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blow gun vs ball valve

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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Unread postAuthor: saefroch » Sun Nov 28, 2010 12:17 pm

I'm talking about a pilot for a piston valve. The opening speed of which and thus impact force is decidedly less than a spring-actuated ball valve.
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Unread postAuthor: Labtecpower » Sun Nov 28, 2010 12:57 pm

But the force YOU apply to it with pushing or pulling the handle is more than te impact force of a spring actuated ball valve.
I've made both a simple ball valve pneumatic, and one with a spring actuated ball valve, so I have experience with both situations.
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Unread postAuthor: saefroch » Sun Nov 28, 2010 1:09 pm

Labtecpower wrote:But the force YOU apply to it with pushing or pulling the handle is more than te impact force of a spring actuated ball valve.
I'm confused by this. Isn't the whole point of a spring-actuated ball valve that it opens faster? Fimpact = (m*(vi-vf))/t Assuming the mass of the moving parts are the same, the stop is the same and works in both occasions, F is directly related to vf. Since a spring opens a ball valve faster, vf would be greater.
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Unread postAuthor: Technician1002 » Sun Nov 28, 2010 1:14 pm

The ratio diameter of the piston valve seat to the diameter of the piston makes a huge difference in how a piston performs when piloted.

The closer the valve seat is to the OD of the piston, the lower the pilot pressure has to go before the piston will unseat.

The lower the pressure when it unseats, the harder it is driven open and the longer it remains open before the chamber is low enough so the remaining pressure in the pilot and pressure from compression (from the piston moving into the pilot) will keep it open longer before closing.

A narrow ratio piston with a larger pilot volume (too small of a pilot is bad as the air compresses raising the pilot pressure during the shot) will work very well without requiring a large high flow ball valve to keep up.

A spring actuated ball valve is a fix for pistons with too large a ratio, too small a pilot volume, or too big an EQ hole/piston leakage.

A proper piston valve goes hisss, BOOM. A super high volume hiss is not required to get the boom.

My Mouse Musket used to toss gumballs through 1/2 inch plywood. The original hollow piston and hollow pipe plug provided the large pilot volume. The o ring on the valve seat made the piston a narrow ratio. The lapped fit made the piston low leakage. Good performance was not an accident.
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Unread postAuthor: Labtecpower » Sun Nov 28, 2010 1:36 pm

We may have confused you, Tech, as the discussion was about building a cannon with the ball valve as the MAIN valve. you are talking about ball valve pilots. All you say is true, but not enirely related to the topic :wink:

@saefroch;

The impact force of the spring opened ball valve may be greater, but the force directly applied to the valve is greater when opened by hand.
the force applied by a spring is connected to the gun itself, so there isn't any force that pushes the gun out of aim.
however, when opened by hand, the force is applied from an external source, thus pushing away the gun.

:roll:

trying to make myself clear is pretty difficult in a non-native language...
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Unread postAuthor: Technician1002 » Sun Nov 28, 2010 1:47 pm

I was miss-led by this post;
I'm talking about a pilot for a piston valve. The opening speed of which and thus impact force is decidedly less than a spring-actuated ball valve.
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Unread postAuthor: jimmy101 » Sun Nov 28, 2010 2:33 pm

Labtecpower wrote:the force applied by a spring is connected to the gun itself, so there isn't any force that pushes the gun out of aim.

Nope.

The ball is rotating under the force applied by the spring connected to the gun. Therefore the gun itself is rotating in the opposite direction of the valve's ball. You can not remove that affect. A well designed setup might reduce it somewhat by using no more force than necessary, but it can't be eliminated.
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Unread postAuthor: FighterAce » Sun Nov 28, 2010 2:45 pm

Arent those forces minute if the ball valve opens easily and only needs a light spring? I'm sure it can be eliminated by proper hand placement / firing position or even increasing gun length and mass.
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Unread postAuthor: saefroch » Sun Nov 28, 2010 2:48 pm

Labtecpower wrote:the force applied by a spring is connected to the gun itself, so there isn't any force that pushes the gun out of aim.
however, when opened by hand, the force is applied from an external source, thus pushing away the gun.
Keep in mind you are also connected to the gun itself, you're holding onto it (though this is irrelevant). To test the second half, you could to an experiment like this (which I do not recommended): Grab a fairly heavy object, and hit yourself with it. The body part you hit will be pushed away from the impact, even though the large heavy object is connected to you, and from an "internal source." Momentum is conserved.

Physics is confusing.

FighterAce wrote:Arent those forces minute if the ball valve opens easily and only needs a light spring? I'm sure it can be eliminated by proper hand placement / firing position or even increasing gun length and mass.
Momentum, the product of mass and velocity, is conserved. So the greater the mass, the lower the velocity (this is also a way to calculate recoil, as the gun's momentum equals the momentum of everything coming out the muzzle). It cannot however be eliminated, but it can be made so minute as to be close to nothing.
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Unread postAuthor: wyz2285 » Sun Nov 28, 2010 3:29 pm

FighterAce wrote:
wyz2285 wrote: but in my opinion firing a spring open ball valve causes vibration that influence accurancy, if you are looking for high precision :wink:


I have shot 2000+ rounds through my M4 and never experienced what you describe. To get any amount of vibration, your ball valve handle should weigh more then 1 kg and have a spring powerful enough to move such mass. THEN you would get vibrations to influence your aim.

If you're a lousy shot after years of shooting theres not much that can help is there :D

A good test would be to aim at a target ~50 meters away while standing, dry fire and see if your reticle has moved / shaken off target. If you slap the trigger, the result of this test will obviously be invalid. If you dont understand the previous sentence, dont even attempt it.
Depend what do you mean accurant :wink: my best airgun it's able of hitting a can at about 70 ms at 200 psi, effective range is about 100 m :D
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Unread postAuthor: Technician1002 » Sun Nov 28, 2010 8:07 pm

jimmy101 wrote:The ball is rotating under the force applied by the spring connected to the gun. Therefore the gun itself is rotating in the opposite direction of the valve's ball. You can not remove that affect. A well designed setup might reduce it somewhat by using no more force than necessary, but it can't be eliminated.


It can be counter balanced however. An equal mass rotated in the opposite direction can counter balance the rotational force.

An engine with a counter rotating shaft does this. A second dummy ball valve can counter the rotational force of a single ball valve.

Here is a patent on it.
http://www.faqs.org/patents/app/20090107426
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 29, 2010 6:20 am

... and yet we still do not know what accuracy the OP was hoping to achieve :roll:

Some pointers in this thread on what factors you need to look at to ensure accuracy.
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Unread postAuthor: LovableAirGuns » Mon Nov 29, 2010 6:21 am

pictures of my gun ill try and get some of my piston and stuff.
If your wondering y there is a blow gun there it is because it did shoot with the blow gun but ever since i have changed the sealing face on my piston it just doesn't want to work, all the air just escapes out of the blow gun :(
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 29, 2010 6:35 am

You either have too much friction with your piston, or too much air can escape past the piston from the chamber into the pilot area.
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Unread postAuthor: LovableAirGuns » Mon Nov 29, 2010 8:05 am

ill add some pics of my piston tomorrow and other pics. thanks for all the help guys :D
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