The 500SE"s pneumatically balanced servo-valve is actually a two-stage valve. Just a small sip through the mouthpiece opens the servo mechanism or control valve lever. Air flow from the servo valve creates a vacuum which immediately opens the main valve diaphragm allowing air to flow through the regulator to the mouthpiece. Instead of one small port to provide air flow from the first stage, the 500SE features porting around the entire main valve. With less restriction from the first stage, this allows maximum performance. 500SE Second Stage Pneumatically balanced servo valve system Patented Orthodontic Mouthpiece for comfort and reduced jaw fatigue Standard with 30" maxflex hose Easily disassembled without the use of tools and underwater if necessary Left or right positioning - no upside down Boltsnap tie point DC7 First Stage High performance over-balanced first stage provides progressively greater intermediate pressure as depth and gas density increases for superior gas delivery under the most extreme conditions Fixed hose routing ideal for both backmount and sidemount configuration Environmental sealing prevents internal corrosion, contaminants, and icing of the first stage