Network Learning Project Update

One of the key components for this air cannon is the valve.  The purpose of the valve is to control when the air pressure in the reservoir tank is released into the barrel.  This is essentially the trigger mechanism that allows you to launch the projectile.  The two most common methods are a ball valve and a sprinkler valve.  Ball valves consist of a brass valve with a quarter turn lever that opens or closes the valve.  You are most likely to see them in your basement near the furnace, they are usually used for water not air pressure.  These are incredibly simple and robust designs since they are metal and can withstand as much as 300 psi as long as you get the right kind.  The downside to a ball valve is the lever.  Turning a lever in order to fire the cannon is effective but awkward which makes it difficult to aim.

The more elegant and popular alternative appears to the sprinkler valve design.  This method entails modifying an electronic sprinkler control valve in order to release the cannon's air pressure.  These valves make for better triggering mechanisms because they require less force to actuate.  When used as intended they are wired up to an electrical control circuit which actuates a smaller solenoid valve. There is a spring loaded rubber diaphragm inside the the valve body which separates it into two air chambers.  When first pressurized the diaphragm opens and leaks a small amount of air to the other side of the chamber.  This pressurizes both chambers equally which puts them in a balanced state.  While balanced the spring holds the diaphragm in the closed position.  In this balanced state the air pressure on each side counteracts one another and the spring is needed to hold the diaphragm in the closed position.  This is where the solenoid valve comes into play.  The solenoid acts as an electronic vent.  When it is actuated it opens and vents a small amount of air from one side of the chamber.  This vent  results in a sharp pressure differential.  When the pressure on one side of the diaphragm suddenly drops the valve becomes unbalanced and the higher pressure on one side of the diaphragm overcomes the spring tension which pushes it into the open position thus releases all of the air pressure in the reservoir very rapidly.  This more complicated design  uses a low force event to trigger a higher force result which makes it much more suited for a trigger type mechanism.

The downside to the sprinkler valve is that the electronic solenoid valve vents air too slowly which means that the air pressure isn't released into the barrel quickly enough to be efficient.  To liven up the valve's response time modifications need to be made which replace the solenoid with a higher flow mechanical compressor trigger.  The video below is an excellent tutorial for this modification and helped me to understand what is going on inside the valve.

Sprinkler Valve Modification