The low-profile compact Xstream second stage uses pilot-operated upstream demand valve technology that also seals the seat without the use of conventional knife edge design seating systems. This servo-assist feature allows for very low inhalation effort and also eliminates any need for a venturi switch or adjustment knob. The second stage is also ambidextrous, allowing both left and right hose routing and breathes equally well in nearly any swimming position while the side mounted exhaust directs the bubbles out of the field of vision.