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Old 03-10-2008, 06:26 PM #1
QuencyJones16
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Minimum PSI needed to accelerate a paintball

Hello everyone,

I am trying to figure out the minimum PSI needed to fire a paintball. I have figure out that the average weight of a paintball is around 3 grams.

So Force would be;

mass (m)= 3gram = 0.003kilogram
acceleration (a) = 300 foot/second^2 = 91.44 meter/second^2

force (F) = 0.27432 newton

Now I need to know a way to convert this to psi, but I do not think there is one. If anyone could try and figure out a way to get this for me I would greatly appreciate it.

I need to know because I have a design of a bolt system ( Spool Valve) and need to know if the PSI that is needed to move the bolt (not much at all) will also accelerate a paintball as well, without an LPR.
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Old 03-10-2008, 06:29 PM #2
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i would but i have no idea either.
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Old 03-10-2008, 06:59 PM #3
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It probably won't work the way you want it to. You can move a bolt with less then a 100 psi, but it's hard to shoot at paintball with that amount of pressure. It's been done before, but it requires a large volume of air, effciency sucks, and recharge rates slow the gun down. You could up the bolt operating pressure, but then you would just be where guns were several years ago when guns didn't come with stock lpr's.
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Old 03-10-2008, 06:59 PM #4
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It all depends on the volume. A higher pressure means less volume of air, and vica cersa. I believe the minimum is 80psi. If it gets any lower then the ball is already out the end of the barrel before it can accelerate to the needed fps. But I could be totally wrong, b/c I'm talking out my ***.

Edit: to Snuggles, the bolt pressure can be different than the pressure shooting the paintball. Ex: a Quest's bolt pressure can be well below 100psi but the pressure shooting the ball is still above 200.
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Old 03-10-2008, 07:01 PM #5
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Quote:
Originally Posted by snuggles_smith View Post
It probably won't work the way you want it to. You can move a bolt with less then a 100 psi, but it's hard to shoot at paintball with that amount of pressure. It's been done before, but it requires a large volume of air, effciency sucks, and recharge rates slow the gun down. You could up the bolt operating pressure, but then you would just be where guns were several years ago when guns didn't come with stock lpr's.
true.

in my physics class they taught the amount of potential energy in 'X' amount of air in a given set of conditions. but if you expect me to remember anything from high school, youll have to invent a retroactive anti-hangover drug.
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Old 03-10-2008, 07:09 PM #6
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With this design there is only one moving part which is the bolt, which weighs around 7 grams, so it is not a lot. So I know it would not take a large amount of air to run the bolt. I could set it up to use an LPR and with its light weight would not take a lot of air to move the bolt.

I just need to figure this out so I can move on with my plans.
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Old 03-10-2008, 07:19 PM #7
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I would go with the lpr setup. With a bolt that light you could move it with an extremely low pressure, much lower then what's needed to shoot a paintball.

Benb1- I'm aware the operating pressure and shooting pressure can be differnt, but it requires an lpr. He's wanting to run his design without an lpr, which means the pressures would have to be the same.
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Old 03-10-2008, 07:23 PM #8
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Yeah it would not be hard to set up an LPR for it, I was trying to go for simple right now. I have a few LPR's lying around here that I can work with.

I am trying to see what materials would work the best for me. I need sturdy materials that will not break but are also slick, right now glass filled Delrin is my best bet, unless someone else has a better suggestion.
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Old 03-10-2008, 07:29 PM #9
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you need to take the PSI x the volume of air to find the amount of force. So it will be different for different guns.
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Old 03-10-2008, 07:35 PM #10
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Yes I know this, but I was just looking for an average of what it may be. The Dump Chamber will be around 2 1/4 cubic inches of space, but I still do not know what the PSI of the marker will be.
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Old 03-10-2008, 07:50 PM #11
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It all depends.

there are too many variables..

Are you using a bolt? Is the bolt moving electrically or does it rely on this air pressure we're measuring?
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Old 03-10-2008, 07:52 PM #12
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Solenoid actuated, relying on a vacuumed style to pull the bolt back into firing position.
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Old 03-10-2008, 08:42 PM #13
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this looks like a trial and error problem
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Old 03-10-2008, 08:43 PM #14
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Quote:
Originally Posted by QuencyJones16 View Post
Solenoid actuated, relying on a vacuumed style to pull the bolt back into firing position.
vacuum?! how the hell is that gonna work?
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Old 03-10-2008, 09:39 PM #15
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Quote:
Originally Posted by QuencyJones16 View Post
Hello everyone,

I am trying to figure out the minimum PSI needed to fire a paintball. I have figure out that the average weight of a paintball is around 3 grams.

