Solenoid Tech - Types
All solenoids used in any industry will fall into one of two possible categories: indirect-acting or direct-acting. These terms are used to describe the role of the electromagnet inside the valve, and specifically what it does to the "load" which is typically the directional valve portion of the system.
Direct-Acting Soleniods:
The first type of solenoid is called a direct-acting solenoid, also known as a self-actuated solenoid. These are very simple in design and consist mainly of a solenoid (electromagnet) and an armature or plunger inside it (the magnetic moving component). Industries outside of paintball use these types of valves heavily, an example being the starter solenoid in a motor vehicle.
The magnets in are usually stronger since they need to physically move a heavier load. As a result, they require more power to activate (and also tend to experience higher electrical resistance and can build up excess heat). In the paintball industry, all "sear-tripper" electronic markers use direct-acting solenoids (Tippmann E-grip, electronic Spyders, electric Piranhas, E/X-Mag, others). In that application, the solenoid assembly consists of the solenoid armature attached to the sear, which is physically pulled or pushed when the solenoid energizes.
One sub-division of direct-acting solenoids is their ability to control pneumatic valves. This is accomplished by connecting the end of the solenoid armature to a small pneumatic directional spool.
The purpose of the spool is to take in air pressure and release it through an output port when required to do so. There are many different applications of this, but most valves will have two separate outputs available (one for idle output, and the other for energized output). When energized, the spool valve switches positions to redirect airflow around it.
Indirect-Acting Solenoids:
Indirect-acting solenoids are much more complex and take much more time to explain. Essentially, an indirect-acting valve consists of two pressure valves integrated into one assembly. The main valve is the spool, which works the same way as described above (a slideable valve that releases air when the solenoid is energized), however indirect solenoids also use a second mechanism called the pilot valve, that is located between the spool and the electromagnet. The pilot is basically a small direct-acting valve, which activates an air piston to push the large spool.
The pilot valve is actuated by a tiny direct-acting solenoid, but the presence of a pilot turns the whole system into an indirect-acting valve. This is because the tiny solenoid core is used to actuate a larger load (spool). The determining factor is how the electromagnet interacts with the load: direct-acting solenoids use the magnet itself to move the load since they are physically connected, or since they're physically the same component (such as an Ion solenoid). Indirect-acting solenoids use the pilot valve to control the main load (spool).
The reason indirect-acting solenoids exist is because a lot of power is required to move the armature/spool in a direct-acting valve. In an indirect-acting solenoid, the pilot valve uses a very small amount of air pressure (a very small load) to physically move the large main load. In essence, the electromagnet is allowed to be much smaller in size, and what it lacks in physical size it makes up with air pressure force. The same load can be moved using either solenoid type, however in most cases the direct-acting solenoid will require MUCH more power than the indirect-acting version. For example, the small magnetic coil in an indirect-acting solenoid might require half a watt of power, whereas a direct-acting solenoid moving the same load might have a resistance of over 4 watts; the difference between them is several times as much power from one to the other. This can often be noticed visually since direct-acting solenoids require the use of larger capacitors on the circuit boards controlling them (whereas some indirect valves can utilize as little as 3 volts with no capacitor). Therefore, the use of the pilot valve makes indirect-acting solenoids much more power-efficient, however they add additional moving parts and potentially-fallible components to the assembly.
Solenoid Valve, Pressure Output:
The description for how sear-tripper solenoids function is essentially finished. There isn't much to them outside of what was stated at the top of this page, before the introduction of indirect-acting solenoids. The rest of the descriptions deal more heavily with pneumatic valves (direct and indirect) and how they work.
Accordingly, the next level of classification involves how many pressure input and outputs are present in that particular spool valve. All pneumatic solenoids have at least one input and at least one output. Each output port must also have one exhaust port to function as well, however some have dual outputs/exhausts which alternate open and closed. There's another type known as double-action solenoids, which push the spool open then push it back closed again, but they're not used in paintball so I don't explain them.
