Air Circuit Logic Without Power

Air Circuit Logic Without Power
(Last Updated On: September 19, 2020)

How do you get air circuit logic without power?  A small PLC (Programmable Logic Controller) like a PICO™ or a LOGO™ can provide low cost computer control to an electrical pneumatic circuit.

The problem is, what happens to these electrically driven logic devices and to the logic in your air circuit if there is no power supply? In other words, when the power fails.

Long before PLC  technology became widespread and inexpensive, air circuit logic without power was available through air logic devices, resulting in the ability to build an air circuit logic without power.

The devices that enable a circuit builder to put together a simple, or sometimes quite complex air circuit,  are easily integrated into an air logic circuit resulting in an air circuit that can run a number of compressed air devices in sequence, all without and electrical signal input of any kind.

Air Circuit Logic Without Power Is Safe!

With the inherent benefit of safety and simplicity, air logic components these OR gates, AND gates, NOT gates and PULSE valves allowed designers to build sometimes quite complex circuits that were started, cycled, controlled and stopped all with control air signals generated electrically with a PLC.


Compressed air logic device - an and gate
This is the schematic for an AND gate. When a control air signal is present at both A & B ports, an outgoing signal is generated at port Q.


One issue with using air logic to build an air circuit is that the control air – the compressed air flowing through the various pneumatic logic devices – has to be clean and dry. This may require the inclusion of additional compressed air treatment to ensure that the logic devices continue to run reliably. This does add cost to the building of an air logic circuit, yet the results can yield benefits far outweighing the cost of treating compressed air to make it better quality.

Other available air logic devices include:

  • OR gates (either input equals an output)
  • NOT gates (absence of a control input creates output)
  • Flip Flop (each input results in an output to one of two ports)
  • Delay
  • Pulse
  • Two-Hand Ant-Tie-Down
  • Oscillating output (like a flip flop but continuous operation)
  • Timers
  • Counters

… among others.

Next time you are working on a simple circuit, consider avoiding the use of electricity completely, and design your circuit to run with compressed air only.

Need a little help with some air logic for your compressed air circuit?

Hello, I am Bill, the Compressed-Air-Man. I have years of experience in industrial and residential compressed air applications, air compressors and general pneumatics. I created this site to help professionals, students, and DIYers understand and properly implement and maintain compress3ed air systems.


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