Introduction to Pneumatics
Pneumatics Symbols
Air generation and distribution
Table 1: Symbols use in energy conversion and preparation
ITEM / SYMBOL / MEANINGSUPPLY / / Compressor
/ Pressure Source
/ Pneumatic Pressure Source
/ Air Reservoir
SERVICE EQUIPMENT / / Filter : separation and filtration of particles
/ Filter and separator (automatic)
/ Lubricator
/ Pressure regulator
COMBINED SYMBOLS / / Air Service Unit : Filter, Regulator, Gauge, Lubricator
/ Simplified air service unit with lubricator
Input Elements
Directional control valves
Table 2: Directional Control Valve Symbol Development
Explanation Of Symbol / Symbol DevelopmentValve switching positions are represented as squares /
The number of squares shows how many switching positions the valve has /
Line indicate flow paths, arrows shows the direction of flow /
Shut off positions are identified in the boxes by lines drawn at right angles /
The connections ( inlet and outlet ports ) are shown by lines on the outside of the box /
Table 3: Directional Control Valve, Ports and Positions (ways)
SYMBOL / EXPLANATION/ 2/2 - way directional control valve, normally open
/ 3/2 – way directional control valve normally closed
/ 3/2 – way directional control valve, normally open
/ 4/2 – way directional control valve
Flow from 1 to 2 and from 4 to 3
/ 5/2 – way directional control valve
Flow from 1 to 2 and 4 to 5
/ 5/3 – way directional control valve
Mid position closed
Flow Control Valve
Table 4: Flow Control Valves
SYMBOL / EXPLANATION/ Flow control valve, adjustable
/ One-way flow control valve
Pressure control valves
Table 5: Pressure Valve
SYMBOL / EXPLANATION/ Sequence valve-in line
/ Adjustable pressure regulating valve, relieving type
Auxiliary Symbols
Table 6: Auxiliary Symbol
SYMBOL / EXPLANATION/ Pressure gauge
/ Silencer
/ Exhaust
/ Plug
/ Visual indicator
Processing Elements
Table 7: Non-return valves and derivatives
SYMBOL / EXPLANATION/ Check valve
/ Shuttle valve
/ AND Valve
/ Quick exhaust valve
Actuator (Output)
Table 8: Actuators
SYMBOL / EXPLANATION/ Single acting cylinder with spring return
/ Double acting cylinder
/ Double acting cylinder with double ended piston rod
/ Double acting 2 cushion cylinder
/ Air motor rotation in one direction
/ Rotary actuator
Development of single actuator circuit
Example 1:Direct control of a single-acting cylinder
A single acting cylinder of 25mm diameter is to advance a component when a push button is pressed. As long as the push button is activated the cylinder is to remain in the clamped position. If the push button released, the clamp is to retract.
Example 2:Indirect control of a double acting cylinder
A double acting cylinder is to extend when a push button is operated. Upon release of the push button the cylinder is to retract.
Figure 4: Circuit Diagram
Example 3:The logic AND function
The piston rod of a double acting cylinder is to advance when both push button of the 3/2 way valve is actuated. If either of these is released, then the cylinder is to return to the initial position.
Example 4:The logic OR function
A double-acting cylinder is to advance if one of two push buttons is operated. If the push button is then released, the cylinder is to retract.
Example 5:Memory circuit and speed control of a cylinder
The piston rod of a double acting cylinder is to advance when a 3/2 way push button valve is actuated manually. The cylinder is to remain advanced until a second valve is actuated. The signal of the second valve can only take effect after the first valve has been released . The cylinder is to then return to the initial position. Then cylinder is to remain in the initial position until a new start signal is given. The speed of the cylinder is to be adjustable in both directions.
Figure 7: Circuit Diagram
Combinational valves
The combined functions of various elements can produce a new function. The new component can be constructed by the combination of individual elements or manufactured in a combined configuration to reduce size and complexity. An example is the timer which is the combination of a one way flow control valve, a reservoir and a 3/2 way directional control valve.
Figure 8: Time delay valve
Example 1:The timer delay valve
A double-acting cylinder is used to press together glued component. Upon operation of a push button, the clamping cylinder extends. Once the fully advanced position is reached, the cylinder is to remain a time of T= 6 seconds and then immediately retract to the initial position. The cylinder retraction is to be adjustable. A new start cycle is only possible after the cylinder has fully retracted.
Figure 9: Circuit Diagram
Development of multiple actuators circuits
In case of multiple cylinder circuits, a clear definition of the problem is important. The representation of the desired motion of all actuators described using the displacement-step diagram. The special condition for the start of the sequence must also be defined.
Example 1:Coordinated motion
Two cylinders are used to transfer parts from a magazine onto a chute. When a push button is pressed, the first cylinder extends, pushing part from the magazine and positions it in preparation for transfer by the second cylinder onto the out feed chute. Once the part is transfer, the first cylinder retracts, followed by the second. Confirmation of all extended and retracted positions are required.
Figure 10: Displacement Step Diagram
Figure 11: Circuit Diagram