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The solenoid used in the Ion was a valve designed specifically for the marker by Smart Parts themselves, in cooperation with Tri-Tech development. It is designed to mount directly to the marker's electronics and include one input and one output through the top. The Ion solenoid is a type of encapsulated three-way. It is different from other common solenoids in that there isn't a balanced spool or valve section that moves back and forth. Instead, the internals consist of a cylindrical armature with moves up to fire and back down to go idle. The Ion solenoid is encapsulated, meaning it's all one piece surrounded by the core. While the solenoid is idle, air pressure enters through the top and pushes down on the armature, which seals the exhaust vent at the bottom of the housing. The chamber where the armature resides is octagonal in shape, to allow air to be directed to the bottom of the armature, as well as providing a gliding surface to guide the movement of the armature up and down. The space between the armature and the inside walls of its chamebr is small enough that the armature will maintain a seal on the bottom, but once its moved up air pressure will be able to vent around it. At the top of the armature, air is also allowed to shunt up through the output and reach the front of the bolt (to keep it open). When the valve becomes energized, the armature is lifted upward, which allows the pressure pushing the bolt open (the output) to vent back into the solenoid and out through the bottom. At the same time, the armature seals off the inlet to the valve at the top, to prevent air from leaking out during the energized time. The seal isn't perfect, but it does te job for the small dwell time the marker uses. Once the dwell time has expired, the armature is pushed down to once again seal the valve and allow pressure to output while the marker rests idle. Performance: The first noticeable thing about the Ion solenoid is the very large coil that surrounds the housing. The above diagrams aren't exactly accurate when it comes to the size of the coil, it infact consists of about 70 feet of wire wrapped around the housing. The impedance is high on this solenoid and as a result a sepcial pulse is required to drive it. Most Ion boards operate the solenoid by sending a surge of full power for a few milliseconds, afterwards the signal is pulsed on and off at a very fast rate. What this does is keep the armature in the firing position while using the lowest amount of battery power possible. This serves to both lengthen battery life, and keep heat buildup to a minimum. Ion solenoids are very durable and will last a VERY long time. Many were tested past one million realistic cycles prior to being released. The Ion solenoid has two disadvantages that I make note. The first is that the flow around the armature isn't the greatest, as a result of how the inside of the housing has to be shaped. It will allow air to vent but it only does it at nearly half the rate of traditional spool-based solenoids. A QEV valve is suggested as a result. Additionally, due to the small volume that vents per cycle, it is suggested that a solenoid like this be used mainly in a marker design with small solenoid output air volume. The small Ion solenoid will be able to handle a small volume or air very easily. The other disadvantage is that the entire housing is composed of a poured polymer casing which will hold pressure fine, however can be broken if forced. For instance, the output hose barb can easily be broke if the hose is too tight on it (this is probably the most common problem with the valve, but unfortunately can't be avoided. Ion solenoids are very inexpensive due to the simplistic design, making it useful for custom normally-open projects and tinkering. I use Ion solenoids in several prototype markers of my own.