# Logic valves

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## Logic valves within the control circuit

The signal processing in the pneumatics takes place within the control circuit via logic valves. In this case, any complex logic function can be installed using the three basic logic functions "- OR - AND - NOT".

Pneumatic Logic Valves

### Logic AND-valve or two pressure valve

pneumatics two pressure valve

At the output of logic circuit, the operating pressure will only be connected through when both inputs are supplied with pressure.

With different input pressure, the side with the higher pressure closes the valve and the side with the lower pressure is directed to the output. This switching remains also when the both inputs get now the same high pressure.

Pneumatics- Two Pressure Valve or logic AND valve - function and symbol

Note: It is a common misconception that the shift piston must be in the center position for the two-pressure valve to connect through. This is exactly what would be an undefined switching position!

Example of use: Two-hand control with either a `two pressure valve` or as a series with two-way valves.

Pneumatics logic AND circuit

### Logic OR-valve or Shuttle valve

At the output 2 of this valve, the operating pressure is switched through as one of the inputs 1 or 2 are applied to the operating pressure.

Pneumatics - Shuttle valve - function and symbol

The logic OR-valve applies to a double check valve, which forwards the higher pressure at the entrance to the exit. If both inputs are pressurized, so the signal which arrives first is switched through to the outlet.

### Logic NOT with pneumatic elements

In this example, the funcion `NOT`is realized by means  of a pneumatic NO1 pushbuttom. The logic here is: if the button is not pressed, but way valve is actuated and the cylinder extended.

Pneumatics Logic Not

From the content:

0:00 Introduction Pneumatics

2:00 What is pressure?

3:09 Combined Gas Law, calculate a compressor

3:57 FRL Unit (Filter, Regulator, Lubricator)

6:49 Pneumatic circuit with indirect-operated DCV

7:33 Two-Pressure valve (Logic And valve)

8:18 Shuttle valve (Logic Or valve)

8:57 Indirect controlled systems

10:32 Pneumatic history part 1 12:26 Structure of a pneumatic circuit

12:34 Pneumatic history part 2

14:55 What is electropneumatics

17:29 Preview