3/2 Directional Control Valves Pneumatic System

A 3/2-way valve has three channels and two switch positions. It is particularly suitable for controlling single-action cylinders. The compressed air feed is usually closed in the rest position but exhaust can escape from the cylinder at that time. This type of cylinder is operated from one side only (usually by electromagnetic means in an electropneumatic control system) and has a spring-operated return. The graphic below shows the schematic symbol for such a valve.


The following graphic illustrates how the cylinder and valve interact (the example shows a monostable valve). When the solenoid valve is actuated (a), compressed air (dark blue) from inlet 1 is channelled to outlet 2 where it enters the single-acting cylinder. The cylinder thus extends, i.e. the piston moves to the right. 

If the coil turns off, the return spring restores the valve to its rest position (b). The compressed air inlet 1 is now closed but channels 2 and 3 are linked togetherso that the exhaust from the cylinder can escape through them (light blue). The piston thus retracts again, i.e. it moves to the left.


The following animation once again illustrates the extension and retraction of a cylinder by means of a 3/2-way directional control valve.



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