Thermostatic operator consists of a saturated vapor charged bellows and a setting dial. Dial is set to the position equal to desired temperature. Balanced pressures between the adjustment spring and the bellows ensure a smooth and modulating operation of the valve (valves sold separately). Valve mounted operators provide fast acting modulating control of the space temperature through a vapor charge, ensuring the highest level of comfort control. Standard Valve Mounted Operators include a theft protection device and a snap-action mechanism that allows easy installation and removal without the use of tools. Conforms to ASHRAE/ANSI standard 102-1983.