Pneumatic Components and Symbols

Pneumatic symbols are used to describe the function of the various valves and other devices which are connected together to form circuits and sub circuits.

Pneumatically controlled devices use pneumatic valves to control and direct the air and enable operations such as lifting, moving, pressing, etc.

Symbols for valves are shown as boxes representing the dfferent operating positions - the symbol shown for example is based on two boxes so it is a two position, or 2-stage, valve. Looking at any one of the boxes gives an indication of the number of ports on the valve - in this case there are 2 ports in each box (i.e. at centre top and bottom) so it would be a 2-port, 2-stage valve (2/2 Valve).

In the left-hand box, the arrow indicates that both ports are open and air would be allowed to pass through the valve in this position. In the right-hand box, the same two ports are shown as blocked. In this position, air is not allowed to pass.

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Component		Name and Description			Symbol
	Compressor	The symbol shown is that for the Main Air Supply which is normally supplied by a compressor. High pressure air can be produced using piston, screw or vane compressors.
	Receiver	The air produced by the compressor is stored in a vessel called the receiver or reservoir. The function of the receiver is to store the air for future use, to smooth uneven pressure and to allow water to fall out of the air to the bottom of the tank where it can be drained.
	Filter	Filters are used to remove small particles from the air which, if allowed to remain, would block small ports and jam spools etc.
	Air Bleed	This is simply an open pipe that allows the air in the circuit to escape once pressure is reduced by a diaphragm valve.
		Air Pipes Connected	The air produced by the compressor is distributed by air lines or pipe-work to the points where it is required.
		Air Pipes Not Connected	In a factory the pipe-work is run downhill in a further attempt to remove excess water from the system.
	Pilot Air	Pilot signals can be used to monitor the output pressure of a valve for example and supply a pressure which acts against a regulator spring to set the working pressure or to operate the spool inside a 5 port valve.
	Single-acting Cylinder	Pneumatic cylinders are more accurately termed linear actuators.In a single-acting cylinder compressed air is used to push the piston out (outstroke), and a spring to return it (instroke). When compressed air is supplied to the cylinder, the piston rod extends. A single-acting cylinder is normally controlled by a three-port valve.
	Double-acting Cylinder	Double-acting cylinders use compressed air for the outstroke and also for the instroke by reversing the air flow direction which is achieved using a five-port valve. They can produce bigger forces and are used more than single-acting cylnders. They can be used for both pushing and pulling.
	3-2 Valve	This valve shows 3 ports in each box and 2 boxes to indicate it has 2 stages of operation - hence 3-2 Valve. Single-acting cylinders are normally controlled by three-port valves
	5-2 Valve	This valve shows 5 ports in each box and 2 boxes to indicate it has 2 stages of operation - hence 5-2 Valve. Double-acting cylinders are normally controlled by a 5-port valve which is operated by Pilot Air signals from two three-port valves causing a spool inside the valve to move to one side or the other.
	Exhaust	The symbol shown is used to indicate when compressed air is released to the atmosphere - e.g. following the operation of a valve.
	Unidirectional Flow Control	###
	Shuttle Valve	###
	AND Valve	###
	Solenoid Activator	###