Page 78 - Instrumentation and Measurement
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FIGURE 5.17 Operations required for an automatic machine operation.
5.3.2 Shuttle Valve
The most common form of directional control valve is the shuttle or spool valve. Shuttle valves have
a spool moving horizontally within the valve body. Raised areas, termed lands, block or open ports
to give the required valve operation. Figure 5.18 illustrates these features with a 3/2 valve. In the first
position, the shuttle is located so that its lands block off the 3 port and leave open, and connected,
the 1 and 2 ports. In the second position, the shuttle is located so that it blocks of the 1 port and leaves
open, and connected, the 2 and 3 ports. The shuttle can be made to move between these two positions
by manual, mechanical, electrical or pressure signals applied to the two ends of the shuttle.
Figure 5.19 shows an example of a 4/3 shuttle valve. It has the rest position with all ports closed.
When the shuttle is moved from left to right, the pressure is applied to output port 2 and port 4 is
connected to the exhaust port. When the shuttle moves from right to left, pressure is applied to output
port 4 and port 2 is connected to the exhaust port.
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