A gas control valve can be found on any appliance that utilizes gas. These valves are vital for the operation and safety of any gas appliance. The valve does exactly what it sounds like, it controls the amount of gas flowing to create a steady flow without allowing any gas to leak. The most common gas appliance found in US homes is the hot water heater, although the valve serves the same purpose for heating systems and stoves as well. If you need to know the specifics, here is a brief overview detailing how the control valve functions.
A gas burner sits underneath the appliance and heats the gas that is supplied. The control valve regulates the pressure and the amount of gas that is supplied to the unit. The pressure is important. Too much pressure could result in fires or explosions. Too little pressure will not allow the proper amount of gas to be ignited for the appliance to operate.
Another function of the control valve is to sense whether the gas is being heated or not. As the gas passes over the pilot light, the gas is ignited. This creates a higher temperature. If the temperature is not reached, the valve will cut off the supply. This prevents potentially deadly gas from sitting around and escaping in to the environment.