Figure 6-25, diagrams A and B respectively, shows a road-patrol truck’s hydraulic system and a hydraulic circuit’s schematic, as a comparison. The truck needs three double-acting cylinders to operate its blades and dump body: a plow hoist cylinder for the front plow, an underblade cylinder, and a dump-body hoist cylinder. The truck also has a power-steering system operated from one-half of the double pump. (The steering system has been omitted from diagram B). The schematic shows that the three cylinders are operated through a three-spool, mobile directional valve fed from the large volume end of the double pump.