Spool valve markers are unique in that they typically have only one moving part (the bolt) which simultaneously acts as both the firing valve and the bolt to close the feedneck. other types of markers have a separate bolt and valve, which has been simplified into one moving stroke with spool-based markers.

There are many types of spool valve markers but they can all be categorized based on their layout. For the purposes of this website I categorize them as Matrix-based (dump chamber in rear) or Shocker-based (dump chamber in front). This is not an official designation, but I believe it to do an adequate job since there are only two main designs, and Matrices/Shockers were the first of each.

Unbalanced (Blowforward); Mechanical:

Automag

Automag

Automag

Automag L10

Automag RT (wmv)

E-Mag

RT E-Mag

Pneumag

Level-10 bolt

This design includes the Automag (pictured above), Desert Fox, Tiberius series markers, as well as a few others. Automag RT (wmv) animation from AGD. These function by shutting off inlet to the dump chamber, while at the same time releasing the bolt which then fires once it reaches forward. The bolt is returned by a spring, thus it is held in the "open" position if no pressure is applied.
The bottom row of animations are as follows: (1) RT E-Mag without the RT animated; (2) Full RT E-Mag; (3) Pneumag modification without RT; (4) Level-10 low-impact bolt. Click for a slower E-Mag, RT E-Mag, or Pneumag animation.

Unbalanced (Blowforward), electropneumatic:

Freestyle

Rail

Ion

Ion

Ion Full

Ion Nano bolt

Ion QEV

Threshold

G4 stock bolt

G4 TechT bolt

These markers use a bolt that is "held back" in the open position, then allowed to move forward to fire. Freestyles are similar in layout to Automags; Ions and Rails are laid out similar to the original (balanced) Matrix design. Ion bolts without tails (Nano, L7) can be thought of as inverted Automag/Freestyle bolts.
The last type of bolt layout shown is the guide version, shown in the third row. These bolts are hollow and ride on a central guide or stem. These are examples of the balanced Shocker design made into a three-way blowforward, other markers using this layout include the Droid, Pikkadoll, Ion Hollowpoint bolt, Proto SLG, and Eclipse Geo.
Click for a slower Rail animation. The last animation is of the Ion with and without a QEV. The movement of the bolt in that animation is perfectly accurate, down to the millisecond. Click for a slower Ion QEV animation.

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Balanced, Matrix-based:

Pre-DM Matrix

Pre-DM Matrix

Matrix Slambolt

Dye DM4/5/6/C/+

Droid

Matricies use a balanced bolt with the piston in front and the dump chamber in rear. The bolt is pushed forward to release pressure and fire the ball.
I use the term "pre-DM" to refer to the Matrix design before the DM4+ in 2004. The firing assembly is the same; the rest of the marker is different. DM animation from Subvertz and Excel-Krusher. Click for a slower pre-DM Matrix or DM4 animation.
The last animation is for the MacDev Droid, which fires using a nearly-balanced four-way bolt, also operating a shutoff shuttle valve behind it. The layout of components pushed me to classify this as a derivative of Matricies, however the bolt riding on a central guide lends it some similarities with Shockers too.

Balanced, Shocker-based:

SFT Stock bolt

HE bolt/NXT stock

Evolve bolt

FEP Quest

Air Challenger 264

Shockers use a balanced bolt with the dump chamber in front and the piston in rear. The bolt is pushed forward to release pressure and fire the ball. Click for a slower Shocker animation: stock bolt; Evolve bolt; HE bolt.
Quests function the same as HE Shockers except the dump chamber has been moved to the inside of the bolt instead of around it (and some other rearranged parts).
The Air Challenger marker shown above (the name of which is unknown) is similar to an HE Shocker. Click for slower AC 264 animation.

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Spool valve, balanced, dual-piston:

Omega-II

This marker is similar to the Shocker design, however uses two separate spool components to function. Interestingly, the creator of this marker is also the creator of the original Matrix/Omega, so one can wonder if this was designed to be a Matrix predacessor. I don't know its actual name being as it was never commercially marketed. Click for slower animation.