Directional control valves are the most widely used . . . and
the least understood . . . valves in fluid power circuits. Many
people are confused by the schematic symbol representations, and
have difficulty understanding the terms ways, positions, and
operators. Learning to read schematic drawings is similar to
learning a foreign language. To the trained eye, a symbol speaks
volumes even when no words are present. This chapter attempts to
take away some of the confusion and apparent magic of fluid
power schematic drawings, and thus help make designing and
maintaining fluid power systems easier. Directional control
valves can only perform three functions: - stop or block fluid
flow - allow fluid flow, and - change direction of fluid flow.
At first glance, the valve type shown in Figure 10-1 does not
appear to be a directional control valve. However, check valves
do allow flow in one direction and block flow the opposite
direction. Use a check valve in any line where back flow cannot
be tolerated. Also pilot-op