Skirt seals, until now, have not had this feature, and I really wished that I had it when I was playing with my PAC shooting marshmallows, and on occasion sucking gooey blobs into the plunger tube. Fortunately, they were surprisingly easy to get out (probably thanks to the lube), but I didn't feel like I could consider a blaster to be complete if it had problems associated with plunger vacuum, even if they were only an issue on occasion. I found the solution on the head of the pump for the Buzzbee Big Blast. The check-skirt is based on that design, but with a skirt instead of an O-ring.
How to build it: Seriously, look at the diagram. And look at what I did-- I used a saw, drill, and hammer to make this, although later versions will probably be milled for a nicer finish (The PVC is actually cracked in one spot from where I tried to use an oversize drill as a countersink, and I had to remove a piece of the CPVC because it bent inwards during assembly).
Why it's good to have:
No misfires due to vacuum in the plunger tube
No darts or debris gets sucked into the plunger tube
Slightly easier draw
Why it's not necessary to have:
Air can usually get around the dart prior to firing the hopper
A nail or screw will prevent darts from sucking back into the plunger tube (usually)
Misfires due to vacuum in the plunger tube are rare under normal circumstances.
Edited by KaneTheMediocre, 19 November 2010 - 07:05 PM.