Shuttle valve and twin pressure valves are used for logic control. Shuttle valves are associated with OR logic and twin pressure valve with AND logic.
— A shuttle valve consists of a valve body and a synthetic ball or a cuboid valving element moving inside the bore in the valve housing.
— There are three opening. and A. If the air is fed to port. Port is closed and air moves to ‘A’.
— If air is fed simultaneously to port and P2 then air moves to A either from or or from both.
Fig. (a) Shuttle valve (b) Symbol of shuttle valve.
Twin Pressure Valve: In Fig. (a), a schematic sketch of a twin pressure valve is shown. This valve is also called an AND GATE. Here an output is produced if both the input signals are fed. This has three, ports — two signal receiving ports ‘A’ and ‘B’ (input) and an outlet port ‘Y’. When signal is fed to ‘A’ first, the valve spool moves towards ‘B’, closing the air passage from ‘A’ to ‘Y’ and hence the air from ‘B’ moves to ‘Y’. The reverse takes place if air is fed first to ‘B’. Then air moves from ‘A’ to ‘Y’. If air is fed simultaneously to both ‘A’ and ‘B’, then the spool remains in its already acquired position and air may pass to ‘Y’ from both ‘A’ and ‘B’ or from any of these two depending on the air pressure and spool position. Application of this AND GATE is shown in Fig. (b)