a HUGE cannon with piston.

Unread postAuthor: DinerKid » Tue Jul 14, 2009 5:23 pm

So i am planning out a cannon that is going to be huge like bigger than 10 gallon it should have a chamber made of 3 10 foot lengths of 3" pipe. the issue is with such a large chamber is that filling with an equalization hole could take forever. i was thinking about putting another quick connect into the chamber and regulating it slightly lower than the pilot area and filling both by putting some kind of a Y adapter to my air compressor but i want some other options and i was wondering if anybody had any.
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Unread postAuthor: spudtyrrant » Tue Jul 14, 2009 6:05 pm

thats about the exact same volume as mobiles cannon actually (roughly 2500ci).
its going to take about the same amount of time no matter what you do if you filling from a small diameter hose if you have like a 1/2 inch diameter hose running out of you compressor and a half inch ball valve then it might speed up filling noticably but i would just suggest filling the cannon with just the equalization hole it doesn't take long enough to be worth running two hoses and two regulators imo
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Unread postAuthor: Technician1002 » Tue Jul 14, 2009 6:13 pm

The easy solution is a pair of 1/4 turn ball valves and quick connects. Once the valve is blown closed with a shot into the pilot and a small (less than 1 PSI) holding pressure is built into the chamber, move the hose and blast the chamber full.

My Mouse Musket on a much smaller scale had the same filling problem as the fill is on the chamber and the piston did not use a spring. It's filling procedure was just a little different. The barrel was plugged and the chamber filled to a couple PSI. The plug was pulled. This sudden drop in the barrel sealed the piston. Then the chamber could be filled at any rate I wanted.
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Unread postAuthor: spudtyrrant » Tue Jul 14, 2009 6:19 pm

well i see a problem with that solution tech if he filled the chamber fast enough after he close the valve with the 1psi(most pistons that large take more) and built up lets say 2psi the valve would open
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Unread postAuthor: Technician1002 » Tue Jul 14, 2009 6:48 pm

spudtyrrant wrote:well i see a problem with that solution tech if he filled the chamber fast enough after he close the valve with the 1psi(most pistons that large take more) and built up lets say 2psi the valve would open


The EQ port was big enough to keep the pilot area above 25% of the chamber pressure during any fill I could shove through a tire valve. A close ratio (seat to OD) valve requires a very low pilot pressure to fire. In the case of the Mouse Musket, under 25% to fire.

A two inch piston at 1 PSI for example would have 3.14 lbs of force holding it closed. An area ratio of .75:1 would need the chamber pressure above 4 PSI while the pilot is at 1 PSI to fire. The small pilot area and eq port won't create the conditions required to fire on filling.

I filled it all the time this way. Plug the barrel, a quick shot of air, release the barrel and fill with full compressor flow. The Mouse Musket did not use o rings on the piston, but did use one on the valve seat. Moving friction is low.
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Attachments
PICT252.JPG
Mouse Musket valve in place.
MusketSeat.JPG
Mouse Musket valve seat.
PICT251.JPG
Piston and EQ port
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Unread postAuthor: mobile chernobyl » Tue Jul 14, 2009 8:48 pm

You won't have issues with the equalization holes unless your flowing some serious CFM ratings out of that compressor, and even then your flow will mostly be dictated by the poor flow of the quick-disconnect fittings. The main thing slowing down the filling of 10 gallon is the crappy on-board reg's that come stock on oh-so-many compressors. I have a really high flow one that reg's up to 150psi (my compressors limit anyways) but I need to rebuild it.

Good luck with your "big gun" and make sure you have a place to store it... and a way to move it! lol that's the main draw back for 10 gallon.

Some day down the line i will make my metal mini-avalauncher lol.
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Unread postAuthor: DinerKid » Wed Jul 15, 2009 9:05 am

well we have another 2 car garage we just finished to build an AC Cobra. right now the car is still being ordered and everything plus when we have it i will just use the lift or find a place to hang it.
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Unread postAuthor: psycix » Wed Jul 15, 2009 3:18 pm

Some compressors offer a plugged port on the tank, so you can fill faster bypassing the regulator.
If you need to make your EQ hole really big, simply install a check valve.
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