The definition of a pneumatic valve is a device that is used to control the flow of air. It is commonly used in industrial settings, such as factories and plants, to control the flow of air to machines and other equipment. The valve is typically composed of two main components: a valve body and a valve stem. The valve body usually consists of two chambers, one to contain the air inlet and the other to contain the air outlet. The valve stem is usually connected to a pressure regulator, which controls the pressure of the air flowing through the valve. When the pressure regulator is adjusted, the valve opens or closes, depending on the pressure. Pneumatic valves can be used to regulate the flow of air in a variety of ways, such as controlling the speed of a machine or controlling the pressure of the air entering a device. They can also be used to control the temperature of air, or to control the flow of a gas or liquid.