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regulation 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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regulation help

Unread postAuthor: McThrust » Wed Feb 21, 2007 8:39 pm

ok guys i wanna make a marble gun that shoots more than once without having to pressurize again. The design i first thought of was to have the larger reservoir chamber -> regulator -> regulated firing chamber -> sprinkler valve ->barrel.

Though what i don't understand is what is the point of having a larger reservoir than the regulated chamber? say you have a reservoir 3 times the volume and 3 times the psi of the regulated smaller chamber; due to the fact that when the regulator is open (no pressure in the small regulated chamber) what the pressure will do is equalize between the two chambers until the regulator closes.

So for example if the small chamber is regulated to 30 psi and the reservoir is at 90psi you would only get 3 shots (including the first shot which is from the small chamber being filled when the reservoir is filled), with the fourth shot having the regulator open as there isn't enough pressure from the reservoir going into the small regulated chamber to close it, therefore it would be a crappy 4th shot. All because the pressure will try to equalize between chambers.

Now if this is true you would get exactly the same results as above with a reservoir that is the same volume as the small regulated chamber. so whats the point of having a larger volume reservoir if the amount of shots you get is directly related to psi and not reservoir size????

either theres something i'm missing or i'm just completely wrong. Probably both.

any help would be appreciated.
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Unread postAuthor: noname » Wed Feb 21, 2007 8:44 pm

The pressure will not equilize, unless your regulator is set to the pressure of the larger tank. These figures relate to a launcher I have, my main tank is 5 gallons at 115 psi (air compressor) and the cannons chamber is like 3/8 gallos or something, and I set the regulator to 90 psi. This means when I fill the cannon, it fills to 90 psi, and leaves the compressor with about 109 psi, then 102 after shooting, then 95 after shooting again, then 88, and the pressure of the tank and cannon are equal.
Hope that was a somewhat good explanation.
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Unread postAuthor: McThrust » Wed Feb 21, 2007 8:55 pm

i realise now that a large and a small reservoir at the same psi cant give the same amount of shots. but why?
How is it that so little of the large reservoirs pressure is taken after each shot??? damn i wish i knew more about the physics governing pressure!

but thanks alot for your help.
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Unread postAuthor: noname » Wed Feb 21, 2007 9:18 pm

"i realise now that a large and a small reservoir at the same psi cant give the same amount of shots. but why?"
That part seems pretty obvious, or maybe just to me. The larger reservoir has more air, because it's bigger.
As for your second question, it's just the size of the tanks are so much different. If you worked it out by calculating volume and pressure of each tank, minus how much pressure from the larger tank each time, you could probably work out an equation that would work for any gun. It would just take about 20 minutes to create such an equation.
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Unread postAuthor: McThrust » Wed Feb 21, 2007 9:28 pm

ahh i think i understand

i forgot to take into account that 1psi in a large tank is worth more in a smaller tank, and when the regulator is open therefore making one big tank (both tanks combined for a split second before the small tank is filled again) the small regulated tank only takes very little of the large tanks pressure before it closes.

thnx mate
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