So just how can you get a relatively small amount of CO2 out of the main tank to propel an object as far as possible, and then be able to fire again immediately? It sounds kind of daunting, but I assure you it isn't hard at all. Just take the process step by step:







1. Get a "charge"



How can you get a uniform charge to shoot something? In our case, we have a large CO2 tank that produces pressures upwards of 800 psi. Yikes. We need to be able to break that down to about 20 to 100 psi. This is where a regulator comes into play. With a regulator, one can adjust the output pressure of gas from a source (the CO2 tank) to a manageable level. The one I got for this project has two pressure gauges - one to show the pressure in the tank and one to show the output pressure. I recommend this type since it gives the user a lot more precision with adjustments (plus it tells you when you're going to run out of gas). So now we have a steady supply of CO2. Now what?





2. Store that "charge"



With a consistent stream of propellant, we can trap some of that gas in another smaller chamber. We'll call this the secondary chamber. If we can direct the flow of the gas into such a chamber, we will have a set volume of CO2 at a set pressure - that of the regulator. It is this gas in the secondary chamber that is used to "shoot" the projectile. Therefore, we are not directly using gas from the large CO2 tank. It goes into a isolated (secondary) chamber so that we can shut off the flow of CO2 once the secondary chamber is filled. But still, we only have a smaller secondary chamber full of CO2. How does that propel an object?





3. The Main Valve



In order to be able to fill a secondary chamber and then release that pressure into a barrel on cue, we will need some special valves (Sorry, no ball valve cannons in this project). What we need is a valve that will direct a gas into a chamber/cylinder and then dump all of that gas into a different port when triggered. It just so happens that such a valve exists: a quick exhaust valve, or QEV. A QEV has three ports; an inlet port, a cylinder port, and an exhaust port. When a high pressure gas flows into the inlet port, a diaphragm inside the valve seals off the exhaust port. This allows all of the gas to flow through the cylinder port, or into the secondary chamber. Once the secondary chamber has reached its maximum pressure (as set by the CO2 regulator), the gas between the diaphragm and the inlet port can be vented to the atmosphere (when it's time to fire the cannon). Because of the pressure differences around the diaphragm, it will have a net force acting upon it and move in the direction of the venting gas. This exposes the exhaust port. Now, since the diaphragm is blocking the path to the atmosphere through the inlet port, the gas will rapidly "exhaust" through the exhaust port and the secondary chamber will empty. This happens in a fraction of a second.





4. The Fill Valve



So now with a QEV we can "fire" from what's in the secondary chamber. The only problem now is that we have to vent the inlet port of the QEV. We'll need another special valve for this. This valve needs to let gas pass through it into the QEV and then, after a trigger from an electrical current or push-button or something, it opens up a new pathway from the inlet port to the atmosphere. Luckily, such a thing also exists. This valve is called a directional control valve (DCV), or, in this specific instance, a 3-way 2-position directional control valve. This type of valve also has 3 ports. They are typically oriented with 1 port on one side and 2 on the other. The lone port on the first side will connect to the inlet of the QEV since it is this lone port on the DCV that will "connect" to either of the two other ports, depending on the position of the solenoid or valve internals (depending on your particular type). Think of a DCV as a momentary, normally closed single pole double throw electrical switch. Just replace the electricity with a flow of CO2. The normally closed position will allow for an automatic connection to the main CO2 tank for filling after each shot. Once the valve is energized or toggled, the secondary chamber will be effectively isolated from the main chamber. Toggling the DCV will also "trigger" the QEV, dumping all of the CO2 from the secondary chamber straight into the barrel. This is how you will fire the cannon. Pretty awesome, right?



For more information, click here.



Credits to http://www.valvehydraulic.com for the QEV diagram and http://www.pirate4x4.com for the DCV diagram.