A two-way valve is generally used to control the direction of fluid flow in a hydraulic circuit and is a sliding-spool type. Figure 5-21 shows a two-way, sliding spool, directional-control valve. As the spool moves back and forth, it either allows or prevents fluid flow through the valve. In either shifted position in a two-way valve, a pressure port is open to one cylinder port, but the opposite cylinder port is not open to a tank. A tank port on this valve is used primarily for draining.