A pneumatic circuit is an interconnected set of components that convert compressed gas (usually air) into mechanical work. In the normal sense of the term, the circuit must include a compressor or compressor-fed tank. Components The circuit comprises the following components: Active components Compressor Transmission lines Air tank Pneumatic hoses Open atmosphere (for returning the spent gas to the compressor) Valves Passive components Pneumatic cylinders Service Unit FRL - Filter Regulator and Lubricator Pneumatic cylinder In general, based on the application, a pneumatic cylinder is usually a single acting cylinder, where there is a single port in the cylinder and where cylinder extension is done by compressed air and retraction by means of open coiled spring. In double acting cylinders two ports both extend and retract by means of compressed air. Direction control valve (DCV) The direction control valve is used to control the direction of flow of compressed air. Usually classified into normally open (NO)and normally closed (NC)valves. The normally open valves will permit flow from inlet port of valve to outlet port normally the flow will be cut by changing the position of the valve. The normally closed valves will not permit flow from inlet port of valve to outlet port normally the flow will be permitted only by changing the position of the valve. In general valves are designated as 2/2 DCV, 3/2DCV, 5/2 DCV,5/3 DCV etc. In which the first numerical indicates number of ports and second numerical indicates number of positions. To change the position, the valves are generally actuated by: Pedal Operated Push button operated Spring operated Solenoid operated By using Pneumatic source itself etc. The other auxiliary valves are Two pressure valve (And Valve) Generally two valve actuators (push buttons) are used when both the push buttons are pressed at a time the air flow takes place if either any one is pressed at a time air flow will not take place in valve outlet. Generally used in mechanical press and machine tools to ensure operator's both the hands are outside the machine or press during operation. OR Valve Generally two valve actuators (push buttons) are used when either one push button is pressed the air flow takes place. This is also called a shuttle valve. Check valve The check valve allows air flow in one direction, it is also called as non return valve. Quick exhaust valve The valve construction is OR