There are three main types of spool valves used in paintball, described here. Of them include the four-way (two outputs, two exhausts) and the three-way (one output, one exhaust).
· Four-way spool valve: this valve type is commonly used in fully-electropneumatic markers, where air pressure is used to push a piston forward, then used to push it backward after firing. Four-way valves have two outputs so there are two ports through which air can travel (either one or the other, depending on the spool position). The important thing about this is that air is always being released through the output, the question is rather which of the outputs. During firing, one of the outputs is closed off and pressure exits the other output, then the outputs switch back after firing is complete. Some markers that use this type of solenoid include an Ego, Angel, Impulse, Shocker, Matrix, etc. The incorrectly-worded "three-way valve" on Autocockers is also an example of a four-way piston.
· Three-way spool, normally closed (NC): these are three-way valves that only output pressure when energized. While these solenoids are idle, they don't output any pressure. Example markers using this design include older Bushmasters, pVI Shockers and Shocker Sports, AFSP (air-forward, spring-return) aka FASOR (forward-air, spring-operated return), Invert Mini, and some others.
· Three-way spool, normally open (NO): these are three-way valves that output pressure continuously while idle, and shut off airflow to fire the marker when they become energized. Example markers using this type of solenoid includes Ions, Freestyles, mQ valves, and scarce other designs.
The pilot valve in a solenoid is always a three-way normally-closed. When the solenoid is energized, the pilot is opened and it releases air to push upon the spool. The spool valve can be either three-way or four-way. Typically, three-way solenoids are smaller in size since there's physically less room required for air passages and seals on the spool valve itself. I should also mention that any four-way solenoid can be effectively converted to a three-way, by simply blocking off one of the outputs (blocking the idle output makes it a normally-closed; blocking the firing output makes it a normally-open).
Solenoid Layout & Design:
Each indirect-acting valve, regardless of the make or manufacturer, can be divided into three sections: coil, pilot, and spool (sometimes known as the plunger, sleeve, and piston respectively). The coil is the actual electromagnet part of the whole assembly, and consists of a conductive copper wire wrapped around a metallic housing, inside of which sits the core which is the opposite magnetic component in the valve. The core is made from steel and is fitted with a spring on the end (indirect-acting valve only).
Located on the opposite end of the solenoid assembly is the spool, which is the piston-based part of the assembly, and the main moving part. Spools are generally made from brass or aluminum, depending on the manufacturer. The spool is also fitted with various seals which are used to direct airflow around the spool within its housing (into the housing, around the spool, and back out). Sometimes the seals involved are part of the housing instead of seals on the spool itself, but the function is the same. The spool housing is always machined from metal (most companies selected aluminum for this).
The final part of the solenoid, the pilot, is the physical connection between the movement of the core and the consequent movement of the spool. The main component for the pilot is a circular piston which is what actuates the spool to the open position. This is a small plastic disk fitted with an o-ring around it. Behind the piston a small actuator can be found, a component to hold the actuator in position, and a sealing plug housed within the actuator (there’s also a spring in there). Most of these components are made from polymer to facilitate gliding and sealing, such as rulon, nylon, polysuphone, or similar. The actuator plug is made from synthetic rubber like other Buna or Nitrile seals. Some solenoids (such as Humphrey CRCB series valves) use a smaller-sized piston on the closing side of the spool, which is used to push it shut after de-energizing. This is made from the same material as the main pilot valve.
Direct-acting solenoids can be designed a few different ways. The more traditional design involves a core and spool similar to the indirect-acting valves, however the difference is they're directly linked so the movement of the core is what moves the spool. This is common but the power requirements of these valves are very high. The other design method involves anything without a balanced spool-shaped valve, where the core actually acts as the air valve itself (it’s technically not a "spool" but you could call it that for simplicity). These solenoid types are usually made specifically for one marker in particular (for instance, Ion). The page explaining how individual solenoid brands function will shed light on this.