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Semi Auto and Regulators Help

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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Semi Auto and Regulators Help

Unread postAuthor: Major Collins » Mon Nov 23, 2009 6:43 am

ok for a double chamber / ball valve semi auto idea , if i have a primary chamber that can be filled to 400 psi how big does the secondary chamber has to be so i can get decent fire power? (when i bleed the air in to the secondary chamber - how much psi is effect enough for shooting a marble with power ?)

Where or how do i make a regulator to regulate air into the secondary chamber?

where do i place the regulator?
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 23, 2009 6:55 am

Your system needs to be as follows:

[large primary chamber]--[regulator]--[small secondary chamber]--[valve]--[barrel]

Assuming the reg is set to 100 psi, and you're using an efficient valve (QEV/piston) and a long enough barrel (at least 2 feet or so), it should be enough to put a marble clean through 3/4" plywood. The secondary chamber should have roughly the same volume as your barrel. The size of your primary chamber depends on how many shots you expect to get from the system per fill.

Your best bet is to buy a regulator, have a look around ebay, there are some good value ones available, though if you intend to start with 400 psi you have to check if it will take that kind of input. Also, how do you plan to get to 400 psi in the first place?
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Unread postAuthor: Major Collins » Mon Nov 23, 2009 7:29 am

jackssmirkingrevenge wrote:Your system needs to be as follows:

[large primary chamber]--[regulator]--[small secondary chamber]--[valve]--[barrel]

Assuming the reg is set to 100 psi, and you're using an efficient valve (QEV/piston) and a long enough barrel (at least 2 feet or so), it should be enough to put a marble clean through 3/4" plywood. The secondary chamber should have roughly the same volume as your barrel. The size of your primary chamber depends on how many shots you expect to get from the system per fill.
ok i understand all this

i plan on using a qev and i have incorporated it into my design
ok my barrel is a meter long i would say that is good enough yes? and when you say put a marble through ply how much psi i do you think that shot would be?

well i got a gas bottle (looks a much like a fire extinguisher bottle)
and my uncle he is very smart and handy man as well i love him lol he made my bottle and say it should be fine at 400 psi. i pressurized it to 160 already as much as my bike pump will go
a check valve?
and i plan on using a shock pump to pump to 400 psi
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Unread postAuthor: Major Collins » Mon Nov 23, 2009 7:36 am

i could possibly use this method to check "the same amount of volume as my barrel" ..
block off or tape off one end of the barrel and fill with water to the top then pour water into a measuring cup and convert how much water there is into volume?
that would work right?
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 23, 2009 10:36 am

It's much easier to calculate the volume.

(half inner diameter) x (half inner diameter) x (pi) x (length of barrel)

If you use centimetres for all the dimensions, the result will be in cubic centimetres or mililitres.

i plan on using a shock pump to pump to 400 psi


Forget it, you will die of old age before you reach 400 psi. Shock pumps are only good for 10-20mL volumes, if you want more than that you'll have to use a fridge compressor or regulated high pressure bottle.

If you're stuck with 160 psi then you can simply make your primary chamber larger.

To give you an idea of power, have a look at this. With a good valve and a metre long barrel, 100 psi will be enough for your purposes.

In future you might decide that maybe that's overkill and you would be happy with the power at say 70 psi, then you could turn down the regulator and get more shots per fill with the same setup.
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Unread postAuthor: Major Collins » Mon Nov 23, 2009 10:17 pm

O.o oh really now? .... that sounds harder than what i wanted to do lol
well diameter i dont know and since i dont know how to find it out i will be stuck for a while .. well i could maybe get 300,350ish psi? out of a shocky,
i could maybe go 200 psi but my bike pump gauge doesnt say so i just stop at 160.

and im more of a power person lol i rather get fewer stronger shots then more weaker shots...

ohh i was reading over your first post and this diagram [large primary chamber]--[regulator]--[small secondary chamber]--[valve]--[barrel]
shouldn't there be a ball valve in between large primary and regulator?
also just on the regulator if i have the secondary chamber half the size of my barrel the regulator wont be able to force the psi in there right? so the regulator cant cram psi into a smaller space?
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