Valves 101

Part II - Spool Valves

The recently introduced ‘Spool Valve’ firing platform in its many variations and adaptations is rapidly overtaking the marker market -- from the entry-level Smart Parts Ion, to Dye’s DM4/5/6/C line of superguns. Though calling this design a “recent” development may seem a little overstated for one that has been around since 2000, it’s a big departure from the ubiquitous spring/hammer/valve combos that ruled this for nearly 2 decades prior. Due to the many existing and developing variations of the spool valve design, this article will mainly focus on the traditional concept as it’s now employed in Dye’s FUSE bolt.

Initially developed for Diablo’s Matrix marker, early versions of spool valve markers featured large, cumbersome bolt systems that had enough parts and o-ring seals to make even a seasoned airsmith’s head spin. You can see the original design here <link coming>. Luckily for us, in late 2002, Dye purchased the exclusive rights to the spool valve design and managed to streamline the entire package. The result was the first FUSE bolt shipped with Dye’s DM4 in 2004: an elegant assembly of just four parts (1 moving and 3 static) that was capable of spitting out 20+ balls per second with ease.

The overarching design criterion revolves around using the bolt to not only chamber and seal a paintball in the breech, but to also use the bolt as the primary air-release mechanism (a function previously reserved for a bolt, hammer, and knock-open valve trio in most other designs).

The basic concept at work is rather simple: a fixed-volume reservoir fills with firing gas at a regulated pressure. At the instant the firing cycle begins, the input to the reservoir is sealed-off, thereby preserving the theoretically consistent, fixed volume of pressurized air that will be used to propel the paintball. Once the reservoir is sealed, the “flood gates” begin to open—venting the reserved air into the breech to fire the chambered paintball. The valve then resets itself in the reverse order: closing the vent then opening the input to once again fill the reservoir with regulated air for the next shot.

Because the spool valve makes use of a theoretically constant and fixed volume of air to fire each paintball, the design has a number of benefits over other “traditional” designs. First, because the bolt-cycling energy (translate: LPR pressure) is not required to knock-open a sprung and pressurized valve poppet (a la Intimidator, Angel, Ego, etc.), spool valves are typically considered to be “softer” on paint. Bolt LPR pressure in a FUSE bolt, which is mostly governed by what it takes to overcome the static/dynamic friction of the o-ring seals, can run as low as 30-35psi—this is significantly lower that the ever-popular Intimidator or Ego, which can run as high as 70 or 90+psi, respectively (translate: Chop! Chop! Chop!). Additionally, valve dwell in a spool design—that is, how long the valve remains open/”venting”—is merely determined by the minimum amount of time it takes for the valve’s reservoir to empty; any amount of dwell beyond that is moot (sorry for all those who have gotten used to their dwell-ramping Timmies). Thus, what I’m trying to explain here is that you end up with an overall firing cycle that is governed by fewer variables and, in this case, simplicity certainly translates to consistency and reliability.

Of course, with every upside there is a downside. Because the spool valve assembly incorporates a number of o-rings throughout its design, spool valve markers can be more prone to leaks, “bolt stick” (where excessive friction in the seals prevents complete cycling), and first shot drop-off. As such, regular maintenance—especially following heavy use or in “dirty” conditions—is a very good idea to ensure consistent, reliable operation. Spool valve markers have also gained an infamous reputation for being “gas hogs.” While recent valve iterations have improved on its predecessor’s shortcomings, exact reasons for this air inefficiency currently elude this author (though may hopefully be soon uncovered in an investigation and review by Alchemy’s team of mad scientists).

As you can see, the valve is an extremely versatile addition to an otherwise “been there, done that” technology. With a firm presence in both the low- and high-end marker markets (and rumored current development by a legendary name in Paintball), the design will inevitably continue to flourish for quite some time to come.