This is a type of Honeywell Gas Valve, specifically a two-way, suspended, 1/2-inch, two-state, fast-open pneumatic gas valve. It is designed for modulating gas flow in various types of appliances, such as furnaces, generators, air conditioners, and boilers. The valve can be used with up to 28" W.C. of natural gas, and features fast-opening, temperature-independent control. It also has a polycarbonate diaphragm, providing sealing protection and a long service life.