No kit requires a purge valve...
The nitrous in the bottle is liquid, when it comes out turns to gas...if it sits in the line for a while it turns to liquid again.
The liquid is not harmful to your motor but no performance gain.
Purging it just sprays it out so you have fresh in the line.Also looks very cool.
I use the 5115 kit w/ 75 jets and 100 jets.
The basic kit is all you need.
A bottle warmer is nice($100)
a blanket is nice too($35) both you only need when it's colder than about 70* out.
Remote bottle opener would be very convenient
But kinda pricey($165??)
You keep your bottle open and have an electronic switch to open it to the selonoids.Get it...you will love it
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4.10's,long tubes & 75 shot...Goes 12.50's
Check it out at
http://www.burnouts.webprovider.com