Shuttle valve
A shuttle valve is a pneumatic or hydraulic valve with two inputs (control connections) and one output.
Logical Or (OR)
The shuttle valve represents the technical implementation of a non-exclusive OR link in the field of pneumatics and hydraulics: If a pressure signal is applied to at least one of the two inputs , an output signal is generated.
Truth table shuttle valve:
| Entrance 1 | Entrance 2 | output |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
Structure and functionality
The shuttle valve usually consists of a housing (hatched in the graphic), two input connections (on the side), an output connection (above, with an arrow pointing outwards) and a (here spherical) switch body (gray).
Basically, the shuttle valve only has two defined switching positions. In each of these, one input is always blocked by the switch body. The other input is released at the same time, so that an existing pressure signal can reach the output from there. If both inputs are pressurized, there are two options:
- If both pressure signals arrive at different times, the first signal to arrive is sent to the output.
- If, on the other hand, both input signals have different pressures, the switching body moves due to the pressure difference: The input at which the lower pressure is applied is thus blocked (light blue in the graphic) and the signal with the higher pressure is sent to the output (dark blue) .
In both cases there is a pressure signal at the output. If both inputs are depressurized, the output also remains depressurized. This creates the desired OR link.
If the inlets were only connected to the outlet via a T-piece and if only one of them were pressurized and the other without pressure, the medium could flow away uncontrolled through the depressurized inlet and the outlet would remain depressurized. A shuttle valve is therefore indispensable for OR operations.
Intended use
The shuttle valve is used in all pneumatic and hydraulic circuits in which a logical OR operation of pressure signals is important. It is used, among other things, to connect two safety valves to a container to be protected. With this arrangement, a safety valve is always connected to the container and it is possible to dismantle safety valves for testing or repair without having to empty the connected container. This means that in the event of a leaky safety valve, you can switch to the other valve. Such an arrangement is prescribed for larger pressure vessels for storing liquid gas or other liquefied gases and for pressure vessels in refrigeration systems .
In hydraulics, shuttle valves are used in load-sensing circuits and in inlet pressure compensators .
The shuttle valve is also used to implement a purely pneumatic self-holding circuit .
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