The Vibe/SP1 solenoid is a direct noid, that is, it uses the battery power directly to open the main valve. This allows for a very economical solenoid.
In most guns, the solenoid used is piloted, which has a very small pilot valve that is opened by the battery, which then switches some air to drive the main spool of the solenoid. So it uses less battery power and a small amount of air assist to open. These are rather expensive and would not allow the Vibe/SP1 to be priced where they are.
Open Source Hardware