Use a nitrous bottle regulator by Wilburn Motorsports
Wilburn is on this site.
The Pressure Pro is adjustable from 500-1100psi and is accurate down to 1psi. With a Pressure Pro you will no longer have to "purge down" to your desired bottle pressure. The Pressure Pro eliminates excessive purging keeping more nitrous in your bottle for better performance and your outlet pressure deadly consistent for accurate tuning. The Pressure Pro works on any nitrous system, wet or dry. There are two Pressure Pros available, the original Pressure Pro flows 125hp @ 900 psi, features 1/8npt inlet and outlets and is gauge ported. The Pressure Pro II flows 500hp @ 900 psi, features 1/4npt inlet and outlet and is also gauge ported. Both regulators feature a lifetime warranty against faulty workmanship and premature wear.