piston valve comparison
So now that you know how piston valves work you may be wondering what the difference is between the different types. While there are some performance differences, the primary reason for choosing one type over the other should be based on what configuration you desire. Why don't the performance differences matter much? Well because most piston valves are really fast regardless of the type and it isn't worth changing your design around completely to get it really really fast. In most guns the projectile has only moved a few inches before the valve is fully open no matter which piston type is used.
If you are using a light projectile and a short barrel then the relative opening times of the different types of valves may start to matter. Since coaxial valves are just a different configuration of barrel sealing valves we will ignore them for now. If the area of your piston seat is more than half of the area of your piston then a barrel sealing configuration is going to be faster than a chamber sealing valve. If the area of the seat is less than half of the area of the piston then a chamber sealing configuration is going to be faster, however if this is the case then your piston is probably bigger than it needs to be and you're just wasting pilot volume. To put things another way as your seat diameter to piston diameter ratio approaches unity (one) a barrel sealing configuration becomes faster while a chamber sealing configuration becomes slower (and more prone to bouncing). As the ratio approaches zero the opposite is true. For this reason a barrel sealing configuration is typically used for a fast, high flow valve. Barrel sealing valves are also easier to construct because they don't require o-rings.
related linkscoaxial piston valve
chamber sealing piston valve
barrel sealing piston valve
advanced piston valve considerations