A unique combination of a valve and a 1st stage in a very light package A combination 1st stage and tank valve perfect for pony bottles. The Envoy RaZor regulator has a Flow-by Piston style 1st stage with design features that allow direct airflow through the 1st stage, providing performance that far exceeds what would be expected in an economical regulator. The 2nd stage is a balanced orifice design. The Flow-by Piston design of the RaZor 1st stage provides much greater reliability and serviceabilty compared to conventional designs, while improving responsiveness and performance at all breathing rates. This 1st Stage sits direct atop a Tank Valve section the threads into any standard 3/4-14 NPSM Scuba Cylinder. This combination saves space and increases efficiency making it ideal where weight and space are critical such as stage bottles and fully redundant systems. The RaZor comes with a filling adapter that allows the RaZor to fill its tank using a standard Yoke Filling Whip. You can also purchase a Yoke Transfiller that will allow you to fill the RaZor 1st stage off of another SCUBA cylinder. Look below to view an instructional video on how this is done. Work of breathing at heavy demand*: 1.34 Joule/Liter *198 (60M) depth 750 psi inlet, 62.5 RMV (liters per minute respiratory volume) Like all Zeagle regulators, The Envoy RaZor comes factory ready for use with EAN/ NITROX to 40% O2.