Shuttle valve

A shuttle valve is a pneumatic or hydraulic valve with two inputs ( control lines ) and an output.

Logical OR (OR)

The shuttle valve is the technical implementation of an OR operation in the field of pneumatics and hydraulics: When applied to a pressure signal to at least one of the two inputs, an output signal is generated.

Truth table shuttle valve:

Design and operation

The shuttle valve is generally of a housing (in the graphic hatched), two input ports (side), an output terminal ( above, with outgoing arrow) ( spherical here ) and a switch body (gray).

Basically, the shuttle valve has only two defined positions. In each, an entrance is always locked from the switch body. The respective other input is thereby released simultaneously, so that from there a pending pressure signal can reach the exit. If both inputs are pressurized, so there are two options:

• If both pressure signals at different time points a, the signal arriving first routed to the outlet.
• If in contrast the two input signals of different pressure on, then the switch body shifts due to the pressure difference: The input to which is applied the lower pressure is thus locked ( in the graph will light blue) and the signal with the higher pressure applied to the output (dark blue).

Purpose

The shuttle valve is used in all pneumatic and hydraulic circuits, in which a logical OR operation of pressure signals of importance. It is used eg for the connection of two safety valves in a container to be protected. With this arrangement, a safety valve to the vessel is always connected and there is the opportunity to increase safety valves for inspection or repair without having to empty the container connected. Thus it can be switched in the event of a leaking safety valve on the other valve. Such an arrangement is required for larger pressure vessel for the storage of liquefied petroleum gas or other liquefied gases for pressure vessels and refrigeration systems.

In the hydraulic shuttle valves are used in load-sensing circuits and inlet pressure scales.

The shuttle valve also serves to implement a purely pneumatic self-holding circuit.