From: Zex website
Q: Do I need a purge kit?
A: A nitrous purge kit clears the delivery lines of unwanted air and vapor and guarantees immediate power from your nitrous system. It’s also used to intimidate your competition and shows the world your nitrous equipped. The ZEX™ purge kit (part #82010) uses the industry’s largest solenoid, creating an awesome purge cloud.
Wiki-
The purpose of a nitrous purge is to ensure that the correct amount of nitrous oxide is delivered the moment the system is activated—air or gaseous nitrous oxide in the line will cause the car to "bog" for an instant until liquid nitrous oxide reaches the intake.
Q: Do I need a purge kit?
A: A nitrous purge kit clears the delivery lines of unwanted air and vapor and guarantees immediate power from your nitrous system. It’s also used to intimidate your competition and shows the world your nitrous equipped. The ZEX™ purge kit (part #82010) uses the industry’s largest solenoid, creating an awesome purge cloud.
Wiki-
The purpose of a nitrous purge is to ensure that the correct amount of nitrous oxide is delivered the moment the system is activated—air or gaseous nitrous oxide in the line will cause the car to "bog" for an instant until liquid nitrous oxide reaches the intake.