Most of the operations share some similarity, but have several different key functions.
The Nelson valve was the first type of paintball gun ever built, originally designed by Crossman for the Nelson Paint Company, to provide a delivery system for their 'paint capsules', originally designed for marking things like trees and cattle. The first gun was the Nelspot 707, a metal, bolt-action gun working on the Nelson valve. Many different designs of Nelson valves have been produced, mostly pump-action guns, but a few semi-auto conversions existing as well.
The main design still using the Nelson valve is the popular CCI Phantom pump marker, however ATS markers use a semi-auto version of the Nelson valve. The old Brass Eagle Rainmakers also used a semi-auto version of the Nelson.
The Nelson valve operates by pumping the gun, which pushes the bolt back, connecting to the hammer and pulling both forward. When the sear is released, the hammer goes back, triggering the valve.
ATS Semi-Auto Nelson:
The Sheridan valve was introduced by Sheridan as a competitor to Nelson-valved guns. Plus, most modern guns are derivatves, in some sense, of the Sheridan valve. Everything from Tippmanns to Egos owe part of their design to the Sheridan.
The Sheridan is an innately simple design. Cocking the gun moves the bolt back and forth, allowing another ball into the breech, and pulls the hammer back. When the trigger is pulled, the hammer is pushed forward, opening the valve.
A Sheridan was also converted by Glen Palmer into the first ever semi-automatic marker, called Camille. It uses a pneumatic ram replacing a person manually cocking it. The design remains virtually unchanged in Palmer's Blazer, Hurricane and Typhoon markers, as well as the Autococker design. Currently, only WGP and PPS still make Sheridan designs. Sheridans are decently efficient, and extremely durable-there are thousands 10-year-of Sheridans still running today, mostly on original parts.
The Stacked-Tube Blowback was a derivative of the Sheridan valve. Instead of requiring an pneumatic ram to recock the the gun, it used a modified valve which both blew the ball out the gun and the ram back to recock it. The first was developed by Line SI, in the original Promaster. However, the original Promaster was never especially popular, leading to the common misconception of the PMI VM-68/PMI III being the first STBB. Currently, the stacked-tube blowback takes the form of Spyder, Brass Eagle and Piranha markers, among others, although it's remained virtually unchanged from the old VM-68. Stacked-tube blowbacks are cheap and simple, but not very efficient.
Staked-Tube Blowback diagram:
The inline blowback was developed by Tippmann, presumably as an extension of its' earlier, Nelson-based pumps. The Tippmann SMG-60 series has the honor of being the first non-pump marker, debuting in 1987. (However, the distinction of first gravity-fed semi is given to Glen Palmer's Camille, as the SMG-60 was only capable of full auto and required proprietary stripper clips, instead of a hopper). The SMG-60 was refined into the 68 Special in 1989, making it the first modern blowback, and almost the first true gravity-fed semi marker. The inline blowback is functionally identical to the stacked-tube blowback, with the only difference being that the bolt is placed in front of the valve, rather then above it. Like the stacked-tube blowback, it has changed very little in the now twenty-plus years it's existed. From the first 68 Special to a brand new Alpha Black, the internals are almost identical, the only change being a higer-flow valve introduced with the Model 98. Currently, Tippmann is the main producer of inline blowbacks, in the form of markers like the 98C, A-5 and X-7. However, Brass Eagle, Ben Tippmann, JT and others make similar designs. Inline blowbacks have high recoil and low efficiency, but are very simple and cheap design.
The Automag was originally developed by Tom Kaye, and, like the name suggests, is kind of the inverse of the blow-back design. It works by keeping air pressure behind the bolt, which push the bolt forward when the sear is tripped. A spring returns the bolt to the original position. However, the valve is very compact, and also has an integrated regulator, allowing it to still remain one of the most durable and effective design, around 2 decades after its original inception. Blow-Forward designs have very low recoil, and don't need an additional regulator, due to the reg integrated into the valve, but aren't as efficient as other designs.
Currently, only AGD, the original producer makes blow-forwards. However, Dye just introduced a new marker, the Proto SLG, that uses a design very similar to the Automag. Instead of a spring return, it uses pressure to recock the bolt as well.
Stacked-Tube Poppet Valve
The stacked-tube poppet was originally designed as an electropneumatic conversion for Spyders, originally developed by Bob Long. Long eventually went on to develop the Intimidator design, one of the current popular electropneumatics. The same design, with minor changes, is used by Egos, Cyborgs, Angels, Vikings, Promasters and others. Stacked-tube poppets are known for excellent efficiency, but higher recoil.
The only difference between poppets and the autococking Sheridan design is that, instead of using a hammer moved back and forth by a spring and a ram, the hammer is integrated into a device similar to a 2-way pneumatic ram, controlled by a 4-way solenoid.
Inline Spool/Balanced Spool
Balanced spool valves are derivatives of the blow-forward Automag design, which use pressure on both sides of the bolt instead of pressure and a spring to cycle the bolt. However, unlike the SLG, it uses a 4-way solenoid to reroute the air flow in front of and behind the bolt to cycle it. The design is used, with minor variations, in Dye/Proto Matrixes, Smart Parts Shockers, Ions, Vibes/SP-1s, ICD Freestyles and others. Inline spools are known for low recoil and noise, but lower efficiency.
Those cover the main designs (If I'm forgetting one, let me know, and I'll add it). However, there are a few designs that use major modifications of existing designs, or use a unique design.
The Mini uses a design similar to the poppet, with air cycling the bolt, however it has a substantially different layout.
The Epic essentially uses a mechanical version of the poppet design, but, instead of having a cycling bolt, it has a small trap door that blocks off the feedneck.
The C-3 is a very unique design. Instead of running on CO2 or HPA, it runs on propane. It gets 20,000 shots off of a standard camping propane bottle. It uses a piston moved by the pump to fill the chamber with propane, then, when fired, ignites the propane to propel the ball out. However, this effectively limits it to only a pump gun, since the gun simply gets too hot for a semi-automatic design.
I know there are several older derivative designs that I'm omitting. However, they're all out of production and, anybody who's buying them probably doesn't need this post.
This post has been edited by Marauder_Pilot: 13 April 2008 - 01:37 PM