So Force would be;

mass (m)= 3gram = 0.003kilogram
acceleration (a) = 300 foot/second^2 = 91.44 meter/second^2

force (F) = 0.27432 newton

Now I need to know a way to convert this to psi
, but I do not think there is one. If anyone could try and figure out a way to get this for me I would greatly appreciate it.

I need to know because I have a design of a bolt system ( Spool Valve) and need to know if the PSI that is needed to move the bolt (not much at all) will also accelerate a paintball as well, without an LPR.
Newton's are a unit of force, where as PSI is a unit of pressure. So, the conversion is not possible. While there is a way to find out the PSI that you need, I haven't had enough physics to tell you all of that. MVP might be able to answer that for you, though. He's the science major.

edit: also, you have to consider all of the different factors that change from instance to instance (i.e. actual paintballs used (brands, batches etc.), the different barrels (brands, lengths, etc.), and the list goes on)
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Last edited by AggiePBaller : 03-10-2008 at 09:42 PM.
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Old 03-10-2008, 10:10 PM #16
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And 300 fps is the muzzle VELOCITY, not the acceleration. To find acceleration, get a high speed camera and a chrono and time how long it takes for the ball to exit the barrel after you pull the trigger, then v/t=a


Then again, you are talking about force measured in Newtons, which can't really translate into psi, because it's all dependent on volume, velocity of the air etc.
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Old 03-11-2008, 12:24 AM #17
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I think you're going to want an Lpr to control the bolt. There is one variable you may not have thought of, and that is bolt-flyback from the valve firing. I learned about this after installing an MQ2 Valve in my Ebladed cocker.

The MQ valve, just to give you a background, eliminates the hammer, hammer spring, and poppit valve in an autococker, and replaces it with a solenoid-driven valve. So with the MQ valve, the cocking pressure (bolt-movement) is no longer tied in with valve's function. So in theory, you can run your Lpr way lower, because it no longer has to be powerful enough to compress the hammer spring and pull the hammer back - it only has to move the bolt back and forth.

So, to make a long story short - I set my Lpr very low (somewhere in the vicinity of 20-40 psi). On training mode (the valve doesn't fire - but the bolt cycles) the gun cycled just fine. I even got it to cycle up to 13bps with a rediculously low Lpr setting.

However, here's the catch - when I put it on normal semi mode and shot paint - the force of firing the ball caused the bolt to kick back some - resulting in blowback up the feedneck, and a slowed rate of fire. In my case, the blowback was so bad I could only shoot about 2 balls per second with the eye on. Once I turned the Lpr up to an adequate range (60 -70psi) - the bolt-flyback (and blowback) went away, and the gun fired away at blazing speeds.

So the bottom line is that even though a bolt can cycle back and forth easily with 20-30 psi - you'll run into problems with it when it needs to hold the bolt closed for a shot. This effect is more pronounced the lighter your bolt is, as well. In addition, this problem would not be limited to autocockers, it would happen on just about any gun with a lightweight bolt that's driven by pneumatics. I would say 60psi would be close to the minimum pressure needed.

Now, as far as 60psi being enough to propel a ball to 300fps - probably not. It may be possible, but you'd probably need a really long back section for a barrel, a really long dwell time, and you'd be using a huge volume of air to accelerate the ball - resulting in terrible efficiency. That's why I'd recommend seperating the two actions. Good luck, I'm interested in seeing your design.
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Old 03-11-2008, 12:36 AM #18
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Its not that simple. You need drag coefficients. You can accelerate a paintball with 1psi if everything was 100% efficient.
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Old 03-11-2008, 03:54 AM #19
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So i almost have a degree in engineering...

First off, like someone said, 300fps is a velocity, not an acceleration.

a = v/T
where the T you looking for is the time it takes the gun to travel 1/2 of a cycle (bolt from zero to forward), which is based on how many shots/second you want
*edit* that is assuming you want the ball to be at 300fps by the end of the bolt cycle, w/o accelerating down the barrel, which may be impossible

Also, The force in your F=ma equation, is the net force applied to the paintball, not including frictional forces on the ball, and the forces of air that escapes around the ball. also the force of your ram will have to be greater than this, because you will also have to accelerate the bolt up to a sufficient speed that it can cycle at that rate, but the bolt doesn't need to be going 300fps(unless your really not planning on using air to power the ball?).

finally a Newton is a unit of force, so is a pound. convert newtons to pounds(google) and then to find the psi, or pounds per square inch, divide the pounds by the # of square inches = (Pi)(r)^2 = (Pi)(.68in)^2

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Old 03-11-2008, 09:38 AM #20
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Ever hear of Dave Halls gas gun design tool? It was made for designing pneumatic spud cannons but it works well for paintguns too. http://thehalls-in-bfe.com/GGDT/
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Old 03-11-2008, 10:23 AM #21
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http://automags.org/forums/showthread.php?t=34429

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