The ADV Adjustable piston valves are designed to be used for precise setting of gas or air flow rates in combustion systems. This valve can be adjusted sensitively and accurately with a screwdriver. Turning the screw counterclockwise and clockwise increases and decreases flow respectively. A cap conceals the adjustment and discourages tampering with setting. These valves are not designed for shutting off gas; you may use approved plug (ball) valves or cock for this purpose. These valves are also couplable with servomotors so-called ADVR model.