Two-pressure valve
A two-pressure valve is a pneumatic or hydraulic valve with two inputs (control connections) and one output.
Logical AND
The two-pressure valve represents the technical implementation of an AND link in the field of pneumatics. or hydraulics: If a pressure signal is applied to both inputs , an output signal is generated. However, if a pressure signal is only applied to one of the two inputs, no output signal is generated.
Truth table two-pressure valve:
| Entrance 1 | Entrance 2 | output |
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
Structure and functionality
The two-pressure valve usually consists of a housing (hatched in the graphic), two inlet connections (on the side, with incoming arrows), an outlet connection (above, with outgoing arrow) and a dumbbell-shaped switching piston (yellow) which is attached to the sealing surfaces with a plastic seal ( red) is occupied.
Basically, the two-pressure valve has only two defined switching positions. In each of them, one input is always blocked by the switching piston. The other input is released at the same time, so that an existing pressure signal can reach the output from there. There are two options:
- If the two pressure signals arrive at different times, the last signal to arrive is sent to the output.
- If, on the other hand, both input signals have different pressures, the switching piston shifts due to the pressure difference: The input at which the higher pressure is applied is thus blocked (dark blue in the graphic) and the signal with the lower pressure reaches the output (light blue).
Example: If there is now a pressure signal at only one input, point 2 applies: This input is blocked by the switching piston and the other input is released at the same time. But since there is no pressure on it, no pressure signal reaches the output.
Note: It is a widespread misconception that the switching piston in the two-pressure valve must be in a central position for correct functioning. It is precisely this that is an undefined switch position and therefore impermissible! It is also by no means necessary for the valve to function correctly at both inputs: This would be very difficult to achieve for technical reasons alone.
Intended use
The two-pressure valve is used in all pneumatic and hydraulic circuits in which a logical AND operation of pressure signals is important. Typical is z. B. the use in a so-called. Two- hand control , in which to operate a pneumatic or hydraulic system, two separate switches must be operated simultaneously to prevent the operator from reaching into the machine during operation. However, this type of safety circuit is generally not yet sufficient, since it can be manipulated very easily by the operator .
literature
- J. Dillinger et al .: Fachkunde Metall , 55th, revised edition, Verlag Europa-Lehrmittel. Haan-Gruiten, 2007. ISBN 978-3-8085-1155-8
- K.Stoll: Pneumatic controls , 11th edition, Vogel Buchverlag. Würzburg 1999. ISBN 3-8023-1805-6